August 16th: Arduino Tips...

A few quick tips that I wish I'd learned sooner.

1) You can attach a button / switch to an arduino without an external resistor. You connect one side of the button to ground, the other to the digital input. Set the pinMode to input, then turn on the internal pullup resistor using the digitalWrite function. I like using defines for my pin numbers at the top of my file.


  #define SWITCH1         5

  pinMode(SWITCH1, INPUT);
  digitalWrite(SWITCH1, HIGH); //turn on pullup

Later, when you need to read the switch, just use digitalRead and test for LOW.

 if (digitalRead(SWITCH1==LOW))

    {

      //do something

    }

This method simplifies your circuit AND keeps you from running power to all your switches reducing the possibility of shorting your power supply.

 

2) You can use the analog input pins A0-A5 as digital inputs! Just number them 14-19 and use them for standard digital I/O.

Using the above code, you would simply define SWITCH1 as 14 and connect the switch to pin A0 on the arduino...

  #define SWITCH1         14 //A0

  pinMode(SWITCH1, INPUT);

  digitalWrite(SWITCH1, HIGH); //turn on pullup

 

Little tips go a long way to maximizing productivity and hardware capability...enjoy!

August 15th: Hockey Season!

My good friend Luis is a bit of a Hockey nut. He not only watches hockey (He's a Rangers fan...), he pre-plays the games for the Rangers on his xbox with his brother. He also has an "original 6" table hockey game with a custom cover made by his family.

I don't think that is the exact model, but you get the idea :)

A few years ago, I was scrapping an old air hockey table and Luis took  the scoring system and modified his table hockey game to use the scoring mechanism.

He cut out the goal area so the puck could go down into custom lexan fixtures that hold the air hockey table scoring switches.

These velcro to the bottom of the table hockey game. They are removable so the table can be transported and still lay flat.

Last year when I got into messing with arduinos, we were kicking around the idea of making a custom scoreboard for the table that would use the Adafruit WaveShield to play hockey arena sounds & music.

At the time I wrote out some basic plans, but focused on finishing my son's "control panel" and finishing my MBA.

A month or so ago, I found the NCR VFDs at Skycraft and this triggered the scoreboard idea again. I made a shopping list for Luis, he ordered the parts and off we went.

The project has come together quickly. We had an afternoon where we soldered up the WaveShield and modded his VFD for TTL serial. I have worked on the code a few hours here & there, and Luis has been working on getting the components mounted. Since I didn't have my shiny new welder this week (thanks UPS - once again you screw with my happiness!) I decided to really get moving on this project. I wrote most of the code logic yesterday and today we got the prototype case finished up. 

Here is the VFD mounted in the case. We had a little mix-up on the VFD dimensions, so the prototype has a little extra view of the VFD :)

Side view showing the lighted power button and power jack

A shot of the inside wiring - Arduino and WaveShield on the bottom right, VFD is the big board, buttons up top. We've since added an RJ45 "magic jack" with a SparkFun breakout board at the bottom. It will be the connection to the table switches and LEDs. The green wire coming up the middle of the VFD board is the TTL mod. 

  

.  So, how will this thing look in action?? Here it is next to the table. The wires on the side of the table are where the scoring / intermission LEDs will be placed.

And more action shots...

Intro screen...music will be playing...

Select the home team. The middle button is "next" and the right button is "ok" in this mode.

We are making the periods 20 mins like "real" hockey, but then making the clock run down faster. Not sure it will stay this way, but makes life much easier for testing because I can set the scale at a crazy high number and get periods that are a few seconds long :)

In game shot... (scoring switches not connected yet...) During the game, the right button is "play / pause". After a goal, the timer automatically pauses and then a button is hit to resume gameplay (after a short timer to allow the person hitting the button to "ready" themselves...)

I'm really excited to get the sound / music code integrated and get this thing connected to the table. I might even have to learn how to play!

August 8th: Let's WELD!

I've backed off the electronics design & testing for the last two weeks. I was in deep and needed a break. I've switched gears to disassembly on the Firebird. I've gone MUCH farther than I intended (as usual) and will likely keep going.

One of the next major projects on the Firebird is rectifying the swiss cheese firewall. The no-longer needed hole for the factory AC is a mess. It had been hacked in the past and the cover plate was gooped on. It wasn't panel bonded or epoxied, it was soft, pliable black goop. Yuck.

I want to do it right, so I've ordered a filler panel from Detroit Speed (this is a common modification since aftermarket AC doesn't go through the firewall) and now I'm learning to weld. Sure, I could use 3M panel bond, but what fun is that?!

Here are two pics of the major firewall hole...

I also have some transmission tunnel cleanup work to do. I've started it with the cheap Harbor Freight flux core box, but I'll wait for the real MIG box to show up before finishing it.

This is the "cover" the previous owner made to patch up the transmission tunnel.

He not only hacked the tunnel, he left a ridiculous amount of holes...

Here is the "after" shot from me filling (and grinding, and filling and grinding...) the holes...

And the new "cover" made from 16 gauge steel...

As usual, I'm trying to get the boys engaged in the process. I don't think they understand yet just how cool welding is. My little guy went shopping for supplies last night AND he watched the GMAW (MIG) WIRE FEED video I purchased.

Here he is, ready for action!

When I took him to the Lincoln Electric site to show him the welder I ordered, he saw that they make an Iron Man welding helmet. I didn't have much choice on the design of my new helmet after that. I suspect I'll have to fight him for it :)

For those of you that are into such things - I've ordered a Lincoln Weld Pak 180, which is a 220v MIG welder. I also ordered the spool gun for welding aluminum and a cart. I will be purchasing an Argon / CO2 mix cylinder for welding steel and a pure Argon cylinder for welding aluminum. Yes, I know TIG is the fancy way to weld aluminum, but this was an easier (and cheaper) way to get started. I need to prioritize my ability to easily weld old steel bodywork and MIG is the way to go for bodywork. If I get decent at this, I'll try TIG in the future.

I also think it will be MUCH easier to teach the boys MIG.

Wish me luck!

July 24th: General Update

Last weekend I received the BTS550 and BTS555 High Side Switches from Infineon. As usual, my comprehension of the datasheet prior to ordering didn't really prepare me for what I ordered. I missed that these are NOT microcontroller friendly devices. When they are OFF, the voltage at the microcontroller input is the car  power voltage, so thats 12+ volts. Good thing I was using the Rugged Circuits Gator+ and not a standard Arduino, or I would have taken out some pins. The BTS could handle more current, but still not enough to drive the big fans with just one device and a smallish heatsink.

That evening of tinkering was a pretty big setback and I ended up pretty discouraged. If only they made the IPS6011 with a higher current capability. Sigh. I took the rest of the weekend off from electronics and continued the garage cleaning. It was VERY productive and I'm almost done.

During the week, I decided to let the project sit in the background, maybe my motivation would return or I'd have some epiphany.

A few things did come to mind:
1) I should be able to gang the IPS6011 for higher current capability. I emailed International Rectifier to see if they had any design considerations for ganging them.

UPDATE - response from IR (on SUNDAY MORNING!!)


Because IPS parts have HEXFET outputs, it may appear possible to parallel them., because as you know the Rds(on) of MOSFETS has a positive temperature coefficient which aides current sharing in parallel part situations. However, with IPS parts there is a practical difficulty as a result of the built-in over current and thermal overload protections. These protections are not built-in to discrete MOSFETS. There will be small differences in the actual Rds(on), the over-current and thermal trip points due to normal parametric spreads in these characteristics between a number of IPS parts. Which means that in an overload situation one part will be inclined to shutdown before the others. With IPS parts the over current protection is reset when the input signal is cycled from on to off to on and over-temperature is automatically reset when the junction temperature cools by around 7*C. With one of the parallel parts shutdown, the total load current will be shared with fewer devices which in turn will carry an increase in current and tend to shutdown in a chain reaction. As the input signal is cycled, every part will try and turn on again. If the input cycling is automatically repetitive with the current overload condition still present, the junction temperatures will tend to rise progressively until the first device shuts down due to over-temperature. Eventually all devices will shut down initially due to over current and ultimately due to over-temperature. The time for all parts to shutdown will be a function of the magnitude of the over-current, the individual device characteristics and the thermal conditions of the application with respect to heat sink ratings and device local ambient temperatures.

We do have many customers using it in parallel.In a parallel configuration of devcies, the major consideration is effective current sharing.Also, as these devices operate with current sense feedback, extensive circuit testing would 
be needed to ensure proper operation. We do not have reference designs / data for such an
application. However, a point to note is that during circuit turn-on, for a slowly ramping 
current (such as for an inductive load), the paralleling works better. For fast ramping loads
paralleling may be more difficult. You would also have to ensure proper feedback for each of 
the devices in parallel.

2) I've been testing with my WORST-CASE load - a GIANT cooling fan. I can always relay these big inductive loads and go on with life. I need to move forward with my plan to measure each load in the car to figure out if a single IPS6011 circuit for each will suffice. With a small heat sink, I proved them for an 18 amp inductive load. With a larger heat sink and a non-inductive load, I may be able to push higher.

3) Big mosfets aren't usually shoved in little cases - in fact, the cases themselves are typically the heatsink - car audio amplifiers and car ECM / ABS modules come to mind - the cases for most car modules are thick aluminum and many have fins molded onto the case. I may hit a "u-pull it" junkyard for some case options...

Last night I finished pulling  the factory harness. I found even more crimp connectors, taped connections and wires to nowhere. The seats are out, the carpet is almost out. I need to pull a few more things, then get started putting Humpty Dumpty back together again. Once again I'm having that "why did I go this far" feeling. I sure like doing this to myself... I need to either get this wiring harness project moving or just order one to move on - but that sure wouldn't be as much fun...or frustration :)

Vacuum Florescent Display

I picked up one of these displays yesterday at SkyCraft. Someone was nice enough to create a documentation page for them, and has a youtube video example...

Vacuum Florescent Display - TechNet

Update:

After reading the documentation above, I got out a DB9 serial cable and wrote some quick Processing code to test out the VFD. It worked according to spec and I had it cycle through the character sets (including an undocumented third set). Reading deeper into the docs above, I saw the comment about RS-232 to TTL conversion by an onboard IC. Feeling newly empowered by knowledge and tools, I got out the logic analyzer and found the pins that had the TTL serial feeding the display microcontroller. Once I confirmed the pin, I looked for an open test pad to solder to - no such luck. I downloaded the datasheet for the microcontroller, found the rx pin, attached the analyzer and confirmed it had the TTL serial signal. This time, there was an open test pad, I confirmed it had TTL serial, and then soldered a jumper wire from the test pad over to one of the unused pins on the main connector. I got out an Arduino, quickly ported my code from Processing to Arduino and had the same character set scroller running from the Arduino.

So what's ironic is that today I set out to connect this display to an Arduino by building a MAX232 circuit that would convert the Arduino TTL serial to RS-232. I had ordered the wrong capacitors and couldn't build the circuit - but then later in the day, determined the reverse conversion was happening on the VFD and I could just cut out the middle man. I'm no longer upset about ordering the wrong caps - this was a WAY better learning adventure with a better outcome. Learning is fun :)

July 11th: Homemade Solid State Relays...

This week while searching for enclosures for this microcontroller car wiring project (that still needs a name), I had the idea to mount the IPS6011 High Side Intelligent Power Switches inside ISO Micro Relay cases. The micro relays have 5 connections and Delphi makes some great modular enclosures to hold them. Once I arrived home from the beach and the IPS6011s had arrived, I purchased a few micro relays to see if they would fit. Short version - they fit with minimal effort, and can convert an existing micro (coil) relay into an IPS (solid state) relay in about 20 minutes with some practice. You can see the ugly results below. I'm sure there is a better way, but this is the result of my first attempt. So far I've switched and PWM'd a 10 amp inductive load (automotive cooling fan) without any issue - with the top reinstalled. PWM switching of a 10 amp load makes these things HOT. I've had it over 200 degrees Fahrenheit which is still 100 degress below the thermal protection threshold. For now, the only heat sink is the existing coil mounting tab which is also the main power terminal.

Here are some assembly pics...

Some other notes: The diagnostic output works great. I'm using the simple version of the diagnostic circuit which requires no components other than the resistor that is in the relay case (and the internal pull-up resistor in the Arduino circuit).

So far I've run everything off the 12amp bench power supply. The next tests will be off a car battery - I need to test some larger loads, and see if I can hit thermal shutdown. Destructive testing is fun - I'll have the fire extinguisher handy :)

UPDATE:

Full size car battery tests - I can run one cooling fan long term (a 10 amp load) and the temperature stays stable at about 125 degrees. Running both fans (in-rush current over 20 amps, then settles to about 15 amps) causes the temperature to skyrocket (even without PWM) and it hits thermal shutdown (I thought there would be a longer off cycle, it seems to go off, then right back on, generating even more heat - I didn't let it keep going...) and the diagnostic pin DOES pickup the issue. I'm wondering if more heat sink would make the difference...I'm tempted to build my aluminum block relay...

No, I haven't figured out why both fans don't seem to draw 2x the current...something is odd...

In my next Digikey order, I think I'll try some other higher-rated power switches. What is nice about my "modular" concept is that I could use inexpensive switches for smaller loads and more expensive switches for larger loads as needed. The IPS6011 were $4.90 each - and these things go up to almost $11 each. When you plan on 30 of them in a system, that cost adds up fast. I think my next part to try is the Infineon BTS50085-1TMB-ND  - $6.95 each, but rated for 44 amps. It is a 7 pin part, but use 4 pins for the output - which makes a lot of sense. They drop the microcontroller ground, which is interesting - but if it works, its one less connection :)

I'm also tempted to try the Infineon BTS555E3146IN-ND - it is $10.15, but rated for 165 amps. I don't know how that's even possible, but if it could PWM my BIG cooling fans (35amps each...) I'd be very willing to spend the $20 for two of them.

Update - July 12th - those BTS50085's are on backorder - DOH! I'll be getting a few of the BTS555s to play with in the mean time. I also made a billet relay case tonight. I've always wanted to make something out of billet, it was very, very time consuming, but came out...pretty nice. I should have taken some pics but I quickly mounted it to my PCB-mounted IPS6011 as a heatsink to see if it would add amperage capacity at a reasonable heat. Turns out, that in a room with some moving air, it stabilized about 180 degrees with both cooling fans as the load. When I stopped all moving air in the room, it climbed slowly to about 200 and stayed there. I think that is still too hot, but I was encouraged to see that a little bit of aluminum went a long way - before I would run them for about 10 minutes before it would go into thermal shutdown. Tonight I went over 30 minutes before I shut it down to get some sleep. More experimentation to come...

July 10th: More Power!!

I've been annoyed by not having a benchtop power supply for sometime. When I'm working with basic Arduino stuff it isn't a big deal because I get 5v off the Arduino - but when I'm working with 12v control, I'm constantly finding some other wallwart or other source, hacking something together and typically without any regard for safety - for me or the circuit. I've been looking at benchtop supplies online and had picked out a nice Extech, but just couldn't justify the cost. I decided to stop by Skycraft yesterday to see if they had something. I had the choice between a new 30 volt / 3 amp digital meter power supply from some unknown Chinese manufacturer for $130, or a used Extech 382222 15 volt / 12 amp analog meter power supply for $95.

I chose the used, known good manufacturer, analog gauge power supply with MORE POWER!

Right now the Extech is pumping out just over 10 amps to an automotive radiator fan at 13.8v. It is very stable, and handles overcurrent gracefully... 

In my haste to leave the store (due to my 7-year old being mad that I wouldn't buy him this large plastic wheel from whatever), I forgot to buy some banana plug leads...but I found some banana plug adapters in the home stereo connector drawer, so I'm good for now.

I'll likely build a plug in 5v supply so that I can easily have dual voltage - but no big hurry, as I mentioned, my Arduinos all have voltage regulation on them...

Hey, Lego my Droid, you remote-controlled fiend! (video) -- Engadget

Hey, Lego my Droid, you remote-controlled fiend! (video) -- Engadget

I've been saying for some time that the next generation of hobbyist devices are all the Android smartphones that fall out of use - in a small package you get a CPU, Battery, Display, GPS, Wifi, etc. I'm waiting for someone to release an Android version specifically designed for embedding - a "headless" version more or less. These videos show that we are headed that way...

July 9th: Time to think...about Modular Electrical Centers

Vacation has its benefits - one of which is the ability to clear the mind & think about a topic over a few days. When we are at the beach, I usually have a few hours every morning where others are still asleep, so I go for a walk on the beach. Since Candy is back in Orlando, I haven't been taking the morning walks, but instead sitting on the balcony watching the sun come up while surfing the web. I had some targeted web surfing this week - mostly figuring out how to get this Firebird project moving so I can have the car moving in September as it starts to cool down.

Earlier in the week, my web surfing paid off when I found the MOSFET I needed. This is the most critical part in the whole system - the high-power switching. Once I knew that the IPS6011 would meet my needs, I started thinking about enclosures - specifically the underhood enclosure. I'm not worried about the enclosure for the dash or trunk, since those don't need to be weatherproof to meet my needs. The underhood enclosure has to withstand a good deal of heat, moisture, etc. and ideally, LOOK GOOD. :)

I spent lots of time searching for IP67 rated enclosures and sealed connectors or cable glands. I found a few options, but nothing was really making me happy. I knew that Delphi weatherpak and metri-pak connectors were the way to go for automotive stuff, so I headed to the Delphi site. Once there, I found the catalog I'd seen once before, but had forgotten and I had an AWESOME thought. Modular fuse blocks!

I had to turn my thinking inside out - instead of an enclosure that was sealed and contained the microcontroller (or I2C expander), the 10 IPS MOSFETs and the 10 fuses, why not do the fuses externally. I'd also had this crazy thought for some time - What if I could fit the MOSFET in a fuse housing, then I could just plug them into a fuse block. Unfortunately a fuse only has 2 connections and the IPS MOSFETs need 5. Then it hit me - a Relay has 5 connections. I can make each IPS into a module that is the same size as a relay and they can just PLUG IN. Woah.

My first thought was to buy relays, gut them, install the IPS and any indicator LEDs and reseal them. Seems like a lot of work AND it then looks like a relay when it isn't one. I was also worried about the thermal load of the IPS in that little case. If only I could make the case from aluminum and it would act like one big heat sink. THAT'S IT! I can buy aluminum block, cut to size, drill out for the LED(s) and the IPS and attach the IPS right to the aluminum case. I can use epoxy to "Pot" the IPS and terminals in place. I'm guessing this puts the parts cost of each module at ~$10. For the prototypes, I'll machine them at home, but if it works right, I can see ordering them nicely machined, looking all fancy and mac-book like :) 

Ok, so now I solved for the IPS and for the fuses, but I still need to house the microcontroller or the I2C expander (just called the "control circuit" to make it simpler). Both can fit in very small packages (if ordered with SMT). 

Assuming the use of the 4 module electrical center above, I would have one with mini fuses (bottom left in the pic above), and 2 that hold 6 micro iso relays (not shown). That gives the capacity for 12 fused IPS circuits, and a spot for two extra relays if needed (cooling fans, etc). That leaves space for one more module, which can contain the control circuit. 

I started counting connections...

Connections to "master" = 5

+5v 

Gnd

I2C SCL

I2C SDA

Interrupt request (saves the master polling for diagnostic issues or inputs)

Connections to IPS circuits = 24

1 control line per circuit (lets stick with 12 circuits for now) = 12

1 diagnostic line per circuit = 12 

So for a 12 circuit system, I have 29 connections.

I started looking for connectors, trying to think of how I'd mount the module and the connectors. I kept thinking, "there must be an easy way" - then I realized - the modules that hold 6 relays have 30 connections...hmmm...

Sure enough, I can take the same approach as the IPS. Aluminum enclosure (or plastic since I'm not worried about heat), spades stick out the bottom for all the connections, potted. The entire thing just pushes into the module. I'm a little concerned about removing it with 30 connections, and about getting all those spades mounted right - so I'm not sold on this one yet. There may still be a better way, but I need to get the electrical center here to see it.

What I LOVE about this option, is that it is crazy modular. You can scale the number of circuits up or down very easily. Only need 8 circuits, you only have to make / buy 8 of the IPS modules. Fry an IPS (not sure how given all its internal protection), just pop one out and replace it. If they can dissipate heat properly, I might be able to even put two IPS in one case DOUBLING the current capability (BIG cooling fans with PWM...) Best part is minimal manufacturing, and it should blend into the engine compartment since people are used to seeing these electrical centers and not really giving them a second look. With this design, there are quite a few electrical centers that could be used - just a matter of picking the one that meets your needs.

mouser.com carries all the delphi parts and they can all be ordered by the piece. I priced out the modular center concept above and BEFORE terminals, it is ~$50. I'm guessing I'd spend another $20+ on terminals. While this might seem pricey, I will no longer need a large PCB design...A small and simple PCB for the control circuit is likely all that is needed.

I'm sure there is more to be solved - but at the moment, this feels like a VERY good direction. If it works out well, I can use the same mounting system in other parts of the car - but without the need for the sealing, I may keep it simpler. Then again, this may prove to be the way to go all around...that electrical center is only 7.24" x 4.6" x 1.65"...which would fit well in any of the spaces I'm thinking...

I haven't pulled the trigger on the order yet. All this is contingent on the IPS working the way I need. The IPS order should be at the house today - I'll get them tested, then I'll build one of my micro-relay aluminum IPS modules, make sure it can take the heat - if that all works, I'll order the electrical center and get started on the control circuit mounting. I suppose I should get to work on the actual control circuit, but for some reason that seems "easy" to me once the IPS and weatherproof mounting get solved. I'm sure I will regret thinking that later :)

July 8th: Lego Machine Gun

We brought the Lego NXT 1.0 Robot set to the beach with us. After a minor setback (Dad left the CD in the box at home, but when Mom went back, she was able to zip it & send to Dad...), we were operational.

The boys decided they wanted to make the machine gun from nxtprograms.com. We started it last night, then about step 17 decided it was getting late. We finished it today and immediately test fired it. It shoots all 10 "bullets" (three hole technics pieces) in about 2 seconds (as seen in the video below). The boys think it is "AWESOME!"...

July 6th: Arduino 3x3x3 LED Cube

I'm keeping the boys entertained at the beach this week. My need for constant stimulation has CLEARLY been passed onto them, so yesterday was an action-packed day. We started the day by building a 3x3x3 LED cube driven by an Arduino. 

I've seen these on youtube, the Arduino forums, Make, Instructables, etc. and have wanted to make one for a while. I reviewed lots of the different instructions and settled on this one from Instructables since it included Arduino animation code.

Before we left for the beach, I made a quick wooden jig on a 2x4 scrap. I created the dot grid using the "Square Dots Graph Paper PDF Generator". I made a 4x4 grid, even though I only intended to build a 3x3 cube. If it worked out, I figured 4x4 was the next logical step and I'd already have the jig :)

After the boys crashed on Monday night, I made the first two layers and setup the Arduino and breadboard so that we could build one layer together, attach it and they could see results almost immediately. For those keeping score, yes, I did bring an Arduino, LEDs, a soldering iron, solder, eye protection, pliers, snips, a breadboard, jumper wires, and alligator clips to the BEACH. It rains a lot here, OK?! :)

The completed 3x3x3 Red LED Cube...the cathodes are all connected together on each horizontal layer and the anodes form the vertical risers. Lighting a specific LED means activating ONLY that cathode layer and that anode riser. The microcontroller does this very quickly and takes advantage of persistence of vision to make it appear that multiple lights are on at one time.

The pics and video don't express the "cool" factor of the 3 dimensional light animation. If I had the patience, I'd build a really large one of these - say an 8x8x8 or maybe even an RGB one - but I don't have the patience to spend a week bending and soldering. I'm surprised I haven't found links yet to buy them presoldered out of China :)

Why would you want an 8x8x8 RGB LED Cube? This video shows how cool they are...

And just in case you were wondering, after building the LED Cube, we went bowling, had lunch, went to Best Buy to get new video games, played the new games for a bit, went snorkeling, threw the Nerf  whistling football on the beach, went grocery shopping, made dinner, played more video games, played tennis, went swimming, played two games of  chess with the large set on the sun deck, played more video games (while Dad did laundry and dishes) and all passed out at 10pm :)  Whew!

July 5th: Seek and Ye Shall Find!

After my first rushed attempt to get MOSFETs for the Firebird microcontroller project that still needs a name (Maybe I should have a naming contest!), I'm taking my time researching to determine the right part. I've been keeping a list of candidate MOSFETs here.

Yesterday, while sitting somewhere, "relaxing", I went on a marathon component web search. I just kept thinking that I couldn't have been the only person trying to solve this problem. I made a list of my "ideal output stage" features:

• 25 Amp continuous High-Side Switch
• ATX or Mini-ATX fusing
• Fuse Blown detection
• Open circuit detection
• Short circuit detection
• Current measurement
• Transistor Heat detection
• Logic-level control (safe for microcontrollers)
• PWM capability for "soft-start" of load
• Manual override switch in case of microcontroller failure (limp-home mode...)

Given this list, I went searching for circuit designs and components, expecting that I'd use one of the MOSFETs I'd already found plus some extra components to keep the MOSFETs safe.

One of the best ways to find microcontroller-safe circuits is to search with Ardunio or PIC in the search terms. Sure enough I tripped on this post - "MOSFET to drive load, cables". I saw a reference to something called an Intelligent Power Switch. Now THAT sounded like what I was looking for...

Sure enough, I hit the jackpot... Meet the IPS6011...Datasheet

Features
• Over temperature shutdown (with auto-restart)
• Short circuit protection (current limit)
• Reverse battery protection (turns On the MOSFET)
• Full diagnostic capability (short circuit to battery)
• Active clamp
• Open load detection in On and Off state
• Ground loss protection
• Logic ground isolated from power ground
• ESD protection

Description
The IPS6011(S)(R)Pb Switch (IPS) for use in a high side configuration. It features short circuit, over-temperature, ESD protection, inductive load capability and diagnostic feedback. The output current is limited to the Ilim value. The current limitation is activated until the thermal protection acts. The overtemperature protection turns off the device if the junction temperature exceeds the shutdown value. It will automatically restart after the junction has cooled 7°C below the Tshutdown value. The reverse battery protection turns On the MOSFET. A diagnostic pin provides different voltage levels for each fault condition.
The double level shifter circuitry will allow large offsets between the logic and load ground.

Digikey sells the IPS6011 for $5.57 each. While this seems expensive at first, if I priced adding all the other components for thermal protection, logic-level MOSFET driver, etc - this is very reasonable, AND a big space savings. I don't get current measurement (I don't know why I really needed it...) and it is limited to 18A continuous (but has current limiting above 60A, so good headroom for in-rush current), but it looks like the right component!

I then found the application notes for the IPS60xx series - This thing is DESIGNED for my application - switching automotive loads! The application notes explain what happens if you disconnect the battery with the alternator running, if you remove the battery with active inductive loads, etc. I wanted to try to make the system resilient, this thing is perfect.  

Some concerns: 

1) 18A Continuous limit - I really don't think this is a problem since I plan to run most devices discretely - for example, headlights will be split into driving lights, lowbeam and highbeam vs. one circuit that powers all three. This will likely put a fully-loaded car near 30 circuits, which means $167 in just these components. I never said this would be cheap :)

2) PWM - The max switching frequency is listed as 0.3kHz which is 300Hz. The standard Arduino PWM is 500Hz, but a little research showed that the next step down is 250Hz, and there are even lower frequencies. I don't know enough about PWM to know if that would give me soft-start if needed, but it seems promising. 

I need to get a few ordered (Not ordering 50 of these!) and then learn how to use the diagnostic circuit works (you have to "switch-in" two different resistors to find some detailed problem states - not sure if I need to know those specifics, versus just "something not right...")

July 2nd: Logic Analyzer added to the toolkit!

This is a screenshot after playing with the Saleae Logic Analyzer for a few minutes. I attached probes to ground, I2C SCL, and I2C SDA on the microcontroller network and poof, I can inspect the traffic. Above you can see me sending one of the slave microcontrollers a 5 byte command with a 16 bit CRC attached.

I'll be learning how this thing works over the next few days and it should save me lots of debugging when I make silly mistakes. I also hope it will let me hack other devices much faster since I will be able to inspect their I2C, One Wire, or Serial communications :)

June 23rd - PegBreadBoard

I was showing a coworker the latest pics of the car wiring harness project and he used the word "breadboard" referring to my big pegboard project case. I realized I had made a PegBreadBoard! Sure enough, it lets me prototype without making permanent physical connections, just like an electronic breadboard. It has a spacing grid for mounting components, just like an electronic breadboard. I like it!

Here are some recent pics with some components mounted...

The switches are mounted in the top panel with wiring underneath, and the microcontrollers are mounted on the bottom panel, and their interconnect and power wiring (not yet installed in this pic) run underneath the bottom board. The microcontrollers are mounted on thin abs black plastic using industrial velcro, and then the abs panels are bolted to the pegboard grid. Very easily movable if my design changes. The big black cables are the USB connections for programming / logging.

The second abs mounting pad in the center section will be used for the power supply - or that is my current theory anyway.

I currently have power + I2C between the controllers and can run my prior code testing the I2C communications, so I'm back to where I was before - next step is to add code to detect all those switches, then DO something :)

The serial LCDs I ordered still haven't arrived, so I'm chasing them. I'd like to get them on the pegbreadboard for debugging output...

More soon...

June 22 - Getting Organized

My garage is ALWAYS a mess. My hobbies consume lots of space with the tools / parts / half-finished projects all trying to coexist based on my focus at that time.

I've given up trying to find the "big weekend" to clean it out, so I'm working on it an hour a night. Its not AS hot as 2pm on a weekend, so I'm making the best of it.

When I added the new garage, I set it up for car + electrical work. Later, when I thought I was buying a CNC router, I started moving all the car + electrical stuff to the old garage to make room for all the wood stuff in the new garage. I never bought the CNC router, but I also never completely rearranged the garage. I have this really cool shelving system that my father-in-law found in a Time / Life woodworking book. It is ROCK solid and can hold anything - and it runs floor to ceiling. I built the first set 5+ years ago, then last year (or was it two years ago?) I did another wall. I have my power saws / belt sander mounted to these wood shelves, and I slide them out to do work. I take the shelf and clamp it to saw horses - poof, instant wood shop. Here is a visual to help...

With the 2 walls I have 8 sections of these shelves (and have the routed 2x4s to make another few sections). This shelving system is very reasonable to build, very strong (you can stand / jump on a shelf) and will last forever (unlike those #*&% plastic hardware store shelves). If you want the instructions, let me know :)

This weekend I was trying to find a home for my drill press - it was one of my nice craftsman workbenches taking up space, and I didn't want it in that garage. It dawned on me that the shelves could actually be workspaces. So the drill press was moved onto a shelf (not mounted, because I could NEVER slide out that shelf anyway). I also mounted my bench grinder on the left middle shelf (the Ryobi) although I moved the other orange bench grinder and mounted my vise on the back of that same shelf. Now my workbenches are clean, I didn't have to drill holes in the workbenches to have my grinder & vise mounted, and everything fits in space I already had. I still need to find a home for some crap that was on those shelves, but the other shelves clearly aren't space optimized anyway...

Next, I decided I wanted to get my airtools off the main workbench pegboard. I don't use them that often and they were taking lots of space. I realized I had some empty space above my compressor, so I grabbed a piece of geartrack, cut it in half, and poof, my pegboard is clean (of airtools..._)

This also found a use for 4 of the 12 geartrack bins I purchased 3+ years ago, but never used. I also installed another piece of geartrack above the workbench pegboard (about 18" below the ceiling), put the last metal shelf up (yet another item that's been sitting here for years waiting for a use) and put some of my hobbyist kits up on it.

I will keep up this "hour a night" routine for a while to see how far I get, and maybe hit it hard this weekend.

I'm doing all this so that the garage is ready for an intense electronics + car work phase this summer / fall. When the garage is clean and tools / parts are organized, my productivity soars. Now I just need to find a place for a whiteboard out there so I can make a big project list...

June 19th: Phone Geek Day!


When I woke up this morning, I put on my tshirt with the little green Android on it. I guess I knew it was Phone Geek Day!

• Bought the 10 year old his first phone - a T-Mobile My Touch 3g Slide. Android 2.1 - He's VERY Happy.
• Upgraded the old 2G iphone to 3.x firmware, activated, unlocked & jailbroken. Gave it to the 7 year old for wifi use only. He has a "phone" too, but no calls / text. Basically an iPod touch, but it got me past the phone envy.
• Upgraded Candy's My Touch 3g to 2.1 (cyanogenmod) from 1.6. She gets to catch up on some of the Android features she's been missing.
• Upgraded my old G1 from cyanogen 4.x to cyanogen 5.x (Android 2.2) - it will be the garage phone for when my hands are greasy and I want to check email, search for something or control airtunes. Wifi only - no SIM.

June 16th - Expensive Lesson:

I received the MOSFETs from Hong Kong today. I bought 50 of them at $1 each + $5 shipping.

I'd ordered these because I saw them recommended on the arduino forum for switching high amp loads with a microcontroller. I did some research and pulled the trigger to get them here.

I pulled that forum post back up tonight and started thinking about building a perfboard to do some load testing. As I'm looking at the schematic, I realized my basic transistor knowledge missed a rather important item. I couldn't really explain the difference between NPN and PNP before - but now it is crystal clear. NPN allow you to switch GROUND, and PNP allows you to switch POWER. I want to switch power, and I have 50 NPN transistors. Oops...

Now I need to identify another transistor and get them ordered. I think I'll read the "Practical Electronics for Inventors" section on transistors a few more times before I spend more money :)


Update:
I'm using this post to summarize what I'm learning as I head to picking new MOSFETs

1) P-Channel MOSFET since I need to switch power, not ground
2) Low RDS reduces heat
3) I need 25A capability, but it is typically recommended to buy 2x capacity, so near 50A
4) Since I'm working with microcontroller voltage (0-5v) and switching 12-14v, I'll need to use drivers, since the difference in potential would be too high and the MOSFET would always be on. This means I don't need "Logic Level" MOSFETs since I will be using drivers.

Candidates:
1) STP80PF55 - P-channel 55V - 0.016Ω - 80A - TO-220 - $2.67 @ Digikey
2) IRF4905PBF - P-channel 55V - 0.02Ω - 74A - TO-220 - $2.81 @ Digikey
3) FQP47P06-ND - P-channel 60V - 0.026Ω - 47A - TO-220 - $2.26 @ Digikey (Used in the Arduino RC Lawnmower)


Other random notes:
1) You can MULTISELECT digikey filters. DUH. No wonder I've always struggled to find items. DUH.

June 14th - More parts ordered...

I read about the VDIP2 online, then by chance, my latest read "Practical Arduino" had a project which used the VDIP1 module. Since I'd like to have configuration separate from logging and the VDIP2 has 2 USB ports and was only a few dollars more, I thought "why not?!"

The same project was also automotive based and had a power supply design that used a different voltage regulator than I am accustomed to using. It is a "low drop out" model (LM2940CT-5.0) that can handle the low voltage conditions during cranking. The power supply design also deals with overvoltage and provides a capacitor that acts like a battery to allow shut-down time in the event of total loss of power. Very cool and highly PRACTICAL. I've ordered the voltage regulator and some other parts necessary to make the power supply (oops, just remembered that I forgot to order the cap...) for when I get to automotive use - that will be some time, but good to know there is a design ready. I included the I2C buffer chips and some sockets in the order. I'm thinking that they can't hurt, so why not have them on hand if needed.

June 9th: The Project Evolves & my learning continues...

I've started mounting mini switches in the pegboard lid of the project box. I think I'll teach Adam to solder and have him practice on all those switch leads soon :) The pegboard worked out really well since I didn't have to drill any holes, and I get a nice alignment grid...

I've been doing lots of thinking in my "in between time" this week - and "picking the brains" of some people I interact with. I'm using this post to document those thoughts and I'll share some parts I've ordered, as well as some tools / books that I think will increase my learning.

Thinking:
Most of my thinking has been about the "configuration" for a specific car. How will an input trigger lead to output commands on a specific slave? I don't want this logic co-mingled with all the send / receive code on the master, and I'd rather not mess with reflashing the gator+ each time I want to change the behavior of a specific output.

For now, I have an array structure in mind that I think will do the trick.

Example:
Pin 5 on the master is wired to the headlight switch.

In the master's main loop(), all inputs are read >50 times per second

A Pin 5 read returns LOW showing that the switch has been turned on (You can switch ground instead of 12v+ so you reduce the possibilities of short circuits under the dash and the size of the wires to switches, etc)

The array is read to locate all rows where the first integer is 5 (for pin 5)

In this case 3 rows are found:

Input Pin, Slave, Command, Var1, Var2, Var3, Var4 

[05][01][01][01][07][00][00]

[05][01][01][01][09][00][00]

[05][02][01][01][11][00][00]

So, this means that three commands should be sent (these are hypothetical...)

[05][01][01][01][07][00][00]

Input Pin: 5

Slave: 1

Command: 1 (this is the on/off command)

Var1: 1 (this means turn ON the output pin)

Var2: 7 (output pin 7 is the pin to be turned on, and output 7 on slave 1 are the headlights)

Var3: 0 - parameter not used for this command

Var4: 0 - parameter not used for this command

[05][01][01][01][09][00][00]

Input Pin: 5

Slave: 1

Command: 1 (this is the on/off command)

Var1: 1 (this means turn ON the output pin)

Var2: 7 (output pin 9 is the pin to be turned on, and output 9 on slave 1 is the dash lighting)

Var3: 0 - parameter not used for this command

Var4: 0 - parameter not used for this command

[05][02][01][01][11][00][00]

Input Pin: 5

Slave: 1

Command: 1 (this is the on/off command)

Var1: 1 (this means turn ON the output pin)

Var2: 7 (output pin 11 is the pin to be turned on, and output 11 on slave 2 are the taillights)

Var3: 0 - parameter not used for this command

Var4: 0 - parameter not used for this command

This would be a very simplistic "if input" "do something" without any real logic. My goal sometime soon would be to try to map out the full operation of a car in this structure to see if I need something more fancy. I have another more complex structure in my head that would maintain a state machine and then allow commands that modify the state machine, allow if / then logic, etc. but that might be overkill.

Once I know the size of this array, I can determine if searching it for a high pin number is CPU prohibitive. I may need to add an index to the array and then have a lookup table like

Input Pin, Start Index, End Index

This would allow me to quickly go to the commands for that input pin. However, if the total command list is only 50-100 items, the other array may not be worth the overhead.

This array structure could easily be read from EEPROM, SD Card, etc - which would allow changing of the car's configuration without reprogramming. For now I'll just build have the array setup in code, but it seems like a good way to go. I can't help but feel like I'm reinventing the wheel here with a command structure and array storage, so I need to look around to see what others have done before. For those with automotive knowledge, there are standards for this stuff - my I2C network & messaging is really a simplified CAN. I don't plan to interface this stuff with other hardware, so I figured CAN was overkill.

I've also been considering the power consumption of the 3 gator+ boards since they will be on all the time on a car that doesn't get much use. There is a sleep mode I'll investigate and I may need to switch the LCDs in some way to reduce their power consumption. It may also be possible to leave just the master on and power down the slaves until needed.

Parts:
LCDs - I know I want the master node to have a serial LCD for output of important items, I'm not sure about the slaves. The "control panel" used a bare LCD and took WAY too many I/O pins, so I spent a little more money and ordered serial / I2C 20x4 blue / white displays. I bought 3, even though I may not use them for slaves long term, they are really handy for debug output, so why not have them for now. I will try them in I2C mode, but I'm not sure I want any extra traffic on that bus, so they will likely get connected to the spare UART on the gator+ boards. This way, I have the option.

I2C Buffer ICs - I found these last weekend - the I2C network is working great now, but for future projects, I really like the idea of I2C instead of ethernet over long runs of cat5. I almost ordered them, and was already designing the perfboard in my head when I saw this line - "Breakout board available soon. This board will enable easy remote I2C bus extensions with standard cat-5 cable. With RJ-45 connector, breakouts for unused cable pairs, option for providing remote power and selectable bus pull-up resistors."  Perfect. I'll wait for those boards to be available, and if I suddenly have I2C problems on this project, then I'll grab the ICs at that point. This type of learning is so awesome, I just keep adding to the toolbox of components I know exist and I know how to use if needed.

Storage - I want some way to store the car-specific configuration and read that configuration at system startup. I'm looking at several options - SD Card, USB Flash Drive, and EEPROM. SD and USB Flash are easily removable and readable via computer, they also give me storage for logging - BUT they consume lots of precious memory space with the libraries that read / write. It might not be an issue... EEPROM is inexpensive, but not so easy to unplug and connect to the computer to update the configuration. I need to keep thinking on this one to determine a) how important is logging, and b) how would an end user that isn't an arduino coder update their car's configuration...


Tools:
Power Supply - I've been wanting to get a selectable voltage benchtop power supply for some time. I'm sure there are less expensive options, but I'm eyeing this one from SparkFun. Once it cools down a bit, I want to setup one of my garage workbenches properly to be able to  work in the garage on this stuff without creating  a room full of wires & parts.

Logic Analyzer - The more I'm learning, the more I want to be able to troubleshoot faster and see what is happening at a lower level. Adding tons of debugging Serial.println() statements and reflashing the arduino program gets old fast. I've learned about logic analyzers and want to get the analyzer from Saleae Logic. I think this will also be a great way to learn more and to help my sons see how digital circuits work.

Inexpensive Oscilloscope - Never owned one, always wanted one - this portable o-scope is a great start without spending $2k :)

Books:
I purchased "Make: Electronics - Learning Through Discovery". I think it will be perfect for teaching the boys in a "lab" type setting. The book has a great line on the cover "Burn things out, mess things up - that's how you learn."

I also grabbed "Practical Electronics for Inventors". I've looked at it a few times before, but wasn't ready. Now that I need to go deep into some MOSFET circuits, I'm ready to get more into the theory and try to do it right. Should be a good way to kill some upcoming airport / airplane travel time.

Not a book, but still interesting, I've been reading the Atmel ATMEGA 324p (cpu in the gator+ board) documentation. Now that I've worked with Arduino-compatible boards for a while, it is interesting to see the process schematic and go one level deeper. I might have to get out my microprocessor design book from  my Computer Science degree - that was one of my favorite classes. Yes, I am a geek in case that wasn't brutally obvious by now.