DIYEFI.org Forum

Went on vacation for a couple of weeks, so haven't made much progress on this project.
However the first batch of boards arrived while I was gone, I'll include some pics.

Might get a chance to put one together in the next couple of days, I did it backwards from what I should have done I think, I built the small one first when I probably should have designed a larger mostly through hole design, but the small dude just seemed to hold my enthusiasm. The board uses mostly 0603 sized components, those and all but 1 chip are fairly easy to hand solder. The 5volt regulator I chose is a different story though..... It only comes in a 12WSON package ( kind of a PITA ). However it has very good specs, weather it was worth using or not remains to be seen, I tried to keep the digital and analog circuits somewhat separated, but as this design uses the Atmels ADC that is referenced to the Vref it may be fudimentally limited, only way to tell is to test it once it's assembled. I could have just used the regulator that is already on the pro-mini board, however that one has pretty dismal specs and would most likely suffer thermal issues at the higher voltages it will be supplied with.

Sorry, loaded two of the same pic, here's one of the top

Neat stuff! :-)

Got one board assembled. My plan was to use solder paste and throw it in the oven, but someone at work threw out my tube of past so I had to go old school on it. The voltage regulator was a bear, and didn't align as well as I wanted it to but it does appear to be working, now to wire up the O2 sensor and load some code into the arduino pro mini.....

I did some initial testing, doesn't look like it will work "out of the box" with the code provided by Hellfire.

I am just using a serial com window (arduino IDE) to monitor the controller. I'm getting wildly varying values from most of the ADC Chanel's, and while the heater control does appear to work I'm not getting anywhere near the temp from the sensor that it needs.
I played around with some of the values in the code and was able to get the O2 up to a temp that should start to read, but the values coming from the ADC channels was still all over the place. I need to try removing R5 as was suggested and see if that helps, however without some guidance from Hellfire on exactly what the code is doing ( I can make guesses on most of it) it's hard to know what might be going awry.

It may also simply be a ground issue, on the board I kept the high current heater ground and the low power logic and analog ground separated, but I put a jumper to connect them right at the power connector, I need to remove that jumper and see if that helps.

On the plus side though, the heater control MOSFET remains quite cool ( it has very low RDSon ) and the 5v regulator also seems to be doing a great job. If I get some free time at work I will try to get a scope on it and see if I can shed some light on what is actually happening.

Cut your jumper and burn it as a sacrifice to the gods of grounding strategies. Then ensure that the wire for heater ground is sufficient to ensure you can still reliably switch the FET.

LOL, I'll give that a try. It's a solder jumper so all I need do is swipe it with my iron, I'm thinking a 9 iron will do the trick.

I put it there on purpose, not knowing how much effect the high heater current might have on the ground plane I thought it would be a good idea to separate them.

Better yet would have been to separate the analog and digital planes, not sure how feasible that is with such a tight board, but if I can get this to work that will be the main focus of the next board revision.

Board design stuff is important once frequencies and currents get up there, however more important is separating current paths and ensuring no V drops on critical connections. Keep it up! :-)

Fred.

This is an interesting project and I want to congratulate on the initiative.
I wonder if there is any update ?

Hello all.
I wonder has this project made forward steps ?
Thanks ?