Friday, January 29, 2010

Once again, we have learned that I am good at breaking things. In fact, I usually learn best when something ends up broken. That way, I know not to do it again. This time, I managed to fry the logic board in the Open ReVolt "Cougar" Controller. It all stems from hooking up a tablet computer to the controller to use for reprogramming and data-logging. I got the tablet computer for free, but it doesn't have a battery. Instead, it needs to run from 12V DC to a 12 to 20VDC converter, and into the computer. I didn't realize that the RS232 port has so much grounding in it, and I somehow managed to push over 20 volts to the ReVolt 12V in. The other night, I got to stop over at Tom's house (for Robot Night) and I pulled out the multimeter and soldering iron to figure out exactly what parts I broke. We tracked down that R1 and D2 were both smoked. R1 was easy to replace, and the controller can work fine without D2, as long as you have a known good voltage going to the controller. Further bench testing showed that the ATMEGA chip was either fried or had a bad case of amnesia. Fortunately, I had a spare one of those from when I did a software update a while back. UNfortunately, replacing the ATMEGA chip did NOT make the controller work properly again, although it does seem to prove that everything on the POWER board works fine, it's just the LOGIC board that's all messed up. The 12V DC/DC converter tested out OK, as did the doo-hickey that converts 12v to 5v. However one or two other 5v components may be bad, and I have no really good way to test them. Paul Holmes offered to help me out by mailing me some spare parts, and possibly even soldering up a fresh logic board. So, my car isn't running right now, but I sure am learning a lot by poking at electronics with multimeters! Another thing I learned about the Open ReVolt controller that I thought is kinda cool is that it's much easier to bench-test than, say, a Curtis controller. For example, a Curtis controller usually has come sort of voltage range, like 48-72V. That means you need at least 4 batteries just to power the thing up (if you, like me, do NOT have an adjustable bench power supply.) You then need 4 12V light bulbs, or a spare motor, or something similar to use as a test load. It starts to be quite a setup. On the other hand, the ReVolt only requires a 12V battery for logic power, and almost any voltage you want for the power section. The test load can be a single 12V light. All I needed for bench testing was a 12V battery and lightbulb, a few jumpers, and a pot. That's it! Even I can handle that. More next time, once I get this thing on the road again. -Ben

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