Protoboard servo power not working (protoboard exploded?-fixed!)

bulkhead

see post #4 for new problem

I just had it working and then it stopped. I have the jumper hooked across the middle and bottom (Vin) pin. Now I only measure about .29V or so between the top and middle pin on the servo headers. I do however measure Vin correctly at the jumper point. When I had it working, the servo headers were correctly reading the battery voltage (Vin). What could have happened? It seems to me that there is something wrong with the capacitor and inductor (?). Right now I am considering removing those 2 components and directly wiring the jumper to one of the four servo headers, would this work? Any advice on preventing/fixing this problem would be nice too. Thanks.

Edit: I just measured the voltage across the inductor and it is 8.00. Vin (battery voltage) is about 8.28. That leaves roughly ~.29V on the servo headers. Is this normal?

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I'm new to the propeller!

Post Edited (bulkhead) : 8/4/2007 5:32:15 AM GMT

Skogsgurra

You may have gone beyond the current capacity of the inductor. These small SMD inductors have a very low heat capacity. You can use a few inches of wire (being metric, I would say about 10 cm) coiled up in a small solenoid and connect it where the inductor is connected.

You may also not need it, just bridge the inductor with a short piece of wire. It is with this as it is with the decoupling capacitors, it may run well without it.

Avoid this happening again? Don't overload the circuit. May be a good idea to put a fuse there. Although fuses usually cost more than petite inductors...

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bulkhead

Thanks for the response. I ended up just hooking up a jumper to bypass the inductor completely. It works fine now.

I was only running 2 motors through the 4 servo headers, drawing 2 amps at most (otherwise, my H-bridges would go). I guess I'll just add the jumper whenever I use these motors or high torque servos.

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I'm new to the propeller!

bulkhead

Ok, it worked fine for a while after I hooked up the jumper directly across the inductor and then I mounted the protoboard onto an aluminum case [noparse][[/noparse] see 3 posts down] and when I powered it on, it started smoking! At first I thought it was the inductor because it looked a little funny, but then I flipped it over and saw this:




Is there a diagram that shows where all of the connections are physically on the protoboard? I'm trying to trace the path and figure out what happened. It seems like the motors current need exceeded the capacity of the board. I checked the voltage regulators with a multimeter and they are working fine. At the jumper point where the servo voltage jumper goes (to select from Vin or 5V), I measure correctly Vin and 5V. I currently have the jumper on Vin. The propeller also programs fine, but there's no voltage at the servo headers. Any help would be appreciated.

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I'm new to the propeller!

Post Edited (bulkhead) : 8/4/2007 3:20:49 AM GMT

Mike Green

No, there's no diagram available. You must have some kind of short circuit in your motor circuit since those are fairly substantial circuits. No wonder you were able to blow out the inductor. The power switch is on the right and the power input circuit is way on the left. The #2 trace is the power from the jumper for the servo power source and the #1 trace is the power from the switch to the servos. The mask ink is blistered off which takes a lot of heat ... it normally withstands soldering temperatures.

That's why fuses were invented!

RinksCustoms

I'm not sure what kind of servos you are using, perhaps you have them connected backwards? Are you trying to use giant scale servos? The capacitor is for decoupling, it supplies the servos with an additional bit of current when they make a quick move and prevents the 3.3V supply from getting a brown out condition which will cause the propeller to reset. The inductor forms a low-pass filter so the back-EMI from the servos can't "inject" noise into the rest of the board. I recomend using a separate supply for the servos and use the prop to supply the signal. Don't forget to tie a ground from the protoboard to the servos, so that you have just a mutual ground and a signal going to the servo(s)

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E³ = Thought

http://folding.stanford.edu/·- Donating some CPU/GPU downtime just might lead to a cure for cancer! My team stats.

bulkhead

I three posts ago said...
I mounted the protoboard onto an aluminum case

I found the problem. There was a short from Vin to my aluminum case. The washer I used to mount a perf board touched the edge of the wire poking out of the solder joint adjacent to the perf board's mounting hole. This is why when I tested each time WITHOUT the protoboard mounted to the aluminum case, it worked fine. However, as soon as I mounted it, it created a short, and then continued to burn out the protoboard's connections. I finally hooked up a jumper directly from my battery to the servo header on the protoboard in an attempt to get it to work, which resulted in my discovery of the short. All of insulation the wires on the way to the short point started smoking and melting I didn't my battery think could do that...Mike, I'm going to look into those fuses!

Lesson learned: Test connections not just before, but AFTER mounting boards, especially onto a grounded frame!

Alternate lesson learned: Don't ground the board onto the frame? This seems like the easier and most logical solution; just don't have a large conductive structure hanging around to cause a short.

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I'm new to the propeller!

Post Edited (bulkhead) : 8/4/2007 3:21:44 AM GMT

Mike Green

Sometimes it's very useful to ground the board to the frame, like for shielding. You have to be very careful to inspect spacers, washers, screw heads, and adjacent wires as you discovered. Pick your screw sizes so the head, spacer, washers, etc. fit within the "footprint" of the mounting hole.