Bad Day

Posted by Erin, the RobotGrrl on Thursday, August 7th, 2008

It was a pretty bad day at my research lab today (aka: my desk next to the kitchen table, the kitchen table itself, and the floor) xD .

I was playing around with the Pololu uSSC’s, they were working great after I set the servo numbers!

But, I was a little troubled by two things.
1) When the program is sent to the Arduino, the Pololu uSSC gets a fatal error because of all the goobley that goes on the TX line when transferring the program to the ATmega.

2) When I pressed on the servo, the voltage drain was visible when the boards flashed on and off

For the first problem, I tried so many things with switches and crazy circuits … but it didn’t work. So I just used a jumper from the Arduino TX to another row where the SIN’s would be on the Pololu uSSCs so that I would only have to unplug one wire instead of two each time I was trying a program. That was OK.

For the next problem, I supplied 3 more volts in the form of two rechargeable AA’s. But… after looking at a breadboard for so long your eyes start to go crazy… I inverted the poles.

It wasn’t even a second later when the board became so hot that I panicked, tearing it out of the board. But, a cloud of smoke lingered in the air. At that time I knew it was toasted… even one of the batteries was smoking.

So at the end of the day, I have one extremely dead Pololu uSSC, one that doesn’t work, and one dead RBBB. I *think* the RBBB isn’t working because the ATmega isn’t working

So… yeah… pretty bad day. The lack of sun week after week after week doesn’t help either. It’s like living in a groundhog hole You get some sun, but once you go out, it disappears.

Posted in: Projects, Robot.
Tags: Arduino, ATmega, bad, blowing up, dead, polarity, Pololu, stupid, ug

3 Responses to “Bad Day”

1. Mike Says:
   August 7th, 2008 at 11:22 PM

   Ugh, I hate it when that happens! Hopefully the damage is easily fixable. Servos can pull quite a bit of current, especially when you stall them. For the next test I’d recommend using separate power supplies for the servos and logic circuits. A strategically placed diode might prevent a future reverse-polarity incident, too! =)

2. Ron Says:
   August 8th, 2008 at 8:18 AM

   There’s a reason why engineers call that first circuit power-up a “smoke test”. It’s like an initiation ceremony.

   I agree with Mike, get yourself a slew of 1N400X series rectifier diodes. You’ll need them for a buch of projects. The X stands for their breakdown voltage (1N4002 = 100V 1N4004 = 500V). And also some 100 ohm resistors. I use both for reverse voltage protection. The diode stops the reverse (up to its breakdown voltage–ALWAYS put in way more than you need–it’s a cheap part) and the 100 ohm resistor, while it does give a current drop, is used to prevent the battery from overheating if reversed (and therefore shorted by the diode).

   There are two things I routinely over-engineer: power supplies (because a bad one can kill you) and inductive load drivers (because motors have a way of killing silicon). I haven’t worked with servos, so I can’t help much there, but for driving regular motors, I’ve used stuff like L298 H-Bridge chips. They can take a lot of abuse (the L298 can handle 40V of motor supply at 4 amps!). David Cook (robotroom) has some great tutorials that are clear and accurate.

3. Ron Says:
   August 8th, 2008 at 8:23 AM

   (The 1N4004 is 400V, not 500V.)

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