January 9, 2010
I'm sure many of you have been in the situation where you are making some simple part for your robot, it should be an easy job, maybe 15-20minutes tops but something goes wrong. 3 frustrating hours later (or more) you finally get it finish after trying to work out what went wrong.
It's 10:30pm on a Saturday night, I've been in the office since 11am making an Xbee remote control for demonstrating the 6WD robot chassis so we can make a video. I should have been finished hours ago and relaxing in front of the TV but I couldn't get a LM317LZ regulator to put out 3.3V for the Xbee.
At first I though I'd made a mistake since it is all made on a Mr. Basic protoboard. I double checked every thing, even measure the resistor values just in case.
Ok, I must have overheated the regulator when I soldered it since it is one of those tiny little ones only rated for 100mA. I replace the regulator and get the exact same problem.
I get on the net and check my datasheet against others from different manufacturers since I have been caught out with a misprint many years ago. Nope, all the same.
I rebuild the regulator circuit on a breadboard with another new regulator, same problem, output voltage too high and getting far less than the 1.2V I am supposed to get between output and adjustment pins.
I finally swap out the LM317LZ (TO-92 package) for an LM317T (TO-220) which is basically the same regulator but with a 1.5A rating.
BINGO! it works, put in another LM317LZ and damn, 4.2V instead of 3.3V again. Fortunately I had tested the power before plugging in my Xbee otherwise it would have been smoked.
Seems I wasted about 3 hours to determine we have a bad batch of regulators (about 20 of them). Finally I finished the transmitter. Wonder what fun awaits me with the reciever???
Above is the bought controller I raided for the joysticks, below is my prototype Xbee controller.