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February 25, 2007

LC VI: Testing and fixing

This was my last but one day and I really wanted everyone’s circuits to work before I left least it turns them off the subject totally. There were only two techniques I had to offer to test and fix the circuits: a) Visual Inspection by peers b) Measuring voltages in circuits that worked (and if they were consistent) compare them with the ones that didn’t.

I pointed to Senthil that one of his LEDs seemed backwards. He said that most of them are correct. I told him that even if all but one were backwards it wouldn’t help. Most of his LEDs were not marked and as Perumal looked over Balu’s circuit Senthil pulled out his LEDs and Balu tested them for him and marked them. Balu had understood the connections correctly, but the three leads of the transistor were perhaps too close and seemed to have shorted out. I encouraged him to pull out the transistors and spread out the leads and re-solder them. He did it for one and his LEDs glowed, but quite dull. We measured the voltages and found that one of the node voltages in the other transistor did not match. He then did the same to the other to get his circuit to glow nice and bright. Senthil had not understood something from my explanation, but with a short chat with Perumal seemed all enlightened. He pulled out his complex labrynth of connections and re-soldered them in the way he understood and his circuit worked too. Attached is a pic with each person holding their working circuits out just before I was starting for Chennai.

That evening the kids started preparing a farewell gift for me, the first in-house bamboo Tulir torch which two of them are holding out when they rushed to the bus stop to give it to me.

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