Aromatherapy

Today's lesson: burning resistances is therapeutic.

Today we burnt two during the mini-projet session. The mini-projet is an electronics project where we have to come up with a circuit, depending on the topic they give us. We prepare it (the theory) in advance, then we have three 3-hour sessions to put the circuit together, test it, and correct anything.

Our topic was to make a 15-volt direct current generator, using the EDF power supply (EDF = French electric company). The generator had to have a protection system against high currents (maximum 400mA). We had a transformer, and we could use operational amplifiers, diodes, transistors, resistances, capacitors,...all the basics. (these details are for those who happen to specialize in this field) So we came up with the circuit; we simulated it and everything worked really well.

And here's how our three sessions went (I won't list out all the details, otherwise it'd be very, very long!):

First session: We put everything on the board, but we had a problem measuring one of the voltages, and the teachers were too busy walking around talking to every group (we worked in pairs) to come and help us :/ So we didn't do much, but at least all the electrical components were already placed on the board, ready to be used the next time. (it's not that easy, we had to be really careful not to get all the components mixed up, okay!)

Second session: We found out that our problem was (simply!) due to a faux contact ⁽¹⁾. So we went on to test the rest of the circuit, which worked pretty fine except for a few problems that were solved pretty quickly with the teachers' help. (there were more teachers there during the second session) And then, the highlight of the session: we tested our protection system (by using a small resistance as the charge) and we saw smoke! So we quickly cut the power (bien sûr, on voulait pas tout faire exploser ⁽²⁾ :P) We tested our circuit with a "normal" charge and it worked fine, so we were wondering what was smoking, cos if it was the charge, who cares? :P All we needed to do was protect our circuit, not the charge. So we asked the teachers (two of them, with different opinions :P), there was some blah blah blah, and we ended up putting a heat dissipator on one of our transistors. End of session. (so no time to check whether the dissipator solved the problem)

Third session: We were pretty hard-pressed to be done, 'cos that was the last session and we had to present our circuit by the end of the session. After a few tests with different charges, we decided that the smoke from the last session didn't come from the transistor, but from the resistance that we used as the charge. So our circuit worked; we just had to cut the power pretty quickly when we were using a small resistance. (we could smell it burning even before it started smoking)

But, during the presentation the teacher (Claude Richard ;) ) didn't want us to cut the power...he went "c'est pas grave ⁽³⁾ ", "c'est pas cher, un transistor ⁽⁴⁾ ", "c'est grave quand ça brûle et on sait pas pourquoi ⁽⁵⁾ " (et on savait bien pourquoi! ⁽⁶⁾ ;) ) Everyone around smelt the burning odour and at the end the whole resistance was black and smoking (it was as if there was a miniature bonfire on our circuit board! We could use the smoke for communication with the other tables! :P) Then we put another resistance (a slightly bigger one) and it burnt more slowly, but we still smelt it...it didn't turn completely black though, it didn't have enough time :P

Even the other teacher who was evaluating us (they came to evaluate us in pairs) wanted to cut the power when it started smoking...and guess what C.R. said? "Ils ont pas l'habitude, ils font pas ETEP ⁽⁷⁾ " ("ils" comme les autres profs ⁽⁸⁾ )

I'd like to insist: the first burning resistance smelt hor-ri-ble! That's why everyone turned around to see what was going on! That, is our wonderful electronics aromatherapy. C'est en brûlant des résistances qu'on apprend des choses! ⁽⁹⁾ lol

"Glossary"
(1) it's when two pieces should be touching but they don't - dunno what it's called in English, can someone tell me?
(2) of course, we didn't want to explode anything
(3) it doesn't matter
(4) a transistor is cheap
(5) it matters only when it burns and you don't know why
(6) and we knew why!
(7) they're not used to it 'cos they don't do ETEP
*ETEP = Electrotechnique et Electronique de Puissance (electrical as opposed to electronics?)
(8) "they" as in the other teachers
*Claude Richard is one of our ETEP teachers, and also the director of GE (my department)
(9) It is by burning resistances that we learn!

There are loads of terms I don't really know in English, if someone knows them, tell me! :)

Edit: So here's our final circuit!