Go Down

Topic: Transistors (Read 351 times) previous topic - next topic


The LED has built in current limiting?

No technical PMs.
The last thing you did is where you should start looking.


Jul 17, 2017, 04:15 am Last Edit: Jul 17, 2017, 04:17 am by Jiggy-Ninja
Can you at least try to lay out your circuits in a sensible top-to-bottom order with a minimum of overlapping wires like TomGeorge did? Both of the ones you've posted make me queasy with all the flips and spins (literal mental gymnastics) I have to do in order to get things in a more sensible arrangement. Your schematic would take many minutes to unravel and decipher, whereas with Tom's it takes about 3 seconds to see what's going on.

When you lay out your schematic properly, you'll be able to avoid embarrassing mistakes like not knowing which components are connected to which ("No no, Tom, the 220R is to pull-down the first transistor's base." when that resistor isn't even connected to Q1's base) and see that there's no actual feedback (the characteristic "criss-cross" that I'm sure you've seen) between Q1 and Q2 like in a real astable oscillator.
Hackaday: https://hackaday.io/MarkRD


The bottom transistor can not turn on at all, emitter voltage higher then base.
The LED was not on at all.
The bottom transistor will turn on. BJTs work when emitter and collector are switched but with worse parameters. Current from base to collector will open the transistor so current may flow from emitter to collector.
If I understand the schematics right it may oscillate relying on parasitic capacitances etc. But I believe much more probable result would be both transistors half open and no oscillation.
On 8-bit (i.e. Uno) use "byte" instead of "int" if possible - it is faster and saves resources!


Jul 17, 2017, 02:54 pm Last Edit: Jul 17, 2017, 02:54 pm by TomGeorge
Updated version, my interpretation.

Tom... :)
Everything runs on smoke, let the smoke out, it stops running....


That almost looks like something familiar, but I just can't put my finger on it.

Still don't think it's an oscillator.
Hackaday: https://hackaday.io/MarkRD


I looked around, reminds me of  transistor equiv of triac or scr, but they don't have resistors and one is PNP the other NPN.
(WOW that was a bit of a timewarp...  Electrical/Electronics class at uni.)

Q2 orientation has me worried.

Tom.. :o
Everything runs on smoke, let the smoke out, it stops running....


Jul 17, 2017, 04:10 pm Last Edit: Jul 17, 2017, 04:12 pm by Jiggy-Ninja
That must be what I'm thinking of. I knew it wasn't an exact match, that's why I said "almost".

So Q1's a common collector amplifier and Q2's doing...something useless like usual.
Hackaday: https://hackaday.io/MarkRD

Go Up