CS 3651 - APIA - Using a Darlington Pair to make a touch sensor

[CrazyOkanTv1]

nice

[NIKOSGEOR]

Nice... tried with two 2n2219 transistors one LED and 100K and 1K resistors as the diagram says. It works but as expected this is a basic circuit and it is a bit sensitive to human proximity

[EMMEERRE]

Should be the schematic of a Darlington, so 2 transistor in a package whit a really hight gain so should be possible to use just a single transistor

[ejdave2]

why the 100k resistor?

[nirmalGatech]

@mrshko I should add a disclaimer that commercial hardware developers should not use these videos as reference designs...

[mrshko]

Nice idea, but this would never pass in the real-world for a commercial based option. Add a little ESD (static electricity) ~1KV (you wouldn't even notice it) and pop! Better to use capacitive sensing and look for a change in the RC discharge curve.

[deejayspinz]

Thx! Does anyone know if this circuit could be modified to allow for the switch to remain on after you remove your finger. So, touch once, remove finger, but LED stays on. Touch again, remove finger and LED goes off?  If so, how?

[mrshko]

Use a t flip-flop

[mrshko]

Use a t flip-flop



[EwokMatt]

Thanks for your great explanation. You said the first transistor could be a 2n2222 but what about the other one?

[idanbeck]

@EwokMatt The transistors can be the same or different, regardless the resulting current gain will approximately B1*B2 + B1 + B2 where B is the current gain of the transistor.

[idanbeck]

@idanbeck err sorry, it WILL be B1*B2 + B1 + B2

[Xleptix]

hey that's pretty cool. Im a biomed (well in tech school to be one) in the airforce i think i will make one of these today.