Transistor as an analog input

Question

If i were to use a transtor as an analog input device is that the proper way to connect it to the arduino? Thanks!

billabott · Accepted Answer

"... what is that resistor before the 5v ... ?" Good question.

As the input signal increases and current, I(b), begins to flow out of the base; a much larger current, I(c), flows out of the collector and that current, my friends, creates a voltage drop across R(c) which the 'Duino will sense on its analog input pin, Ain. Just to make it clear, yes, the output signal is amplified but also inverted.

Oh, and by the way, taydaelectronics.com has some very attractive prices on PNP and NPN transistors. See their facebook page for frequenct coupons to help pay part of your S&H charges.

billabott · Answer

I positively agree. N.B. Signal will be distorted due to the fact that the emitter base junction will be OFF whenever the input signal is below 0.7 volts.

billabott · Answer

The data sheet for the transistor will have a max. I(c) value. Reduce by one half and you have R(c) = 2* [V / I(c)]. Via the Application of Ohm's Law : V=I*R. The R(b) will be about 100*R(c).

Say, dirtdriver, where do you go to school anyway?