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Using a transistor as a 0Volt switch

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joshua17ss2

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will a simple tranasistor act as a zero voltage switch (on/off) with out any additional power other them the pulse from the microcontroller?


i want to use it to trigger a sound board that only needs to pins shorted together to run. i want to make a very simple transistor based cable to accomplish this.
 

crutschow

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You need to know the voltage, polarity, and current of the two pins you are shorting together. You can measure those with a multimeter.
 

joshua17ss2

New Member
as far as i know there is none, just acting to close a circuit if any the chip only runs on 5 volts so the current and voltage that could reach the chip are time.
the default setup has nothing more then jumper shorting the pins.
 

crutschow

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There has to be some current flowing when you short the pins, even if it's small. Just set a multimeter to the current mode and measure the current between the two pins.
 

MikeMl

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There has to be some current flowing when you short the pins, even if it's small. Just set a multimeter to the current mode and measure the current between the two pins.
And measure the open-circuit voltage between the pins with the jumper removed, but with the device power-up.
 
A transistor needs a small current through the base emitter junction and a votage at the collector higher than the base term, (NPN) if all you need is a mechanical connection, then a transistor operating a small reed relay, as someone else suggested would be the best choice.
 

Grossel

Well-Known Member
will a simple tranasistor act as a zero voltage switch (on/off) with out any additional power other them the pulse from the microcontroller?


i want to use it to trigger a sound board that only needs to pins shorted together to run. i want to make a very simple transistor based cable to accomplish this.
I'm not really familiar with the problem, but here's my guess on a solution:

If the voltage level that you want to measure above 0 volts tend to rise relatively quick, you can always bias the base on the transistor so that it's just below the level where the transistor begin to conduct. Then put a cap betwen the base and the signal source. Whenever the signal source raise, the transistor will conduct.

The cpasitors value together with the biasing resistors will determine how fast the signal source must rise before transistor will start to conduct.

I don't know what type of signal you expect to have on the input. If the signal is full of noise, you might add a schmitt-trigger (abbreviated ST) after the transistor. Then you'll need a pullup resistor Rc to feed the ST.

If you dont need any ST (say you have a near sinus signal), then you cold use the circuit below:
Description of circuit here

Just replace dip switch with your transistor.
 
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