Quick electronics query to boost signal using transistor

Hi guys, I have a signal that I want to input into a digital input, basically it is just a square wave about 0 to 0.5v, so I think I need to boost it up to around 0-5v so that I get reliable readings by the picaxe of high/low states, I have some 2n3904 transistors here and a 600 odd assorted values resistor pack, so I'm hoping that I can use these to increase the signal so picaxe will see the signal properly.

Does anyone have a schematic for a simple circuit to do this using the parts I have on hand? I have looked around to try to find something suitable but it is a bit hard to know the exact terms to use.

Thanks.

Search Google for this "2n3904 switching circuits" ...

The "0.5" volt square wave may be a problem for a single transistor.

You may be able to utilise the transistor as an AC amplifier, provided the square-wave frequency does not go too low. You would have to live with some phase shift, which may or my not be a problem. We need more information.

Hi,

Is it actually a "square wave" (i.e. equal mark-space ratio) or a repetitive "pulse", or an arbitrary logic signal? If it is a "wave", what frequency (range) has it got? And what about the levels? Does it swing between, say, 0 and 0.5 volt, or with a higher dc bias, or is it ac (capacitor) coupled? Is it a "clean" signal, or might it have some noise superimposed on the levels? Has it a low or high source impedance (i.e. where does the signal come from) ?

Probably you just need to ground the emitter and connect collector to a PICaxe input. But the answers to the above questions will determine how best to couple/bias the signal into the base.

Or, all modern PICaxes have at least one on-chip comparator which can "slice" any signal applied to a pin at a defined dc level.

Cheers, Alan.

This should work but you will need to experiment to find the value for R.

Steve G.

sghioto said:

This should work but you will need to experiment to find the value for R.

Click to expand...

It will be interesting to see a result of such an experiment because that unknown value is very important.

Perfect job for a mosfet, you'd be done already, no mucking around with bias resistors. Grab a bag of 50 for $3 and you'll never go back.

http://www.ebay.com/itm/50x-New-60V-0-2A-2N7000-TO-92-NEW-Arrival-N-CHANNEL-Transistor-/281504886886

It should be possible to use the on-chip comparator hardware if the PICAXE chip has that, even if it means playing around with system SFR's. That would be a zero additional components solution and what I would consider first.

Hi,

+1 to that, hippy. And IMHO this is a situation where a FET (with or without a bias network) is probably not the solution.

But until the OP comes back and explains what is meant by "just a square wave about 0 to 0.5v", we're all just guessing.

Cheers, Alan.

hippy said:

... That would be a zero additional components solution ...

Click to expand...

I like this man's attitude

And if the Picaxe on chip comparator couldn't be set up to do the job I wouldn't use an external FET or transistor but rather suggest the use of an external comparator. It really depends on the application and how accurate the switching (slew rate and levels) need to be.