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How to send a 3V wire low with a transistor and picaxe

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splents

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Hi All,
I'm fairly new to electronics, and I'm still trying to get my head around the transistor concept. I've been struggling with this particular problem for quite a few weeks, googling tirelessly. Finally, I am here, seeking your help.

I need to automate a camera startup with a PICAXE.
The camera turns on/off when the 3V wire running to the button is held low for 2 seconds.

I've attached a drawing of what I've tried. One of many things I've tried, this one seemed the most likely to work... Please excuse its lack of technical correctness.

Any ideas, advice or solutions would be greatly appreciated.

 

To keep the on/off wire low (via a transistor) you have to set pin1 high ..
Program for PICAXE may look like this:

Code: 
Start:
High1
Wait 2    [or Pause 2000]
Low1
End

So, each time you apply 4.5V power PICAXE will generate 2s pulse on pin1 ..

Rgds,
IanP
 

    S

    splents

    Points: 2
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Thanks so much for the reply!

I'm cool with the program side of things, my problem is the transistor setup.
In the rough diagram I sent, would the transistor correctly pull the on/off wire low?
Or am I using it incorrectly?

Regards
Angus (splents)
 

Hi

I don't understand the requirements of the circuit perfectly but as far as transistor use as a switch is concerned - A positive VBE will cause the switch between CE to close and a zero VBE will cause the switch to open.

Now, just replace the transistor with an ideal switch (mentally) and see if your circuit works as desired.. The thing of your main concern must be that you are not creating a short between a voltage source and ground as this might be disastrous..

In your design is the "3V" possibly such a voltage source which could be possibly grounded by the switch?
 

    S

    splents

    Points: 2
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Cheers.

The 3V wire was formally part of the on/off switch. The 3V wire, is grounded by the on/off button to turn the camera on and off.

Your suggestion is completely correct, and so far as I can tell, on that basis my usage of the transistor should have the desired effect.

If I send the 'base' pin of my transistor high, the 3V wire to the collector and the ground to the emitter, I *should* be sending the 3V wire low? But this doesn't seem to be happening. I was wondering whether I have over simplified the problem, or have completely misused the transistor.

And that is the crux of my problem. Hopefully this has removed the ambiguity in what I was asking.
 

Hi

Two problems can be there in your circuit:
1) The output voltage level of PIC is not sufficient
2) PIC is not able to drive the BJT.

So, please measure the output voltage of PIC without connecting it to the BJT input and repeat the measurement with the connection made.. you can post the numbers here so that we may find the problem.
 

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