computer controle

[hazzyb]

hello every one,

I have been looking around on the forum to see if I can find the answer to me problem but can't so thought I would just ask!!

I need to amplify the signal voltage from me control board to power a small relay I know I need to use transistors but can anyone give me a circuit diagram how to do this?

I know I can get stuff off the shelf to do it but I would rather build my own so I can learn how it all works.

the board has an output off 3v so need to ramp it up enough to power a miniature 12v relay.

just had a though on this, I was looking into using a velman 10 channel kit so if I could get smaller relays, 3v ones could maybe use them to connect to the transmitter, would this work instead?

think I need to do more research..............and go up into the loft and try find all me collage notes and start reading

any help would be good though!!

thanks

Ben

[Joe]

Here's a circuit for driving those relays. These are the parts and why they're there:

2N3904 Transistor: This is the transistor of course, the 2N3904 is a general purpose NPN transistor you can find almost anywhere.

Flyback Diode: when you shut off the current to the relay the coil lets off a pulse of energy. This diode grounds the pulse back to the relay coil so it doesn't hit the transistor or worse the microprocessor. Just use a general purpose diode... like the 1N4000 series. (1N4001, 1N4002, 1N4003,..., ..., ...,)

Steering Diode: This prevents the 12 volts flowing to the transistor from feeding back into the microprocessor. Again, use a 1N4000 series.

Current Limiting Resistor: This limits the amount of current the transistor draws from the microprocessor. I'd try about 5000 ohms. Go lower if the relay doesn't respond, and higher if you can do so to limit the draw from your microprocessor.

[hazzyb]

thanks for the info Joe,


half to order the bits then give it a go!!

Ben