Transistor choise for PICAXE08M?

[Andrei Reaboi]

Hi guys.
I was rying to connect 3v relay to my PICAXE08M. Relay would only twitch a small bit and thats it, and then i realised that i need to connect it using transistor.
What kind of transistor would ye recomend using.?
Thank you.

 

[Andrew Cowan]

I would use a BC639 as a low side switch. Remember the diode (1N4001?) to absorb back EMF.

A

 

[Andrei Reaboi]

I would use a BC639 as a low side switch. Remember the diode (1N4001?) to absorb back EMF.

A

is that diode for the coil of the relay?
Thanks andrew

 

[Andrew Cowan]

Yup. The side of the diode with the stripe should be attached to the positive rail.

A

 

[mikie_121]

Just about any of the small NPN transistors will work. BC337,338 (800mA) or 546,547,548 (max current of 100mA) switching ground to the coil.

 

[Andrei Reaboi]

Will 1K resistor be enough for the base of the transistor if im using 5V for my PICAXE?
I think 1K is normaly being used but might be wrong here.
Cheers.
Also, does any one have general diagrams on how the relay should be conneted using all nessesery diodes, transistors and resistors.
I have it all in my head but just strugle a bit with the final assembly.
Thanks again.

 

[russbow]

Have a look at the picaxe manual, page 23, second diagramme.
Just substitute your relay for the solenoid.

1k resistor should be fine. For the transistor, I dig in my junk box and find a BC548, ZTX500 or BC107 - not critical.

 

[Andrei Reaboi]

Have a look at the picaxe manual, page 23, second diagramme.
Just substitute your relay for the solenoid.

1k resistor should be fine. For the transistor, I dig in my junk box and find a BC548, ZTX500 or BC107 - not critical.

Cool, thanks, missed that diagram while flicking over.
Cheers again.