I have built the circuit below, when connected to the pic the relay
operates regardless of the pic pin being high or low. I have also
noticed that the relay energizes if I place the base through 2.2k
resistor to ground or vcc. Any suggestions?


Regards,
Steve

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Herbert Graf
Sent: Sunday, January 27, 2002 12:26 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]:Driving a relay?

Yes, quite easily. IIRC most typical PIC pins can source 20mA (although
there is a device limit as well to consider). Assuming a 5V supply one
of
these circuits would draw: (5V-0.7V)/2.2k =~ 2mA, so theoretically you
could
drive 10 of these circuits from one PIC pin! :) TTYL

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Steve Kasm
> Sent: Saturday, January 26, 2002 22:21
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [PIC]:Driving a relay?
>
>
> Hello All,
>
>
>
> I need to drive a relay from a pic pin. I know how to do this with a
> 2.2k resistor to the base of a NPN transistor with the emitter to
ground
> and the collector to vcc through the coil on the relay. I have also
> placed a diode etc in the circuit in the circuit reverse biased across
> the relay coil.
>
>
>
> My question is that I need 2 identical relays to pull up off the same
> pic output pin. Can one pic output safely drive 2 of the above
circuits?
>
>
>
> Regards,
>
> Steve
>
> --
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