Relay Question

[holdit]

Hi
have a 16f628a pic going to a uln2003a that controls 3 dpdt relays
relay 1 controls fwd / back motor1
relay 2 controls fwd / back motor2
relay 3 is to control which motor to control etc...
as in picture attached
eg: turn relay 3 on and relay 1 on and motor 1 turns fwd
i could do it with relay 1 and relay2 and 2 spst relays but i have only these 3 relays

any help????
MOD i did post this in a similar thread but it was better to start a new thread

 

[bananasiong]

You can use the third relay to control either of the supplies (Vdd or Vss) of the other two.

 

[holdit]

problem is that relays are now on board (silly me) but will that work if relay3 is dpdt as there is no off postion? iam blank here lol
any easier way

 

[holdit]

i think i can remember a way with a common return and using a diode but cant remember correctly
any ideas?

 

[bananasiong]

Since you're using relay 3 to select either relay 1 or relay 2, either SPDT or DPDT will work.
A diode is used to protect the transistor that switch the coil.

 

[holdit]

thanks for reply
iam using a uln2003a with diodes in
but i was thinking there was a way to use a diode to reduce wiring for forward and reverse cicuits an old model railway trick but i a cant remember now
anyway is posible to have a diagram/instuctions of how relay3 could control relay1 or 2 apart from the vss vdd
thank you

 

[shokjok]

Relay 3 could be used for direction control, or as a pulser as in a blender motor or pool pump. It can also be used to feed the two existing relays, or a third motor.