need a circuit diagram for interfacing relay with microcontroller

[nirmal kumar]

my project is about controlling a two 12v,3 amps DC motor with help of relay connection using 8051...
the output pin of 8051 is given to relay circuit of one DC motor and like wise another output pin of 8051 is given to relay circuit of another DC motor.. spec of relay is 12v and 3 amps .. pls tell me some suggestion ... thanq in advance

 

[nirmal kumar]

oh .. then pls give me the circuit diagram of it.. if u have ..

 

[tpetar]

You need firmware or circuit? Suggestion is for relay or circuit?

 

[nirmal kumar]

both if u have ...

 

[tpetar]

Connecting relay to uC can be done like thise examples :

 

[nirmal kumar]

thanq... but in first diagram they didnt mention abt wat type of transistor and wat type of relay .. :/

 

[tpetar]

thanq... but in first diagram they didnt mention abt wat type of transistor and wat type of relay .. :/

It is NPN on first circuit. You can use any NPN like that from circuit, but should pay attention on relay coil current.

You should choose relays with higher resistance of relay coil, this means lower current and consuption and also transistor will have easy job to handle. Example for 12V power supply, relay coil resistance is 300R, you have that relay coil consupt 40mA and for that you must choose appropriate transistor to hande 40mA. For that low current can be transistor in TO92 case, on example BC547....

 

[nirmal kumar]

k .. but i need to control a 3 amps motor then how ll i use 40mA relay ..

 

[tpetar]

k .. but i need to control a 3 amps motor then how ll i use 40mA relay ..

This is relay coil needs of 40mA to energize relay, but relay contacts can handle much more current, that depends from particular relay specification and model, on example 10A or higher, if you whant you can control 220V motors with small relays.


See this :



He can control up to 15A.

 

[nirmal kumar]

thanq ...

 

[tpetar]

No prob. I think you can find nice project in Elektor for this. Or You can just google search "8051 motor control circuit" or similar to this.