Email: Password: Remember Me | Create Account (Free)

Back to Subject List

Old thread has been locked -- no new posts accepted in this thread
Aamir Ali
02/09/14 10:00
Read: 2251 times

Msg Score: +1
 +1 Good Question
#190268 - Interfacing 12V relay with AT89C51
1. I have to interface 12V relay & used circuit used is:

I have used R2=1K & R3=4.7K. Relay is operating fine but I have seen my pin gets loaded. Link says R2 can be avoided also. but i used for safety.
When logic is +5V at AT89C51, due to loading voltage across it reduces to 1V or less.

What should be correct values I should select.

2. I have to connect relays to PORT0 also. Now for using port0, first I needed external 10K sip after which I will connect the circuit. Is this correct??

Because I think this created two pull-ups across port0. One is 10K from sip & other is 4.7K(R3). Should I remove 10K sip from port0 in this case.

3. What should be max IOH & IOL for AT89C51.
I was reading:

On Page 10, maximum Iol per 8 bit port is 26mA(port 0) & 15mA other ports.

What should be Ioh per port or per pin

List of 4 messages in thread
Interfacing 12V relay with AT89C51        Aamir ALi      02/09/14 10:00      
   Mostly there      Oliver Sedlacek      02/10/14 01:37      
      Then what do to avoid loading??      Aamir ALi      02/10/14 04:23      
         Pin doesn't pull up      Oliver Sedlacek      02/10/14 05:51      

Back to Subject List