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Oliver Sedlacek
02/10/14 01:37
Read: 935 times

#190270 - Mostly there
Responding to: Aamir Ali's previous message
In the logic high state the AT89C51 lets the pin float (i.e. IOH is omA), so it is just pulled up by both the 10k SIP and the 4.7K of R3. You don't need both, but you do need a sufficiently low resistance to turn Q1 on fully.

The base of Q1 loads the network, which is why you only see 1V at the pin when it's logic high. There is nothing wrong with this.

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      

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