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[SOLVED] Relay interfacing problem with uln2803

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Prashant_vaghasia

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I m facing proble to interface relay with uln 2803 in 8051.when relay connected via 8051 pin goes low.
 

Prashant_vaghasia

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please give more information. What pin goes low and when. A schematic would help.

Brian

this is my diagram, my friend.


---------- Post added at 04:27 ---------- Previous post was at 04:25 ----------

please give more information. What pin goes low and when. A schematic would help.

Brian

this is my diagram, my friend.

In this figure microcontroller pin goes from 5v to 0v
 

bigdogguru

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Your schematic lacks sufficient detail.

The following is an example Relay to ULN2803 Interface:



I have also attached a PDF for a 4 Relay Board using a ULN2803 which has a schematic.

BigDog
 

Attachments

  • relay4board.pdf
    2.7 MB · Views: 68

betwixt

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Sorry for adding this warning Bigdogguru: Pin 10 of the ULN is a common connection to all the internal catch diodes and should be connected to the same supply voltage as the relay. I'm just stating this so the original poster doesn't treat it as a 5V supply pin which can have disastrous consequences. If he is using 12V relays, connect pin 10 to the same 12V line.

Brian.
 

alexan_e

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Sorry for adding this warning Bigdogguru: Pin 10 of the ULN is a common connection to all the internal catch diodes and should be connected to the same supply voltage as the relay. I'm just stating this so the original poster doesn't treat it as a 5V supply pin which can have disastrous consequences. If he is using 12V relays, connect pin 10 to the same 12V line.

Brian.

Actually the common pin is pin 9 and not pin 10

Here is another schematic showing the relay connection to a ULN2003

ULN2003_relay.jpg

Alex

EDIT

Please ignore what I said, in ULN2803 the common pin is PIN 10 as you said

Alex
 

bigdogguru

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@Brian - No problem, point taken.

The following are a few 12v Relay examples to reinforce Brian's point:



BigDog
 

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