using relays with micro-controller

• Apr 7, 2012

• #1

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hossam abdo

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Hi all

I use a relay with micro-controller.

Can i connect the relay directly to the microcontroller?

when i do that, and out (1) on the micro pin , the relay make somthing error...

 

• Apr 7, 2012

• #2

alexan_e

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The microcontroller can't drive directly a relay , you have to use a transistor as a switch.
In simulation it should work becasue the simulation model doesn't have the real mcu current limit.

 

• Apr 7, 2012

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hossam abdo

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can i use uln2803.
when i use it, if i give the condition to energize it, it energized and de-energized fast without changing the condition.

 

• Apr 7, 2012

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alexan_e

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Yes you can use it, 2803 and 2003 are almost identical

https://www.edaboard.com/threads/246431/

 

• Apr 7, 2012

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hossam abdo

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i cant put the com of the uln2803 as same as relay because of the relay is connect AC power

 

• Apr 7, 2012

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alexan_e

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This image shows just the connection of the coils not the outputs which are connected to the mains

Maybe you can post your schemetic

 

• Apr 7, 2012

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hossam abdo

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that i what I did, but the same error occur

 

• Apr 7, 2012

• #8

alexan_e

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What does the error say?

 

• Apr 8, 2012

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hossam abdo

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when i give the order to energize the relay, it is energized and quickly de-energized and come back energized and so on until I cancel the order.

It behaves like that

 

• Apr 8, 2012

• #10

alexan_e

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Then there is something wrong with your code, I think you use the same button to turn on/of the relay so it oscillated, try adding a delay.

 

• Apr 8, 2012

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hossam abdo

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Dear Alexan
another question:
if i want to turn on 1710 high power led (10mA) with a power supply of (6V & 4A), what is the most appropriate way to design it?
thanks a lot for your help

 

• Apr 8, 2012

• #12

alexan_e

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10mA a power led?
A 10mA LED can be connected directly to the output of the AVR (5v) using a resistor to set the current , there is no need for a separate supply.

 

• Apr 8, 2012

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hossam abdo

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I need to turn (1710) leds on , not one led

 

• Apr 8, 2012

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alexan_e

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How are they connected to eachother?

 

• Apr 8, 2012

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hossam abdo

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i want to write 3 words in area of (100cm * 50cm) with (570 led) for each word.
what i want to know , the best way to connect these leds to reduce the consumed power
as the available power supply is (6v, 4A)