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Activate Relay with Digital IO


#1

My hardware guy has selected a relay that is activated with 3 volts and minimum of 70 mA. He suggested that it would be best to have the output at least 100 mA. Can a digital IO pin from my Cobra II work for this?


#2

no, you will need to use a transistor


#3

Thank you. I will pass this on. He thought we might have to do that.

Another question sort of related. We’re converting 13.5 volts to a 5 volt digital input to the Cobra II. Is there a current range that the input must be within?


#4

You have to sum up all power consumption that should give you an idea on the minimum value.


#5

Sorry I don’t think I was very clear with my second question. My hardware guy wants to use this IC to output 5v on detection of 13.5v. The specs says it will output the 5v (Vcc) at 50 mA. Is this ok for the Cobra digital input?


#6

Oh sorry. For digital input it is enough, double check if it is 5v tolerant though.


#7

Check LPC1788 Datasheet for tolerance and current limits of the pins.


#8

generally, digit inputs require very little current. 50ma is significantly more than is required.