piclist 2000\01\18\111719a >
Thread: Driving Relay
picon face BY : Jane Ifurung email (remove spam text)

I'm using a +5V DPDT relay and I had a problem with
regards to energizing its coil. I tied one end of its
coil to +5V and the other end to an AND gate output
(MM74C08N). The relay should be energized when the
output of the AND gate is logic 0 and deenergized when
logic 1. However, when the AND gate is supposed to
output logic 0, it always stays to logic 1 (this is
when it is connected to the relay). Does this mean
that the AND gate is being loaded by the relay? ....
sort of loading effect?

I also tried using AND gate buffer (CD4081BCN) but to
no avail. It can't drive the relay.

.... Now, I was able to solve the problem stated
above. At the AND output I inserted a buffer(74F244)
and tied the buffer output to the other end of the
relay coil. It worked!

My question is, is there an alternative solution?
Buffer consumes space.


Jane Ifurung
UP Diliman, Quezon City
920-5301 loc 5854
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See also: www.piclist.com/techref/io/motors.htm?key=relay

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