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need help in " realy interfaced with parallel port " circuit Answered

Hi my friends

my teacher  asked us to make ptoject with parallel port
I fount this circuit in this site


and I have some questions about it

now he used in the circuit a 12v relay .. while he's getting a 5v from the parallel port input pins
in that case he used a 12v power supply
* If the relay was a 5v relay .. I wont need to use any external power supply ?
and why he is using the IC here ?

also in the components there was ( ribbon wires ) are we going to use them between the circuit and the male connector ?
another question is how we connect the relay to work as the bulb switch
can I use the 120v bulb that we connect it to household and replace its switch with the relay ?

finally what can I use to connect the parallel port to my laptop USB ?

I know I've asked alot of things but please help me 



Best Answer 5 years ago

The parallel port doesn't supply 5V, so you need to supply the relay from something else, yes, it could be 5V.

The ULN2803 datasheet will tell you all you need.

The circuit you've shown shows EXACTLY how to wire a light to a relay.

And you need to find a USB- parallel adapter cable.

I've said it before, your teachers are WAY behind.


5 years ago

don't tell about the teacher -_-"

so now the parallel port just send the signals either 1s or 0s to our IC

about the bulb circuit I ment that even I used that high of voltage it will work fine because the two circuits are totally independent right !

thank you alot mr.steve ^^


Answer 5 years ago

With the relay, yes, they are totally isolated - if you wire them carefully !!


Answer 5 years ago

OK I'll do it first with low voltage to test it

thanks for reply