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TTL gate to 2n2222

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New Member

I am making a little circuit to switch audio sources and it is many years that I haven t used electronic... How do I calculate the value of the resistor :

I hope the design is ok ?
This is only the usefull part of my design.

Thank you for you help.

Nigel Goodwin

Super Moderator
Most Helpful Member
No, the design is completely (and self destructively) wrong.

The relay must be in series with the collector, and MUST have a protection diode across it.

Check out the relay example in my tutorials

Nigel's PIC Tutorial Hardware Extras

The resistor isn't critical, it needs to be low enough to switch the transistor fully, and high enough to not overload the chip.

Try something like 1K for a start.


New Member
First of all thanks for you fast reply.

I did not notice that the design was completely wrong, thanks for make me paying attention that it was completely wrong...

Now this is fixed i would like to ask you another ting : do you know if logic or gates can be found with a clock/enable signal ?

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