Wiring a headphone jack

[Shrek]

I have an old metal detector that has speaker only for output.
It makes constant noise as there is no discrimination knob. I'd like
to wire a headphone jack so my kids can detect with it without
annoying everyone.

I purchased Radio Shack 274-248 jack, and am looking for a schematic
or instructions for how to wire it in. Obviously the speaker has 2
wires, but the jack has 3 terminals. What wires go where?

-??

 

[Don Taylor]

Shrek <Skippy> writes:

I have an old metal detector that has speaker only for output.
It makes constant noise as there is no discrimination knob. I'd like
to wire a headphone jack so my kids can detect with it without
annoying everyone.

I purchased Radio Shack 274-248 jack, and am looking for a schematic
or instructions for how to wire it in. Obviously the speaker has 2
wires, but the jack has 3 terminals. What wires go where?

Some jacks have only 2 terminals, you push the plug in and the tip
connects with one of these while further back the barrel of connets
with the other. But that doesn't switch between a speaker when the
plug isn't in and the headphones when the plug is in.

So, think of what you have as a switch. One of the terminals is
for the ground side, that is going to connect to one side of your
current speaker. Internal to the jack that is also going to
connect to one side of your headphones. Next you have the audio
that was going to your speaker, but you are going to slice that
away from the speaker and route it into the second terminal. Then
when the plug is in it will go out to the headphones. And when the
plug is out it is going to come back out the third terminal and go
back to the speaker.

Now, there is a little diagram on the back of the package. Look
for the terminal that connects to the little contact inside that
touches the barrel of your plug. That's your ground. The other
two contacts are going to be for what looks sort of like a little
switch in the diagram. When you push the plug in it pushes the
contacts and "changes the position of the switch."

You can wire this up backwards, I did the last time I was doing
this. The only bad thing would be if you shorted out the two
wires that had gone to your speaker. When you first try it do
something to make sure you should have sound and then just turn
it on for a second, and then back off. Repeat with the plug in.
If you just do this for a second you can probably tell you aren't
hearing what you should be and turn off the power before toasting
anything. Otherwise it is more likely that you will have it
backwards and won't get audio to the head phones. If you happen
to have a little ohmmeter you can try to check the connections to
see if you have low ohms where it makes sense and millions of
ohms when it should be open.

And the little plastic case that the jack is built in, it doesn't
do very well with soldering on the wires, realizing it is wrong,
unsoldering the wires, resoldering them, etc. The plastic melts
if you aren't careful. But a little caution should be enough.

See if you can compare this to what you have and how much of it
matches up.

If you still have questions then throw me mail
(address is valid)