portable headphone mixer/switcher

D

Doug Kite

Guest
I would like to combine the headphone outputs from a small fm radio, a
FRS two-way radio, and a scanner into one heaphone out. So basically,
you would hear the radio signal unless someone transmitted on the
two-radio or the scanner picked up a signal. The system must be small
and portable, preferrably powered by a 9-volt battery.

I found many examples of small portable headphone amps with an LM386. My
original idea is just to use a simple passive resistive mixer on the
inputs, run the output of that mix through an LM386 amp like so:

input1---/\/\/\-----+
|
input2---/\/\/\-----+---LM386 amp------headphones
|
input3---/\/\/\-----+

What I would *really* like to do is have it so that there is a relay or
vox-type circuit that would "prioritize" the inputs. In other words, you
would hear input3 as long as neither of the other two had signal. If
input2 activates, cut off input3 until that signal is gone. And if you
get signal from input1, cut off both 2 and 3 until it's done. This would
be better than hearing a mix of the signals. Any ideas on how to build
such a circuit?

Thanks,
Doug
 
On Fri, 19 Nov 2004 12:49:11 -0500, Doug Kite <dougkite@yahoo.com>
wrote:

I would like to combine the headphone outputs from a small fm radio, a
FRS two-way radio, and a scanner into one heaphone out. So basically,
you would hear the radio signal unless someone transmitted on the
two-radio or the scanner picked up a signal. The system must be small
and portable, preferrably powered by a 9-volt battery.

I found many examples of small portable headphone amps with an LM386. My
original idea is just to use a simple passive resistive mixer on the
inputs, run the output of that mix through an LM386 amp like so:

input1---/\/\/\-----+
|
input2---/\/\/\-----+---LM386 amp------headphones
|
input3---/\/\/\-----+

What I would *really* like to do is have it so that there is a relay or
vox-type circuit that would "prioritize" the inputs. In other words, you
would hear input3 as long as neither of the other two had signal. If
input2 activates, cut off input3 until that signal is gone. And if you
get signal from input1, cut off both 2 and 3 until it's done. This would
be better than hearing a mix of the signals. Any ideas on how to build
such a circuit?
Click to expand...
---
Check abse under the same subject heading.

--
John Fields
 
On Fri, 19 Nov 2004 12:49:11 -0500, Doug Kite wrote:

I would like to combine the headphone outputs from a small fm radio, a
FRS two-way radio, and a scanner into one heaphone out. So basically,
you would hear the radio signal unless someone transmitted on the
two-radio or the scanner picked up a signal. The system must be small
and portable, preferrably powered by a 9-volt battery.

I found many examples of small portable headphone amps with an LM386. My
original idea is just to use a simple passive resistive mixer on the
inputs, run the output of that mix through an LM386 amp like so:

input1---/\/\/\-----+
|
input2---/\/\/\-----+---LM386 amp------headphones
|
input3---/\/\/\-----+

What I would *really* like to do is have it so that there is a relay or
vox-type circuit that would "prioritize" the inputs. In other words, you
would hear input3 as long as neither of the other two had signal. If
input2 activates, cut off input3 until that signal is gone. And if you
get signal from input1, cut off both 2 and 3 until it's done. This would
be better than hearing a mix of the signals. Any ideas on how to build
such a circuit?

The logic shouldn't be hard - take what you've got there and make
Click to expand...
a truth table, then just slap a few gates together, like ands and
inverters, the first one inhibits the next, and so on.

inputs outputs
A B C Qa Qb Qc
0 0 0 0 0 0
0 0 1 0 0 1
0 1 0 0 1 0
0 1 1 0 1 0
1 0 0 1 0 0
1 0 1 1 0 0
1 1 0 1 0 0
1 1 1 1 0 0

Hey - that was easier than I thought. ;-)

And of course, they come from three little VOXes with logic outputs,
which also control analog switches.

Have Fun!
Rich
 
On Fri, 19 Nov 2004 23:34:53 GMT, Rich Grise <rich@example.net> wrote:

On Fri, 19 Nov 2004 12:49:11 -0500, Doug Kite wrote:

I would like to combine the headphone outputs from a small fm radio, a
FRS two-way radio, and a scanner into one heaphone out. So basically,
you would hear the radio signal unless someone transmitted on the
two-radio or the scanner picked up a signal. The system must be small
and portable, preferrably powered by a 9-volt battery.

I found many examples of small portable headphone amps with an LM386. My
original idea is just to use a simple passive resistive mixer on the
inputs, run the output of that mix through an LM386 amp like so:

input1---/\/\/\-----+
|
input2---/\/\/\-----+---LM386 amp------headphones
|
input3---/\/\/\-----+

What I would *really* like to do is have it so that there is a relay or
vox-type circuit that would "prioritize" the inputs. In other words, you
would hear input3 as long as neither of the other two had signal. If
input2 activates, cut off input3 until that signal is gone. And if you
get signal from input1, cut off both 2 and 3 until it's done. This would
be better than hearing a mix of the signals. Any ideas on how to build
such a circuit?

The logic shouldn't be hard - take what you've got there and make
a truth table, then just slap a few gates together, like ands and
inverters, the first one inhibits the next, and so on.

inputs outputs
A B C Qa Qb Qc
0 0 0 0 0 0
0 0 1 0 0 1
0 1 0 0 1 0
0 1 1 0 1 0
1 0 0 1 0 0
1 0 1 1 0 0
1 1 0 1 0 0
1 1 1 1 0 0

Hey - that was easier than I thought. ;-)

And of course, they come from three little VOXes with logic outputs,
which also control analog switches.
Click to expand...
---
BIG help...

--
John Fields
 
On Fri, 19 Nov 2004 18:08:26 -0600, John Fields wrote:

On Fri, 19 Nov 2004 23:34:53 GMT, Rich Grise <rich@example.net> wrote:

On Fri, 19 Nov 2004 12:49:11 -0500, Doug Kite wrote:

I would like to combine the headphone outputs from a small fm radio, a
FRS two-way radio, and a scanner into one heaphone out. So basically,
you would hear the radio signal unless someone transmitted on the
two-radio or the scanner picked up a signal. The system must be small
and portable, preferrably powered by a 9-volt battery.

I found many examples of small portable headphone amps with an LM386. My
original idea is just to use a simple passive resistive mixer on the
inputs, run the output of that mix through an LM386 amp like so:

input1---/\/\/\-----+
|
input2---/\/\/\-----+---LM386 amp------headphones
|
input3---/\/\/\-----+

What I would *really* like to do is have it so that there is a relay or
vox-type circuit that would "prioritize" the inputs. In other words, you
would hear input3 as long as neither of the other two had signal. If
input2 activates, cut off input3 until that signal is gone. And if you
get signal from input1, cut off both 2 and 3 until it's done. This would
be better than hearing a mix of the signals. Any ideas on how to build
such a circuit?

The logic shouldn't be hard - take what you've got there and make
a truth table, then just slap a few gates together, like ands and
inverters, the first one inhibits the next, and so on.

inputs outputs
A B C Qa Qb Qc
0 0 0 0 0 0
0 0 1 0 0 1
0 1 0 0 1 0
0 1 1 0 1 0
1 0 0 1 0 0
1 0 1 1 0 0
1 1 0 1 0 0
1 1 1 1 0 0

Hey - that was easier than I thought. ;-)

And of course, they come from three little VOXes with logic outputs,
which also control analog switches.

---
BIG help...
Click to expand...
Well, we don't like to do homework for people, but since it's not
exactly homework, and it's evident from the snottiness of your remark
that you're not competent to come up with the logic to implement the
truth table as shown, I'll help out:

A ----+-------------------------------Qa
|
+--|>o---+--|
| |AND --------------Qb
B -------------)--|
| |
| +--|
+--|>o------|AND ---------------Qc
C ----------------|

Cheers!
Rich
 
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