Car audio muting circuit

[AZ_chris]

My radio has a mute wire that will activate when ground is applied to it.
I have a CDM1550, and would like it so that when I key the mic it will apply ground to this wire (i.e. shut it up so I come thru clear without background music)

Where should I start, or is there any prebuilt units available?

 

[N1GTL]

I don't think any pins on back go high or low on a PTT from the mic. You can certainly mute your am/fm radio when the CDM receives by using the COR with a relay but to mute it on a PTT, not from a rear pin.

 

[N1GTL]

After a little research, you can do this by building a type of break out box for your mic to plug into. Pin 1 is 12v which can power a small relay. You'd have to plug your mic into a box and plug the box into the mic jack on the CDM. I'd do a little research online for an existing product before trying to build one if you not proficient at electronic work.

 

[sfd119]

Breakout box would be the best bet. 12v + to a relay to activate ground. I send 12+ power to a relay to send 12- to a Vehicle Repeater to enable it.

 

[Rred]

There is a kludge you can experiement with. Your radio may draw 250mA in receive or idle mode, versus 5A or 10A in transmit mode, right? (Ballpark numbers, feel free to find the real ones.)

So...you find some glass reed switches, which are tripped open/closed by a magnetic field. Try wrapping varnished wire (from a starter or alternator rebuild shop if you've got no convenient source) around the reed switch, for the full length of the switch. And run one of your power leads through that coil of wire.

Given a little "ballpark" luck (or some serious calculating) you may find that the power your radio pulls when you transmit, is enough to close the reed contacts and that can be used to conveniently ground the mute line.

It is a cheap kludge, but when you don't have to be "exact" about power ratings and all, it can often be made to work. If you don't get enough magnetism, you can play with "more coil" or with some electronics to amplify it, your choice. And that way, there's no need to open and modify the radio.

 

[SteveC0625]

Another idea would be to find one of those old Motorola mic hang-up switch boxes. Years ago, the CTCSS (PL) was disabled by the switch in the hang-up box when you took the mic out of the holder. The switch is a simple SPST and would work perfectly for the OP's application. They come up on Ebay all the time. The only one up there right now is a little pricey at $25, but it is new out of a bulk package. One of the part numbers for this switch is TLN5181.

Motorola TLN5181A Microphone Hang Up Box w/ Switch

 

[AZ_chris]

These are all great ideas guys, thanks.
I found also that some guy makes an inline unit (Enhance Your Two-Way Radio Experience by Hearing Voice Through your Vehicle Speakers)

 

[Rred]

Gadgets like that were popular with car phones, when a "car phone" was a 3-watt dedicated cell phone for the car. Nice to know that someone still makes them.

 

[AZ_chris]

I purchased it (http://www.audiointerrupt.com/Content/TDSswitch.html) and it works great. A little pricey though for what it does at $60, but if you don't have time and/or experience like me to make one, it's a great option.

Didn't know they used them with car phones. Thanks for that tidbit @Rred.