CDM1250 Changing mic from front to rear

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Jtsou
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CDM1250 Changing mic from front to rear

Post by Jtsou »

Is it possible on a CDM1250 to move the mic to from the front to the rear using the rear accessory connector?

Basically I'm trying to move the mic to the rear connector to get it out of the way.

I've got the ground, PTT, and Mic audio lines on the rear, however there's a +8v on the front that does not seem to be on the back.

Thanks!
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jackhackett
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Re: CDM1250 Changing mic from front to rear

Post by jackhackett »

Not sure what +8v you're talking about, there's no +8v on the mic connector.

As far as I remember it, you'll need the following connections:

Pin 2 - External mic audio
Pin 3 - PTT
Pin 7 - Ground

If you want the hang up function you have to use one of the I/O pins and set it up in programming, if I remember correctly I usually used pin 14 for that. You'll also have to put a dummy plug with a jumper in the front mic jack or the radio will think it's off hook all the time. If you don't want hang up you can disable 'off hook disables pl' and/or 'off hook disables scan' in the programming.
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SteveC0625
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What radios do you own?: CDM's, CP's, CM's, and more

Re: CDM1250 Changing mic from front to rear

Post by SteveC0625 »

EBay seller mre1032 has a cable specific for this purpose. It can also be had with external speaker leads and an ignition sense lead. His work is the best and he’s recommended by many folks.
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kcbooboo
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Re: CDM1250 Changing mic from front to rear

Post by kcbooboo »

The MIC Audio on the front panel has about 9VDC on it to power the preamp built into almost all Motorola mikes. Since one doesn't normally plug a mike into the Acc Conn, they don't provide power on the TX Audio input for that. Also the front panel MIC Audio input is pre-emphasized; the Acc Conn TX Audio input can be flat or pre-emphasized depending on a setting in CPS. There are probably other differences in audio response since the Acc Conn TX Audio input is good down to almost DC so you can feed in PL/DPL signals, which won't pass through the front panel MIC Audio input.
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jackhackett
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Re: CDM1250 Changing mic from front to rear

Post by jackhackett »

[quote=kcbooboo post_id=505268 time=1603561815 user_id=1485]
Since one doesn't normally plug a mike into the Acc Conn, they don't provide power on the TX Audio input for that
[/quote]

I'm pretty sure they do have the bias on the Acc connector.
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SteveC0625
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What radios do you own?: CDM's, CP's, CM's, and more

Re: CDM1250 Changing mic from front to rear

Post by SteveC0625 »

jackhackett wrote:
Tue Oct 20, 2020 6:32 pm
Not sure what +8v you're talking about, there's no +8v on the mic connector.

As far as I remember it, you'll need the following connections:

Pin 2 - External mic audio
Pin 3 - PTT
Pin 7 - Ground

If you want the hang up function you have to use one of the I/O pins and set it up in programming, if I remember correctly I usually used pin 14 for that. You'll also have to put a dummy plug with a jumper in the front mic jack or the radio will think it's off hook all the time. If you don't want hang up you can disable 'off hook disables pl' and/or 'off hook disables scan' in the programming.
Jack,

You posted some of this info SIXTEEN YEARS ago. I added some comments and created an info sheet that pretty much answers any questions about this whole thing. BTW, I thank you profusely for this help and much other guidance way back when. Here's my sheet:

CDM Mobiles: Microphone via the Accessory Connector
Post by jackhackett » Mon Mar 15, 2004 11:58 am
Hook everything to the acc. conn:
Mic 3 – HOOK – ACC 6 (Assign in CPS)
Mic 4 - GND - ACC 7
Mic 5 – MIC HI - ACC 2
Mic 6 - PTT - ACC 3 (Assign in CPS)
External Loudspeaker - ACC 1 and 16
Ignition Sense – ACC 10
In the CPS:
Radio Configuration -> Accessory Pins tab -> Accessory Package: Default which makes pin 3 External Mic PTT (Input), Active Level = Low, and Debounce Enable checked.
Radio Configuration -> Accessory Pins tab -> Set pin 6 as Mic Off Hook (Input), Active Level = Low, and Debounce Enable checked.
Then Radio Configuration -> Accessory Configuration tab -> set Ext. PTT Audio Source: Ext Mic Audio
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