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Keying a relay with a 4 or 5 pin mic ?

D

dss56

Active Member
Sep 27, 2010
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Anyone out there ever try to key a 12v or 5 volt relay with a cobra 4 or 5 pin mic external to the radio.

Like doing a project that needs a relay to key it up when the mic is keyed. I have the circuit of a 1 second pulse to key the relay and shut back off in 1 second.

Problem is on the cobra 4 pin mics on pin 3 there is 8 volts and when the mic is keyed the voltage disappears. No Voltage and comes back when mic is released.

I need the opposite 8 volts when the mic is keyed and pulsed for the 1 second and shut off.

Like i mentioned i have the 1 second circuit a transistor capacitor resistor and relay works great with external power.

When I try on a 4 pin cobra mic like I mentioned the voltage problem needing the volts when radio is keyen and not in the receive mode.

thanks for any suggestions/help
 

Does this have to be external to the radio?

If you tap into the radio's internal transmit-only voltage there is a limit to the current you can draw. Would be the simplest approach.

If it has to be external to the radio, you need a voltage source to switch on while keyed.

The mike socket will give you only the opposite of what you want. To get an "active high" voltage when you key can't be obtained from the mike jack alone.

I'm not getting a very complete picture here.

73
 
DSS: I am with NOMAD...Are you wishing to use a "Latching" Relay?
This relay requires power to open and power to close?
I guess both of us are wondering the application for this device.
All the Best
Gary
 
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Im building a project of an audio board and it needs a fast relay to be on and off like 1 second to trip the module. Like I said I have the timer circuit of 1 second and all works great with external voltage of 5-12 volts. So if i hit the timer circuit with the say 8 volts external the relay will pulse for 1 second setting off the audio module works every time.
This project will be built into a small project box and have mic in and mic out to radio.

So I was asking any way to trip the circuit to set the relay off using the mic on the radio chassis. Need 5-12 volts and as I mentioned when the radio is not keyed there is 8 volts on pin 3 and goes away when radio is keyed. the opposite of what I need.

Well Ill keep trying to get this to work some how external.

thanks
 
338_MtRushmore said:
Could just swap to a 6 pin to pull power out? I still can't think of a reason to have a relay in a mic though.
Click to expand...


The relay will not be in a mic it will be external in a project box and have an audio module that needs a relay to have it set for key up instead of doing it manual.
 
Can you pull power from someplace other than the mic jack, and use the power from the mic to flip the power? I assume you are trying to accomplish this without any modification to the radio?
 
BJ radionut said:
DSS: I am with NOMAD...Are you wishing to use a "Latching" Relay?
This relay requires power to open and power to close?
I guess both of us are wondering the application for this device.
All the Best
Gary
Click to expand...
No latching relay just need the relay to trip for 1 second. I already have it working with external power works great just need to get it to work with external to the radio project will be built in to a small project box with mic in and mic out to radio and the audio board and relay will be in the box
 
Correct no mods to the radio.
Well the box will have 12 volt going to it but still need something from the 4 pin mic connector to set the rely off for 1 second.

The Module inside the box just needs a negative pulse to set the module working. So I have one pole on the relay to control that when the relay is activated for a split second to see ground for a second.

Again got this all working with external power just need a way to get the mic to trip the relay, I'll figure something out to work.

Also this is for a 4 pin cobra and a 5 pin cobra and other radios that use the cobras mic wiring.
 
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I must be missing something. What you described could easily be achieved with a simple relay. Key mic = no power to relay = relay closed = triggered.. Unkey mic = power to relay = relay open = trigger off.
 
I need the mic to key the relay closed for a split second, then relay shuts off but keep the mic still keyed. The split second will close the relay and will send a short using 1 pole when keyed to 2 wires on the module to make it work. The module needs a split second to short 2 wires but also the mic is still keyed to send the audio to pin 2 on the 4 pin mic
 
Ah, relays come in normally closed and normally open.

You have two choices that I see.

1) Tap into the radio's internal switching. We sell a board with a relay for keying your external ham linear. A footswitch eliminator, so to speak.

The radio's internal transmit voltage feeds through a resistor into the base of a NPN transistor. The emitter is grounded, and the collector goes to one side of the relay's coil. The other side of the coil goes to the radio's main 13.8-Volt power. The transistor draws only a tiny added current from the radio's internal transmit voltage. The full current of the relay coil would probably overload it.

2) You could put the relay's coil power source in an external box, or use a wall wart. A PNP transistor gets its collector connected to ground. The emitter goes to one side of the relay coil. The other side of the relay coil goes to the power source. The transistor's base lead goes to the transmit wire in the mike plug. When the mike grounds the transmit wire, it grounds the base of the transistor, turning on the relay coil.

This method raises the possibility of feeding excess voltage into the radio's keying circuit. Some radios won't care. Other radios may blow up, damaging the computer that runs the channel selector and display. Any radio that has a 2950 inside it would be one example of this hazard.

Some radios will tolerate inserting a diode like a 1N4148 inside the radio between the radio's keying input and that pin of the mike plug. This will isolate the radio's transmit switching circuit from an external relay circuit.

Whichever way you go there needs to be a transistor in between a relay coil and the transmit pin of the mike socket. The full current of the relay coil probably shouldn't be switched directly by the mike.

Never mind the reasons. Poofing the radio becomes a risk for any radio with a relay coil connected directly to transmit pin of the mike socket.

73
 
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You used to be able to buy a high-sensitivity relay called a 'reed relay'. Sure can't get them at RatShack any more.

A magnetic reed switch, sealed inside glass gets put at the core of a wire coil. The magnetic field needed to activate the reed is pretty weak, so the current it will draw tends to be a lot less than a conventional relay. If you found one of these with a coil resistance of 600 ohms or more you could probably just power it from the radio's internal transmit voltage without disrupting it.

Would be massively simpler.

73
 
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