Help making a carrier operated switch

[prcguy]

I would not expect 900ma anywhere in the keying circuit. You could put the multimeter in current mode and put one lead at ground and the other on the mic pin that keys the radio. That will key the radio and tell you how much current is drawn through the mic PTT switch. Probing the same points with the multimeter in the DC volt mode will tell you if the mic PTT is pulling the key line all the way to ground or not. It may not if you measured 4 volts but any aftermarket mic will be a direct short from ground to the key line when you push the mic button.

Those are the readings I got when I would key the microphone on the uniden 510xl. I used my multimeter on the ground and the transmit terminals on the ptt switch.

 

[ThomasB3131]

Well I think I finally got the correct readings. I got 8volts at 80 to 83 ma when I probed right at the mic jack which sounds a little bit closer to normal than the first time.

I should probably figure out how many ma the squelch circuit puts out and then find a transistor with the appropriate saturation level, correct?

Thanks again for your help, I definitely couldn't gotten this far without it.

 

[prcguy]

I think the transistor switch in the link would not load down the squelch circuit but you could also search for an FET inverting switch which would have a higher impedance and less loading. When you attach the transistor switch you can take voltage readings before and after the switch is installed to see if its affecting the 8 volt unsquelched line.

Well I think I finally got the correct readings. I got 8volts at 80 to 83 ma when I probed right at the mic jack which sounds a little bit closer to normal than the first time.

I should probably figure out how many ma the squelch circuit puts out and then find a transistor with the appropriate saturation level, correct?

Thanks again for your help, I definitely couldn't gotten this far without it.

 

[ThomasB3131]

I think the transistor switch in the link would not load down the squelch circuit but you could also search for an FET inverting switch which would have a higher impedance and less loading. When you attach the transistor switch you can take voltage readings before and after the switch is installed to see if its affecting the 8 volt unsquelched line.

Ok so I have three transistors to choose from the PNP, NPN, and the FET transistors.

I think I am going to use the 2n3906 transistor, a variable resistor 10-20k as you suggested, the reed relay, and the 1n4001 diode for the voltage spikes.

I am going to try the make the transistor circuit pictured in figure 3 from the link you provided in one of your posts above.

would that be the right combination of parts for that circuit?

 

[prcguy]

I think it was figure 2 in the link that was an inverting switch, so when the radio goes from 0 to 8 Volts when it unsquelches, the transistor will pull something to ground. That something is a relay coil with one side tied to 12V and the other to the transistor so it energizes the relay coil.

Ok so I have three transistors to choose from the PNP, NPN, and the FET transistors.

I think I am going to use the 2n3906 transistor, a variable resistor 10-20k as you suggested, the reed relay, and the 1n4001 diode for the voltage spikes.

I am going to try the make the transistor circuit pictured in figure 3 from the link you provided in one of your posts above.

would that be the right combination of parts for that circuit?

 

[ThomasB3131]

So a resistor is hooked up to the 8volts off of the squelch circuit and the transistor is then hooked up to that, then another resistor is shorted to ground from the transistor, then the relay is hooked up to the transistor as well. Is that what the schematic says in figure 2? Sorry, I am not very good at reading schematics.

 

[prcguy]

R1 in Fig 2 would go to your 8 volt squelch line. The relay coil would go where it says "To Load".

So a resistor is hooked up to the 8volts off of the squelch circuit and the transistor is then hooked up to that, then another resistor is shorted to ground from the transistor, then the relay is hooked up to the transistor as well. Is that what the schematic says in figure 2? Sorry, I am not very good at reading schematics.

 

[ThomasB3131]

R1 in Fig 2 would go to your 8 volt squelch line. The relay coil would go where it says "To Load".

Alright, and R1 is connected to the collector lead on the transistor, the emitter lead would be connected to the reed relay, and the base lead would be connected to R2 which is shorted to ground correct?