HT750 Multi Connector

[w8vqt]

I have a "government" job I'm working on for a freind of mine. He has some miltary surplus equipment, headphones, PTT switches and he would like to see if they can be used for this radio. My initial answer was, I think it might, but it depends on a few things. I had "assumed" that at least grounding one of the pins on the multi-connector would at least bring the unit in Tx mode. After checking the wiring diagram, I don't really see a PTT line that switches? I'm wondering if anyone would have any ideas as to how to connect externally to the PTT and rx audio lines for the Moto HT750? Please help. Thanks

 

[DPapay]

HT750/1250/1550/PRO5150/7150/9150/GP320/340/360/380/ GP318/338/GP640/680/1280/CDM750/CDM1250/CDM1550,etc.

Batlabs

 

[w8vqt]

Hello and thanks for the reply. I've actually been to this site and found the diagrams. It looks like the test set puts a ground on pin 5 of the multi connector and that brings the tx up. My problem that doesn't appear to work. I have an external mic and when I use it alone, the PTT switch on it, keys the transmitter. When I try to ground the pin 5 by itself, nothing seems to happen? I was thinking there must be something else going on other than jsut grounding pin 5?

 

[wa8pyr]

Hello and thanks for the reply. I've actually been to this site and found the diagrams. It looks like the test set puts a ground on pin 5 of the multi connector and that brings the tx up. My problem that doesn't appear to work. I have an external mic and when I use it alone, the PTT switch on it, keys the transmitter. When I try to ground the pin 5 by itself, nothing seems to happen? I was thinking there must be something else going on other than jsut grounding pin 5?

If you have RSS, read the radio and see if Pin 5 has selectable options. On that pinout it's labeled OPT SEL 2 which on other radios I've worked on indicates a pin whose function can be defined in software. If that's the case here it's possible that Pin 5 on your radio has been defined to do something else.

However, since a speaker mike works when you hook it up, that's probably not it. And now that I think about it, some speaker mikes do have a resistor to ground that has to be there for PTT to work. Try grounding through a 2.2k resistor and see what happens.

 

[w8vqt]

I don't have any way to read the radio right now. A little more background on this unit is my bosses, brother's, who is deputy sherrif. He had this stuff and my boss thought I might be able to come up with something for them to use it pretty easily. I don't really have the programming attachements or cables, etc. but I do know what you're talking about. I guess the external mic itself "must" be doing something else other than just grounding that pin to bring it into TX? I don't know if the mic is actually talking with some serial data to the radio and that's how it actually "keys" the Tx or not, but it would seem that something like that is going on? I just thought there would be an easier way to get this to work? I do appreciate any ideas you may have though...

 

[w8vqt]

I'll try the resistor trick and see if that works. I will probably have to wait till tomorrow, so I can bring some in from home. (I have more "stuff" like this at home than I do at work?...ha ha)...I'll ty that and let you know...I really appreciate your help with this thing though...
Tx

 

[w8vqt]

Well, I was able to find a resistor around here. However, that didn't do the job either? this thing is really getting to me now...ha ha

 

[bezking]

You can't modify the connector pins via CPS.

 

[w8vqt]

Can you tell me what that means? I don't work much with these radios and I'm a little lacking on the lingo. Does that mean that what I want to do cannot be done?

 

[bezking]

I was responding to WA8PYR who stated that Pin 5 may be modifiable in the CPS (the software used to program these radios). It is in fact not possible to reassign Pin 5 to do something else...

 

[w8vqt]

Ok, I understand. Would you know what actually brings the unit into Tx then, like I am wanting to do? I see where they make small headsets for this unit that look like they have nothing more than an inline PTT switch and an earphone...that's why I thought this shouldn't be all that big a deal? But for some reason, it appears to be?

 

[w8vqt]

I am still seriously looking for some help? Anyone have any ideas?

 

[bezking]

When I get home tonight I will look at some of my Pro series accessories and see what I can do for you...

 

[w8vqt]

Thanks, I would really appreciate it. I just can't understand why it's not more straight forward, I guess...

 

[w8vqt]

Hello, I'm still trying to figure out this connection problem???....

 

[bezking]

OK. PTT audio seems to go with both pin 5 and pin 4. Rx audio is on pins 1,2,6, and 7.

HTH

 

[w8vqt]

Ok, now how about the pins to that are used for PTT?

 

[bezking]

It's either 5 or 4. I'm willing to bet that it is somehow both of them.

 

[w8vqt]

Well, I've seen on batlabs a drawing of a mic circuit that has a PTT switch on it and a 4uf cap around the switch. I assume it's for the Jedi version? However, it has the PTT switch going from the "tip" in series with the speaker going to the "sleeve". Then the mic element taps the "sleeve" also and goes to the "ring". (meaning the standard tip, ring, sleeve connector). The trouble is that neither one of these really tell me what I want to know, which is "what pins has the PTT switch, what pins has the Mic audio, and what pins has the Rx audio?
By the way, I have tried pin 4 and 5 together to gnd, and pin 4 or 5 by themselves to gnd, (I also tried through a resistor as well, but it "still" does not "key" the TX ????

 

[kf8yk]

I have a "government" job I'm working on for a freind of mine. He has some miltary surplus equipment, headphones, PTT switches and he would like to see if they can be used for this radio. My initial answer was, I think it might, but it depends on a few things. I had "assumed" that at least grounding one of the pins on the multi-connector would at least bring the unit in Tx mode. After checking the wiring diagram, I don't really see a PTT line that switches? I'm wondering if anyone would have any ideas as to how to connect externally to the PTT and rx audio lines for the Moto HT750? Please help. Thanks

Try this:

Pin 1 - Speaker +

Pin 2 - Speaker -

Pin 4 - Microphone audio

Pin 5 - PTT (short 5 & 7 to transmit)

Pin 6 - External accessory port enable (short 6 & 7 to enable the side accessory port)

Pin 7 - Ground