PTT weirdness (and Mobilinkd TNC2)

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F1RMB
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Re: PTT weirdness (and Mobilinkd TNC2)

Post by F1RMB » Wed Mar 25, 2020 6:55 am

Hi,
KC7RBW wrote:
Wed Mar 25, 2020 6:49 am
Thanks for the help so far, Jens!

Here's what I learned by poking around with a cheap multimeter:
This first part is interesting, but I don't think this is the problem...
  • Speaker mic
    • PTT not pressed
      • 2.5mm sleeve (GND) and 2.5mm tip (Speaker) are connected with a slight resistance
      • Nothing else is connected
    • PTT pressed
      • 3.5mm sleeve (PTT) and 2.5mm sleeve (GND) are connected with almost no resistance
      • 2.5mm sleeve (GND) and 2.5mm tip (Speaker) are still connected with a slight resistance
      • 3.5mm sleeve (PTT) and 2.5mm tip (Speaker) are of course also connected the same
  • TNC2
    • Not transmitting (PTT not pressed)
      • Nothing is connected
    • Transmitting (PTT pressed)
      • 3.5mm sleeve (PTT) and 2.5mm sleeve (GND) are connected with a slight resistance
      • Nothing else is connected
Here's where I think the problem really is...
  • GD-77
    • With generic cables
      • Shorting 3.5mm sleeve (PTT) and 2.5mm sleeve (GND) triggers PTT
      • 3.22V measured between these two points
    • With TNC2 TRRS cable
      • Shorting TNC2 TRRS sleeve and Ring 1 does not trigger PTT
      • Around 0.35V measured between these two points
So I think what's happening is that the TNC2 cable is kicking the radio into USB mode, which lowers the voltage the radio puts between PTT and ground for that detection (presumably to avoid triggering PTT while connected to USB).

I don't know how the radio decides this. I can't figure how it's possible since in both cases, as far as I know, the wires are open-ended until they are connected to something. But I tested it many times while trying to figure out what was going on and the results above are completely consistent.

Is there maybe a capacitance being measured to detect if long wires are present?
Just FYI, there is a 10k pull-up resistor connected to +3V3 on the PTT signal in the GD-77. I didn't look at your TNC schematics yet.


Cheers.
73 de Daniel.

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F1RMB
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Re: PTT weirdness (and Mobilinkd TNC2)

Post by F1RMB » Wed Mar 25, 2020 7:15 am

F1RMB wrote:
Wed Mar 25, 2020 6:55 am
Hi,
KC7RBW wrote:
Wed Mar 25, 2020 6:49 am
Thanks for the help so far, Jens!

Here's what I learned by poking around with a cheap multimeter:
This first part is interesting, but I don't think this is the problem...
  • Speaker mic
    • PTT not pressed
      • 2.5mm sleeve (GND) and 2.5mm tip (Speaker) are connected with a slight resistance
      • Nothing else is connected
    • PTT pressed
      • 3.5mm sleeve (PTT) and 2.5mm sleeve (GND) are connected with almost no resistance
      • 2.5mm sleeve (GND) and 2.5mm tip (Speaker) are still connected with a slight resistance
      • 3.5mm sleeve (PTT) and 2.5mm tip (Speaker) are of course also connected the same
  • TNC2
    • Not transmitting (PTT not pressed)
      • Nothing is connected
    • Transmitting (PTT pressed)
      • 3.5mm sleeve (PTT) and 2.5mm sleeve (GND) are connected with a slight resistance
      • Nothing else is connected
Here's where I think the problem really is...
  • GD-77
    • With generic cables
      • Shorting 3.5mm sleeve (PTT) and 2.5mm sleeve (GND) triggers PTT
      • 3.22V measured between these two points
    • With TNC2 TRRS cable
      • Shorting TNC2 TRRS sleeve and Ring 1 does not trigger PTT
      • Around 0.35V measured between these two points
So I think what's happening is that the TNC2 cable is kicking the radio into USB mode, which lowers the voltage the radio puts between PTT and ground for that detection (presumably to avoid triggering PTT while connected to USB).

I don't know how the radio decides this. I can't figure how it's possible since in both cases, as far as I know, the wires are open-ended until they are connected to something. But I tested it many times while trying to figure out what was going on and the results above are completely consistent.

Is there maybe a capacitance being measured to detect if long wires are present?
Just FYI, there is a 10k pull-up resistor connected to +3V3 on the PTT signal in the GD-77. I didn't look at your TNC schematics yet.


Cheers.
It would be nice to measure the voltage on the SiA914DJ mosfet base when PTT is ON.
Have you probed and measured the PTT wiring on this "TNC2 TRRS" cable ?


Cheers.
---
Daniel
73 de Daniel.

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Re: PTT weirdness (and Mobilinkd TNC2)

Post by F1RMB » Wed Mar 25, 2020 7:35 am

Also, regarding turning the GD-77 into "USB" mode, unless you have some shortcuts in the cable, USB Data+ and Data- are using the jack's +5V (3.5mm tip) and PROG (2.5 ring) connections.

Just to be sure, try to insert the "Kenwood K" connector when the GD is OFF.

Cheers.
---
Daniel.
73 de Daniel.

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DG1YFX
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Re: PTT weirdness (and Mobilinkd TNC2)

Post by DG1YFX » Wed Mar 25, 2020 9:07 am

https://www.mouser.de/datasheet/2/427/s ... 764433.pdf
There may be a fault with the TNC2. Is the double MOSFET soldered in the wrong way round? To test if the TNC2 circuit works, connect a LED and 1k resistor in series to +5V on the TNC board to PTT. When TNC2 is transmitting, the LED should be on.

The 0,35 volts looks suspicious. Could be a diode which prevents the PTT to be released. So if you switch on the GD77 and then plug in the TNC2 cable, what happens? I recon it starts to transmit right away.

73s,
Jens

KC7RBW
Posts: 131
Joined: Wed Nov 20, 2019 1:23 am

Re: PTT weirdness (and Mobilinkd TNC2)

Post by KC7RBW » Fri Mar 27, 2020 4:53 pm

DG1YFX wrote:
Wed Mar 25, 2020 9:07 am
https://www.mouser.de/datasheet/2/427/s ... 764433.pdf
There may be a fault with the TNC2. Is the double MOSFET soldered in the wrong way round?
The problem exists independent of the TNC2. It's just the little cable that triggers the problem.
F1RMB wrote:
Wed Mar 25, 2020 7:35 am
Just to be sure, try to insert the "Kenwood K" connector when the GD is OFF.
DG1YFX wrote:
Wed Mar 25, 2020 9:07 am
So if you switch on the GD77 and then plug in the TNC2 cable, what happens? I recon it starts to transmit right away.
It operates the same way regardless of when the cable was plugged in.

I no longer think it has anything to do with USB, because I can use splitters to have USB and a speaker mic both plugged in at the same time, and the voltage for the PTT doesn't change.

In fact, I can make this problem go away by plugging in the cable through the splitter, as pictured here.
IMG_20200326_104043 (1).jpg
IMG_20200326_104043 (1).jpg (248.56 KiB) Viewed 78 times
I can't see any difference between the Kenwood K connectors, though I haven't pulled out my calipers yet.

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Re: PTT weirdness (and Mobilinkd TNC2)

Post by DG1YFX » Fri Mar 27, 2020 5:29 pm

It looks like there is a difference between the Kenwood and the Radioddity plug.

As I've got a Kenwood microphone, I have both plugs here.
Radioddity:
radioddity.jpg
radioddity.jpg (15.65 KiB) Viewed 75 times
Kenwood:
kenwood.jpg
kenwood.jpg (14.9 KiB) Viewed 75 times
There is a difference in the 2,5mm plug which could be the culprit.

73s,
Jens

KC7RBW
Posts: 131
Joined: Wed Nov 20, 2019 1:23 am

Re: PTT weirdness (and Mobilinkd TNC2)

Post by KC7RBW » Fri Mar 27, 2020 6:22 pm

The fellow who makes the TNC 2 suggested it could be a difference in the spacing between the two plugs causing a poor connection. I tried to measure it with my cheap calipers and the plug that's not working well has the plugs about 0.75mm closer on average than other connectors I have. Been trying to find photos of how the jacks are oriented in the GD-77 to see if this could explain it.

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