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    1. Sorry for not getting back sooner. At this point in time I am not aware of any E/M-Android interface that would tie directly to a radio. I would think that you would need the software to be aware of the E/M to provide signaling. Aside from that you could use a similar approach that I took with the E/M-Android interface and work a VOX circuit into it to provide PTT for the radio. Im not sure when this would be needed. Do you have a kenwood radio that is already set up for E/M and you want to tie a Android to it using some App like Zello?

      1. Can I Android E/M to simulate E&M Type I/II/V interface?
        I have a ROIP gateway which has E&M 4 wire ports(RJ45). I want to use Android E/M interface to simulate radio/LMR.

        1. Yes. This is specifically what it is for. If your interface allows for type 5 then I would suggest using that. The challenge you will have is if your RoIP gateway does not have VAD/VOX there is nothing in this design to provide COR. That being said, this will allow the RoIP interface to key an android device with an app like Zello like it would a radio. IF you have to have COR for your interface you will need to add a vox circuit that is activated off the android’s speaker out and have that trigger a relay or Transistor to provide a ground for COR to the radio interface.

          1. VOX feature is available.
            Below is the RJ45 E&M(4 wire) pin details. Impedance is 600 ohm .

            1 MREF GND
            2 M Input
            3 RX+ Input
            4 TX+ Output
            5 TX- Output
            6 RX- Input
            7 E Contact closure
            8 EREF Contact closure

            I have few more queries. Could you please share your mail Id? Thanks.

          2. Hi,

            I am really bad at electronics but this seems like something i could handle! I just dont understand the +5vdc part. Does this circuit require a external 5vdc input? Or does it get that from a pun on the radio or phone? Thanks!

          3. external 5V will need to be supplied. What I liked to do was connect a powered usb hub and plug the phone into one port so it would charge and then add a USB pigtail to supply power (USB is 5V) to this circuit.

  1. Hi,
    can you explain what switch you use “audio from phone” circuit? You have RX and TX switch, but i don’t understand how this works.

    1. I can see how that could be confusing. The switch that is shown simply allows the circuit to provide audio to the E/M port. The E/M port would be set up with VAD (aka Vox) which would cause the Router to sense voice activity and key the radio. If you place the switch to receive only it will feed Zello with audio from the radio but not allow zello users to key up the radio. This would be if you wanted to monitor a radio channel with zello.

      1. It would be great if you can make a modification, ham radio to activate the zello ptt button, in the reverse it can use the vox function of ham radio

  2. Since I am sure a lot of people would want to use this Zello interface with a UV-5R or similar HT radio, could you confirm the Kenwood pin interface with the pin numbers that you have on the E/M?
    What I think it should be is the following:
    E/M 1 = MIC+
    E/M 2, 5,6 = SPK –
    E/M 3 = MIC –
    E/M 4 = SPK+

    I took the pinout diagram of the Kenwood from the miklor website: http://www.miklor.com/COM/UV_Technical.php

    Thanks a lot for your help!

    Regards from Montreal!

    1. If you are looking to key Zello on android with a Portable radio the problem you will have is that the radio does not provide COR (carrier operated Relay). This is what the E/M port provides. In order to accomplish this you could add a simple vox circuit that would trigger off of the radios speaker audio. A better way to implement a portable radio to Zello would be to use the desktop app. this provides vox functionality. I am running a setup that uses the tigertronics signalink USB and it has been working well. I would say Most Amateur radio operators would be better off with the signalink. E/M interfaces are more typical for commercial use.

      1. The goal here is to make for a very compact system so having to use a computer is not very useful.
        Since my Radio already has a VOX function, would adding a VOX circuit be overkill?

        1. Your radio can use its built in vox to key the radio side. You will still need something to key the phone side. In my schematic I use E/M signaling. This triggers the circuit to apply the resistor across the mic and ground pins on the android device. You would need something from the radio that triggers this. On repeaters you would use COR but because portables are not designed for repeater use they typically don’t provide such a signal. This is where you would want to add a vox circuit for the phone side. Another option would be to use Mumble instead of Zello. Plumble (the Android mumble client) has built in VOX. Zello leaves this function out of its android clients. So in summary, the radio VOX works to key up the radio and you would need to add VOX the other direction to key up the Android App.

  3. I did some more research and I am thinking that I would have to set the E lead to ground when the radio is transmitting for your circuit to know when to trigger the ptt on the android. Right?

    1. Yes the Vox would be replacing the E/M signaling and yes the circuit is looking for a ground for its signal. If you get it working let me know how it works. I would love to hear about your project. Good luck.

  4. How do I modify this circuit to use it without a router and when on my smartphone zello receives the audio from the walkie or handy, a circuit closes or activates the ptt button that is in the wired headphones and thus create a vox control. I am a ham radio operator and I want to make a gateway to replace the laptop with an android smartphone. but without a router. please tell me how I can modify that circuit to achieve it. On the internet they have manufactured these gateways, but their manufacturers refuse to share the circuit. please help me.

  5. So I am able to get Zello to transmit on a HT with your interface. I set my HT to VOX level 10 and it picks up the audio from the android/zello quite well.
    My problem is that when I transmit by radio to the HT attached to the circuit, the android/zello does not key up. I have the Zello app push-to-talk button set to the play/pause button as if I were using a 3 button headset. I set the VR2 trimpot to 135 ohms.
    Not sure why it does not ptt my phone….

  6. Hello, I know absolutely nothing about this, but I use zello with friends on my Nexus 6p Android phone, and I have a Motorola rdu2080d radio that I never use anymore. It would be interesting to connect it to my phone for zello, and practical at times when I’d like to protect my phone but wouldn’t worry about damaging the radio. Is there a place to buy the hardware that would make this possible, with a very portable setup as mentioned by another user, so that I can use my phone data with my radio?

    1. I’m not too sure about your application. If you would just like to keep your phone in a backpack or pocket but still use Zello and are in close proximity then maybe a Bluetooth mic would be a good option. If you are looking to add a RF link to Zello then that would mean an interface similar to what I have only you would need to include a VOX circuit. This is what most people are looking for when they come to my site. If you are looking to tinker around and don’t mind using a PC, then I would suggest this https://www.youtube.com/watch?v=LXvhvV57UtM which is about as cheap and simple as you can get for interfacing with a radio from Zello.

    1. Joel, Sadly my priorities have prevented working on this project. I will see about trying to make a adaptation and post a report. There have been some issues with this design due to the fact that due to different manufacturers and different version of android, Phones handle the Contact closures a little different. I am thinking that a Bluetooth interface may be a better choice. Any development would probably be towards the Bluetooth option as many new phones don’t even have a 3.5mm jack.

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