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Thread: APRS with just an Android phone and an HT that supports VOX

  1. #1
    4x4 Ham Member Supporting Member KC7IPY's Avatar
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    Lightbulb APRS with just an Android phone and an HT that supports VOX

    Objective:
    Small and easy solution for bi-directional (TX and RX) portable APRS via RF (no Internet based APRS-IS) with as few devices as possible and a rich user interface capable of showing stations on a map.

    Solution Narrative:
    APRSDroid is an Android APRS application capable of encoding and decoding AFSK for portable APRS operations. While it supports APRS-IS (Internet based APRS), I really wanted a solution that would allow for bidirectional APRS communications in the field without being dependent on an Internet connection. I also wanted a rich user interface with offline maps and the ability to EASILY send and receive messages over APRS. The solution is really quite simple. APRSDroid can be configured to communicate via the Internet (APRS-IS), Bluetooth (requires an external TNC with bluetooth to serial connectivity), or audio input/output. In the spirit of KISS, I really didn't want to mess with any intermediate devices to facilitate keying the transmitter, so a VOX capable HT is used to key the transmitter when audio is detected. This keeps the solution very clean and simple. Two independently powered devices connected with a single passive cable.

    Required Equipment:
    • Android Device with headset jack and APRSDroid
    • HT with Speaker/MIC input and VOX
    • Custom audio cable


    My setup:
    • T-Mobile G2 Android Phone (already owned) with APRSDroid
    • Baofeng UV-3R from Amazon for $53 (small, cheap, and supports VOX)
    • Hacked up 4 conductor 3.5mm audio cable (already owned) soldered to the earpiece that was included with the UV-3R


    Details:
    The hardest part was really creating the cable. I looked up the pinout of a standard smartphone's headset jack and dissembled the earphone / mic / ptt headset that came with the UV-3R. Then I simply connected the speaker out of the UV-3R to the MIC in of my phone and the MIC in of the UV-3R to the left channel speaker out of my android phone. I then configured the "connection protocol" in APRSDroid for "AFSK via Speaker/MIC" and pressed "Start Tracking", tuned the UV-3R to 144.390 Mhz Simplex, connected the audio cable, and set the UV-3R VOX level to "7". Voila! I instantly started seeing APRS message pop up on my Android phone and beaconed out my SSID and location everytime I hit the "single shot" button (as I wasn't moving and have SmartBeaconing enabled).

    Considerations:
    • I tested everything BEFORE soldering and heat shrinking anything.
    • Any notification sounds on your Android device will cause the UV-3R to key, so set the phone to silent mode before connecting
    • There seems to be a 3 second TX hang time after my beacon is sent, probably related to the VOX setup of the UV-3R. I haven't figured out anyway to solve this.
    • Sending headphone level audio signals into a microphone input probably isn't ideal, but hey, it works!
    • I used the UV-3R specifically because it is FCC Type accepted and has a standard SMA connector with single 3.5mm 4-pin Speaker/Mic connector. Other similar radios don't meet all of these criteria.


    References:



    APRSDroid.jpg

  2. #2
    4x4 Ham Member KJ6EUO's Avatar
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    Thanks for putting this together. I have been wanting to do this with an old droid I have. It is running aprs droid already so I'm good there. Once I get my HF rig running digital this will be the next project. I'll post up here with how it works. I want to put this in the wife's car. I'm planing a nuvi 450 tied to my 50w for the jeep.

  3. #3
    4x4 Ham Member Supporting Member N7IYT's Avatar
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    Thanks for the write-up Lyle. That is an interesting project.
    Offroad and on the air.

  4. #4
    4x4 Ham Member Supporting Member KF7ORO's Avatar
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    Very cool. I need to make up a cable for my HT. It would be nice if you could set up APRSDroid to put out a PTT signal on the right speaker channel. You'd still need to step up the voltage I guess but it would be great for use with rigs that don't have VOX (like my mobile).
    Brian - KF7ORO

  5. #5
    4x4 Ham Member Supporting Member KC7IPY's Avatar
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    Quote Originally Posted by KF7ORO View Post
    Very cool. I need to make up a cable for my HT. It would be nice if you could set up APRSDroid to put out a PTT signal on the right speaker channel. You'd still need to step up the voltage I guess but it would be great for use with rigs that don't have VOX (like my mobile).
    I wonder what could be done with this: http://www.seeedstudio.com/depot/hij...html?cPath=174

    hijackwb5.jpg

    http://web.eecs.umich.edu/~prabal/projects/hijack/

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    Having a heck of a time with the tiny wires and plastic impregnation they did to each lead. Using a couple old Blackberry headsets to get the 4pin connector for the phone side, and an old plantronics headset for the 2.5mm jack on it. Going into a Yaesu CT-91 adapter into a VX-7R.

    I may break down and swing by Radio Shack to see if they have usable 4-pin 3.5mm jacks that I can just wire up cleanly with new wire as well depending on how this goes...

  7. #7
    4x4 Ham Member Supporting Member KD7WCD's Avatar
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    That is awesome! I have been looking at doing this for some time to update my APRS rig. I have been running mine on an old StreetPilot III that is getting long in the tooth that is hooked into a Kenwood TH-D7. It works great and is also a KISS type of a set up.

    Are you able to use this with Google Maps? If so can you save maps for ?off line? use. I just upgraded to a Droid (Finally!) and am loving it. So that may be a basic question I have not explored yet.

    The ease of the Droid interface looks like it would be great and Google Maps are awesome. I?ll keep an eye out for you on APRS.

    Thanks for the write up.

  8. #8
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    Quote Originally Posted by KC7IPY
    Details:
    The hardest part was really creating the cable. I looked up the pinout of a standard smartphone's headset jack and dissembled the earphone / mic / ptt headset that came with the UV-3R. Then I simply connected the speaker out of the UV-3R to the MIC in of my phone and the MIC in of the UV-3R to the left channel speaker out of my android phone.
    Can you post the details of connecting on the Baofeng end?

    I haven't been able to find a pinout diagram for the Baofeng connector, and would like to use connectors I have on hand and keep my earpiece.

    I also hope to add a couple of simple "L" pads to reduce the audio level in each direction. Have you had any issues with over-driving the audio?

    Thanks,
    Dave, W6DPS

  9. #9
    4x4 Ham Member N8KVB's Avatar
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    If your having trouble, why not use something like this

    http://www.parts-express.com/pe/show...number=090-505

    And then a standard 3.5mm male to 3.5mm male cable.

  10. #10
    4x4 Ham Member N8KVB's Avatar
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    Nevermind, I found a premade cable for those interested.

    Steren Electronics 252-684

  11. #11
    4x4 Ham Member KJ6EUO's Avatar
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    Quote Originally Posted by N8KVB View Post
    Nevermind, I found a premade cable for those interested.

    Steren Electronics 252-684
    Link added... http://www.sterenusa.com/audio-patch-cord-8
    So the Baofeng just runs a 2.5mm Cable? Its not one of these multi-pronged deals like say the Kenwoods?KenwoodMic.PNG or are you just using on the of the two connectors?... Don't you need to radio output to go to the the phone as well to receive messages?

  12. #12
    4x4 Ham Member N8KVB's Avatar
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    Quote Originally Posted by KJ6EUO View Post
    Link added... http://www.sterenusa.com/audio-patch-cord-8
    So the Baofeng just runs a 2.5mm Cable? Its not one of these multi-pronged deals like say the Kenwoods?KenwoodMic.PNG or are you just using on the of the two connectors?... Don't you need to radio output to go to the the phone as well to receive messages?
    Maybe it's more complicated than i initially though, i thought it was just an adaption of a 2.5 to 3.5mm jack.

  13. #13
    4x4 Ham Member KJ6EUO's Avatar
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    Well don't take my word on it. I'm basically asking here, but I thought it was a bit more complicated than just getting to a 2.5mm... Waiting on KC7IPY to shed some light

  14. #14
    Administrator Supporting Member K7VZ's Avatar
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    I think it's 3 wires. Output from radio to phone, input from phone to radio, and a common ground. I believe he adjusted volume via the phone.
    Virgil - K7VZ
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  15. #15
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    Quote Originally Posted by K7VZ View Post
    I think it's 3 wires. Output from radio to phone, input from phone to radio, and a common ground. I believe he adjusted volume via the phone.
    It uses three contacts from a four contact, 3.5mm, plug. The plug is the same a the one used by older Yaesu HTs. I was able to find the pinout for the Baofeng on the Yahoo Group for the radio, and chopped up a Yaesu cloning cable and re-arranged.

    I did put 500 ohm resistors in the audio lines to reduce the drive into the mic inputs a bit.

    On the Baofeng end, the common is the contact closest to the plug body, the speaker out is the tip, and the mic input is the ring closer to the tip.

    On the Droid end, the mic is the contact closest to the plug body, the common is the ring closer to the body, and the speaker is the tip.

    If you count contacts starting at the tip as one:

    Baofeng, 1=speaker out; 2=mic in; 3=Push-to-talk (not used in this application), and 4=common
    Droid, 1=Left speaker out, 2=right speaker out (not used in this application), 3=common, and 4=Mic input

    You adjust the volume of the HT, and the app adjusts the volume of the phone.

    Hopefuly some of that is clear. Here is an attempt at a drawing:
    Baofeng to Droid Adapter Cable.jpg

    I have mine transmitting and I can hear it on another tranciever. I cantt normally get into any digis or gateways from my house, but tomorrow while out and about I will try to send some shots and see if I show up on APRS.FI. I will be using W6DPS-7 for this set-up.

    Dave

  16. #16
    4x4 Ham Member Supporting Member KC7IPY's Avatar
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    KD7WCD: APRSdroid does in fact support "offline maps" and the application uses Google Maps as the map source. An even better mobile APRS solution is to use a small TNC that is directly connected to the radio and a bluetooth module to connect to the phone. This gets rid of the need for VOX (and the challenges that come along with it). There is even an option bluetooth adapter available for the TinyTrak4: http://www.byonics.com/tinytrak4/

  17. #17
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    Cool

    Quote Originally Posted by W6DPS View Post
    ...I have mine transmitting and I can hear it on another tranciever... I will be using W6DPS-7 for this set-up...
    120708 APRS.jpg

    It seems to basically work for transmitting and receiving.

    The issue I have to work through now is keeping RF from getting back into the phone. When it transmits the MP3 app opens about a third of the time.
    Until I solve this I will only use it to "Single Shot" while stopped.

    I want to rework the cable anyway, since it is only about a foot long currently. I had planned to keep it short for actual pedestrian use. I now plan to add some length, maybe a way to hook to a computer sound card jacks for packet, and it looks like I need to add some ferrite chokes.

    It might help with an external antenna, also. I have been playing around with just the rubber duck that came with the HT.

    Dave, W6DPS

  18. #18
    4x4 Ham Member Supporting Member KD7WCD's Avatar
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    Oooh. I may have to look into the Bluetooth adapter. I already have a TT4 that I have build but not set up into a system yet. (That is it's own sad story.) It would be great to use that as well. I think my end goal is to loose my current GPS. The option of using a small Android table is the direction I am thinking of. Seems to make sense in the budget compared to going in the direction of an AvMap GPS. Then the tablet would also be available to other task like logging contact and all those other fun apps out there for Hams.

    Thanks for the info.

  19. #19
    4x4 Ham Member N8KVB's Avatar
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    Is there a technical name for this connector? I want to make up a cord to try this with my Puxing, but want to do a search to see if anything is commercially available first.
    Attached Images Attached Images

  20. #20
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    Does it work if you turn off the cellular features on the phone? That could be a good use for an older phone.

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