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ThomasScherrer

Audio track as modem data NMEA

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(1) Depends on the GPS module. Those with the MTK chipset can be accessed via a PC and the power-on defaults can be changed using the minigps PC software app. Other chipsets may require that the host controller configure the GPS's parameters at boot time. The GPS's data sheet and app guide will tell you everything you need.

(2) You will need a decent audio frequency generator that has very flat response to about 50Khz. Feed this into the transmitter's line level audio input at about 500mV to 1V and find the min/max freq's -3dB points using the oscope (connected to the A/V receiver's audio channel). It is best to perform this test using both sine and square waves to ensure that both have similar results.

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(1) Depends on the GPS module. Those with the MTK chipset can be accessed via a PC and the power-on defaults can be changed using the minigps PC software app. Other chipsets may require that the host controller configure the GPS's parameters at boot time. The GPS's data sheet and app guide will tell you everything you need.

(2) You will need a decent audio frequency generator that has very flat response to about 50Khz. Feed this into the transmitter's line level audio input at about 500mV to 1V and find the min/max freq's -3dB points using the oscope (connected to the A/V receiver's audio channel). It is best to perform this test using both sine and square waves to ensure that both have similar results.

Thanks Mr RC-Cam. I don't think I will be able to come up with the equipment to measure the audio bandwidth. I was recommended to use airwave modules as they seem to have good audio. right now all I have is the typical 900mhz range video Tx/Rx, not sure who makes them or if they are junk for this application. I am looking for some new 2.4 ghz equipment, so maybe i'll look for airwave, though the higher power stuff is all lawmate that I can find.

Could you recommend a GPS module that might be set-up properly off-the-shelf to function with these modems? If not set-up already, do you know of a specific one that is reconfigurable? I'll go to sparkfun and start reading datasheets, but I thought I would ask.

Thanks!

David

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From what I have seen, all the popular modern GPS modules are re-configurable to some extent. But if you want one that can be permanently reconfigured with special power-up defaults then the latest MTK chips set based modules do that (as well as others). The common OEM style module choices that tend to be used in our applications are the MTK based FV-M8, LS20031, LS30033. These are all small and affordable.

You can have your host soft configure them or you can use MTK's miniGPS PC app to reprogram the defaults. Keep in mind that the MTK chipset only allows 7-8 programming attempts. So, if you buy a used one be sure to ask how many programming counts are remaining.

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Advice Needed

Thanks to Thomas for sharing the FSK Modem which I intend to interface with the antenna tracker I’m building. I only intend to send Lat Lon & Height over the audio after parsing with the on board pic.

The advice I request regards the fuses of the ATTiny2313.

On the schematic (Post #17) it mentions CKDIV8 = 0 and in post #35 it states 8MHz Internal Clock, No DIV8, BOR 1.8v. What I need to know is which is correct as when you receive the chip it is set to CKDIV8 = 0 which is 1MHz (reverse logic ON = 0 OFF = 1) also why is BOR set to 1.8v as at this voltage 8MHz would be very unstable if even possible?

This information would be much appreciated as I see that this is not a straight forward make and use project and would like to know that the chip is programmed correctly before testing. I hope the above makes sense as I am an Amtel virgin.

Thanks Geoff.

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Is this project still alive ?

the dzl.dk website is down/unreachable.....

i'm looking for a "cheap/diy" way to send GPS coord through audio downlink in order to control an antenna tracking device (scc32 stuff connected to pc) and by reading this topic, i think the dzl modem could be a great solution

thanks

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thanks !

I have been trying to chase down information on using the audio channel to downlink telemetry for several days. Every seemingly hopeful path I've followed has led to a deadend. If you succeed in finding anything, PLEASE post a link here.

- Don

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Yep, i've build something, but i've restarted all from scratch 'cause noone agreed to release modem source code or correctly explain the stuff.

I'm currently at Madagscar (holidays :3 ) so i don't have file/doc/pics here, but i'll post all when i come back. I've planned to release all code/schematics for a "less-than 15$" antenna tracker

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Yep, i've build something, but i've restarted all from scratch 'cause noone agreed to release modem source code or correctly explain the stuff.

I'm currently at Madagscar (holidays :3 ) so i don't have file/doc/pics here, but i'll post all when i come back. I've planned to release all code/schematics for a "less-than 15$" antenna tracker

Penpen,

I can help. What MPU are you planning to use?

- Don

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It's already working. i have two version, one with an attiny2313 using bfsk and one with atmega8 using a kind of quartet encoding like qfsk and buffering for gps working at specific speed wiyh gps. demofulation is performed by a computer through sound card, but an an attiny could do the job.

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It's already working. i have two version, one with an attiny2313 using bfsk and one with atmega8 using a kind of quartet encoding like qfsk and buffering for gps working at specific speed wiyh gps. demofulation is performed by a computer through sound card, but an an attiny could do the job.

Great. Can't wait to see it.

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Still haven't the time to write a real post but i've put an archive here with some sources and short explaination http://www.modelisme.com/forum/aero-vol-en-immersion/167426-modem-audio-pour-telemetrie-et-antenna-tracking-gps.html sorry for waiting....

Unfortunately, you have to register at the site to be allowed to download and my French isn't good enough for me to muddle through it.

- Don

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