Shop our Airplanes Products Drone Products Sales
Apr 01, 2012, 12:08 PM
Registered User
Sorry for the wobbly pic of the osd in action, I was too happy that its working so my hand was a little bit shakey , this is my first pcb btw.

Got gps lock outside pretty fast (behaviour red led stopped blinking and stopped shining).

More pics arriving soon.

Btw what is the basic principle of how an audio modem works?
Sign up now
to remove ads between posts
Apr 01, 2012, 12:46 PM
Just another user
Dennis Frie's Avatar
Thanks for sharing, very nice to see you guys still build etc. My OSD have been taped inside my plane for months .

The audio-modem is AC-coupled, so in general you use the same principle as used in radio-communication. You send a sine-wave, and by changing the frequency just a little bit, you can send 1 or 0. For the audio-modem you can use a square-wave and change the frequency of a single wave to represent 1 etc.
Apr 01, 2012, 06:35 PM
Flying TRI! Thank You Alex!

Audio Modem - audio frequency range


Hi Dennis. What is the frequency range of the audio modem?
Apr 01, 2012, 06:48 PM
Just another user
Dennis Frie's Avatar
Quote:
Originally Posted by PilotGuy95 View Post
Hi Dennis. What is the frequency range of the audio modem?
The frequency range? The test-sketch linked earlier uses a PWM-output with a base-frequency around 2 khz as far as I remember. I can't remember the frequency deviation, but I increased it a bit compared to the one used by Melih/Flytron. But you can just change the frequency if you want.

What do you need it for?
Apr 01, 2012, 10:08 PM
Registered User
Dennis

Do you have a schematic for your audio modem? Or can you give a brief description of the hardware?

Thanks
Apr 02, 2012, 04:27 AM
Just another user
Dennis Frie's Avatar
Quote:
Originally Posted by pia32 View Post
Dennis

Do you have a schematic for your audio modem? Or can you give a brief description of the hardware?

Thanks
A simple AC-coupling of the PWM-output and a voltage-divider to match your audio-input should do the trick
Apr 02, 2012, 04:29 AM
Just another user
Dennis Frie's Avatar
Just a quick picture. I know the text OSD text isn't perfect, but the OSD is still taped inside the plane



- and we got a bit of snow as well.




Apr 02, 2012, 05:17 AM
Registered User
Scheme would have a full transmitter and receiver or input PC audio card
and the pc and sw arduino?
thank you very much
sorry for my English is google.
Apr 02, 2012, 05:47 AM
Just another user
Dennis Frie's Avatar
Quote:
Originally Posted by bag63 View Post
Scheme would have a full transmitter and receiver or input PC audio card
and the pc and sw arduino?
thank you very much
sorry for my English is google.
Sorry, I don't quite understand the translation.
I believe the OSD have enough cpu-time left to be used as audio-modem too.

On the ground I would use another Arduino to decode the data and perhaps also control an antenna-tracker etc.
Apr 02, 2012, 06:32 AM
Registered User
onlyifamppowered's Avatar
HI
Noobie here.
I love this project !
It's now on the top of my next build bit for expanding into more fpv.I have build several arduino Wii boards for multi's and feel up to this task.
I have read 60+ pages so far and most makes sense however I think more people could get this going with a real simple " put this wire here" type of diagram. The schamatic is easy enough to follow but I am still a little unsure as to how to wire the gps into the whole thing.
I might be a bit slow but I am sure I am not a lone of this.
This looks like a fantastic and cheap way to get into the electronic side of the hobby for the less techinically minded..
Long live open source !
Rob
Apr 02, 2012, 07:30 AM
Registered User
Best bet for you is to buy the flytron 10Hz GPS that is already on a breakoutboard...On that board you will see +,-,R and T...+ and - are for powering the unit (with 5V)...R on the GPS you have to connect to TX on arduino..and T on the GPS you have to connect to RX on arduino.
Apr 02, 2012, 07:44 AM
Registered User
Dennis I took a look at the audio-modem code...basically this is just the protocol for sending the data right, there are not yet any routines yet added to extract data from the gps right? Will you add it? so the data will go out from one of the analog pins right..I already layed out one more..
and the data would go to audio in on the vtx right?
Apr 02, 2012, 10:38 AM
Registered User
rimshotcopter's Avatar
Here is what I believe would be a good way of connected the Arduino to the Sound/audio signal of the transmitter. Substitute the speaker for the audio-in on the transmitter.

http://arduino.cc/en/Tutorial/Tone

Of course, we need to develop a scheme for sending the data. Decoding I am still working on that.
Apr 02, 2012, 10:53 AM
Just another user
Dennis Frie's Avatar
Quote:
Originally Posted by msev View Post
Best bet for you is to buy the flytron 10Hz GPS that is already on a breakoutboard...On that board you will see +,-,R and T...+ and - are for powering the unit (with 5V)...R on the GPS you have to connect to TX on arduino..and T on the GPS you have to connect to RX on arduino.
Yup - thanks for explaning

Quote:
Originally Posted by msev View Post
Dennis I took a look at the audio-modem code...basically this is just the protocol for sending the data right, there are not yet any routines yet added to extract data from the gps right? Will you add it? so the data will go out from one of the analog pins right..I already layed out one more..
and the data would go to audio in on the vtx right?
An Arduino can only output high or low - nothing else. That's why we use a square-wave output instead of a sine. I can't remember what pin I used for PWM output, but the Atmega 328 supports a few pins for hardware-generated PWM output. Sorry to say, but it's not any of the analogue pins

Yes, it's just the send/receive part that's included in the sketch. But as the transmitting part accepts a string, you can just update the string in the GPS-handler, set a flag high to indicate the data is ready, and the audio-modem will transfer the string. At least, that's how I would do it.

Quote:
Originally Posted by rimshotcopter View Post
Here is what I believe would be a good way of connected the Arduino to the Sound/audio signal of the transmitter. Substitute the speaker for the audio-in on the transmitter.

http://arduino.cc/en/Tutorial/Tone

Of course, we need to develop a scheme for sending the data. Decoding I am still working on that.
I would AC-couple the PWM output and preferable use a voltage-divider instead of just a current-limiter/series resister. The AC-coupling might not be necessary, but the voltage-divider will allow you to match the signal to the required/optimal signal level for the audio-input of your video-transmitter.
Apr 02, 2012, 10:58 AM
Registered User
rimshotcopter's Avatar
Quote:
Originally Posted by Dennis Frie View Post

I would AC-couple the PWM output and preferable use a voltage-divider instead of just a current-limiter/series resister. The AC-coupling might not be necessary, but the voltage-divider will allow you to match the signal to the required/optimal signal level for the audio-input of your video-transmitter.
There is 100ohm resistor inline, the value can be adjusted of course.


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Diy osd karl k FPV Talk 2 May 03, 2011 12:31 AM
Idea New DIY OSD? atari7202 FPV Talk 1 Mar 25, 2011 12:08 AM
Discussion see my own diy OSD video Passion Aerial Photography 7 May 27, 2010 01:28 AM
Discussion REAL homebrew DIY OSD - Check it out! jafoca FPV Talk 8 Jun 29, 2009 06:52 PM
Discussion picoOSD DIY PIC12F683 based OSD in C kbosak FPV Talk 6 Jan 31, 2008 07:47 AM