gps downlink using audiochan, which oscope?

[Jack_LaLanne]

I would like to obtain an oscilloscope for learning purpose and the following project:
I have an audio/video downlink in my plane based on airwave modules(awm633 awm635). One audio channel is not used. I want to make a telemetry downlink using it. This means I must modulate the gps serial signal for use with the audio channel and demodulate on the receiver side back into serial. I would like to use ne555 for this.
The thing is my budget is not infinite i.e. I cannot spend 400GBP on this. The bottom line is, what is the minimum required device/features for my purposes? I have seen usbscope on ebay for 60EUR.

Mark_O said a software oscilloscope using computer's soundcard would be suficient. But I'm not sure about that. Don't want to fry my computer.

I have spotted this: http://www.dpcav.com/xcart/product.php?productid=16330&cat=254&page=1
would this device also be suiteable for analysing ppm signal? (maybe I want to make uhf rc link in case of success with the downlink)

thanks in advance

luke

[jeffs555]

That would be ok for just looking at a PPM signal or a low speed audio signal and it does have a higher sampling rate than a sound card. The main problem is that it is only single channel and doesn't have external trigger input. When debugging, it helps a lot to be able to look at the input and intermediate points in the circuit at the same time to see where the signal is being lost. Even a single channel with external trigger would let you trigger on the the input signal so you had a good trigger(very important with a digital scope) and then probe the rest of the circuit.

For a sound card oscilloscope, you can build a simple resistive divider with protection diodes to protect the PC from excessive voltage. http://www.trash.net/~luethi/radiocontrol/circuits/osziconn/connect.html
Even better would be an op amp buffer which would match the high impedance of a real probe to the relatively low input impedance of the soundcard.
http://www.geocities.com/~uwezi/electronics/projects/soundcard_osci.html

[darkith]

There's a new version of firmware for the JYEtech scope that includes external trig:
http://www.jyetech.com/en/default.html

# Higher real-time sampling rate - 5Msps (5Msps works in AUTO mode only)
# Significant faster display refresh rate
# External trig is now available
# Save up to 6 captures to EEPROM and retain after power down
# Retrieve and display saved captures
# Transfer its screen to PC as bitmap file via serial connection

D.

[Jack_LaLanne]

Still trying to find out what trigger is. With it available, it seems to me the only downside of the jyetech device is the lack of multiple channels. I think I can live with that at the beginning.
Somebody knows if those can be obtained inside the european union?

[jeffs555]

There's a new version of firmware for the JYEtech scope that includes external trig:
That would make it much more useful and probably well worth the very low price(50 USD). Put it in a box with a battery and it would be very handy for field work. I saw one review that said the firmware for the onboard AVR was open source. Do you know if that is so?

[darkith]

I looked, and couldn't find it. The Jyetech site doesn't mention that it's open source.
Perhaps somebody got confused that the firmware is freely updatable. :P

Yeah, it looks like a decent portable scope for pretty cheap. I'm seriously considering getting one since he added the "download to pc" option and higher refresh rate.

D.

[Ron W3FJW]

Keep in mind that it's $23US shipping. There's an outfit that's selling it in the states ~$5 shipping. If I can dig out my invoice I'll add it to the thread.
Nice that they've added a front panel to it.

[jeffs555]

Ron,
Do you have one? If so would appreciate your impression of it. I am thinking about getting one and putting it in a case with some batteries to carry in my toolbox.

Jeff

[mcmatrix]

You may buy it from http://www.seeedstudio.com/depot/digital-storage-oscilloscope-with-panels-p-167.html

This shop has better shipping rates to EU countries than http://www.jyetech.com

[Jack_LaLanne]

Thanks a lot for the different thoughts on this. I will be ordering one from seedstudio website.