Tiny Telemetry - DOA?

[a_marmot]

IRC aficionados:

I've been trying to install a TinyTel in a small FPV plane. Got everything put together, and confirmed power to the TinyTel, but observe no audio stream at the receiving end.

Unfortunately my bench testing is being conducted in an area with no sky access. Should the TinyTel send out an audio signal with non-GPS telemetry (like battery voltage) before it acquires a satellite lock? Or is it completely silent until it gets a lock, and then broadcasts all the data?

The answer to this question will effect my next move in the diagnosis process.

Thanks!

[ssassen]

Yes, it always sends telemetry, even when no GPS lock has been acquired, how do you have it wired in? A picture, or a clear description, would be helpful.

[a_marmot]

OK, I'll poke around with an oscilloscope to see if and where the signal is getting lost. What should the audio waveform look like (amplitude, approximate width of pulses)?

I've got the VCC and ground wired to an unused servo channel (which seems fine since the unit is getting power). Battery voltage +/- is wired to the appropriate ports on the TT. I have not installed the current sensor, so that port is left unconnected. The audio is routed directly to the audio input of the VTx, which has a power supply sharing the same universal ground as the battery and UHF Rx. I'll send a picture later if it becomes necessary.

[a_marmot]

Sander-

OK, I have traced at least part of the problem. The TinyTelemetry is producing a dc coupled 0-1.5 volt square waveform on the audio output. It looks totally clean going into the ReadymadeRC 100 mW 1280 MHz VTx. However, at the receiving end, the audio output from a Lawmate 1280 MHz VTx is not square. It looks like the attached.



As you can see, the amplitude is quite high (+/- 3V), which is TOO LOUD (as reported by both EzAntennaTracker and iTelemetryFPV). Note also the audio has it has lost its square waveform. I realize the transmitter and/or receiver are going to limit the bandwidth of the audio to below some cutoff frequency. However, you can see the time constant of the cutoff is competitive with the data bandwidth. I've repeated this with two different lawmate receivers, same result.

What is odd is that this exact same VRx was used with an EzOSD, and I could get telemetry just fine. It's only the TinyTel with this problem. Is it possible the TinyTel produces an audio signal with too large an amplitude, which is saturating the audio input of the VTx? I haven't measured the EzOSD, do you know offhand if the EzOSD and TinyTel differ in the amplitude of their audio signals?

[a_marmot]

Sorry, one more (cosmetic?) issue: the latest iTelemetryFPV app has a bug. If you end a mission, and then start a new one, the number of good and bad packets reported in the "Telemetry Link" section does not reset. There seems to be no way to flush this data and restart the stats.

[ImmersionRC]

The signal on the scope picture looks fine, we've seen much worse :-)
The modules used for our 5.8GHz links, and also the 2.5GHz links, have a superb audio performance, so with a square-wave in, that's basically what you get out.

For other modules, for example Lawmate, there is a large variance between modules. It appears that the designers couldn't make up their minds on what the audio pre/de-emphasis specs should be, so, as an example, the 500mW lawmate 2.4Gig matches very well with the black lawmate Rx, but the 1W Tx is not a good match at all.

Anyway, this isn't your problem here, download the latest ImmersionRC Tools from here:
http://www.immersionrc.com/betaville.htm

On the tinyTelemetry configuration page there is a level control. This controls the audio level, and can be used to lower the amplitude.

Hope this helps,
Team IRC

Sander-

OK, I have traced at least part of the problem. The TinyTelemetry is producing a dc coupled 0-1.5 volt square waveform on the audio output. It looks totally clean going into the ReadymadeRC 100 mW 1280 MHz VTx. However, at the receiving end, the audio output from a Lawmate 1280 MHz VTx is not square. It looks like the attached.

Attachment 3740

As you can see, the amplitude is quite high (+/- 3V), which is TOO LOUD (as reported by both EzAntennaTracker and iTelemetryFPV). Note also the audio has it has lost its square waveform. I realize the transmitter and/or receiver are going to limit the bandwidth of the audio to below some cutoff frequency. However, you can see the time constant of the cutoff is competitive with the data bandwidth. I've repeated this with two different lawmate receivers, same result.

What is odd is that this exact same VRx was used with an EzOSD, and I could get telemetry just fine. It's only the TinyTel with this problem. Is it possible the TinyTel produces an audio signal with too large an amplitude, which is saturating the audio input of the VTx? I haven't measured the EzOSD, do you know offhand if the EzOSD and TinyTel differ in the amplitude of their audio signals?

[a_marmot]

Awesome, I'll try it, thanks.

Out of curiosity, why did you guys decide to go with AM audio for the telemetry instead of FM audio? I'd think that alternating tones (e.g 2000 and 3000 Hz) would get through even the crapiest of audio devices, with amplitude totally irrelevant.

[a_marmot]

Nope - denied. TinyTelemetry is not recognized by ImmersionRCTools as a device, so cannot read or change configuration. Any suggestions?

[a_marmot]

Update: I installed the latest version of IRCTools (1.13), and followed the onscreen instructions to install the device driver. Oddly it appears as "ImmersionRC USB to UART (COM3)" rather than as "TinyTelemetry". In any case, even with the device driver installed and the device appearing in the COM Port pulldown menu, IRCTools still cannot communicate with the device, error reported is "Failed to communicate with device".

[a_marmot]

Sander-

Is there a way to communicate with TT via unix command line?