I'm connecting the PPM output of Phil's encoder to the Mic input of my laptop

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FBMinis
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Joined: 25 Feb 2018, 17:59

I'm connecting the PPM output of Phil's encoder to the Mic input of my laptop

Post by FBMinis » 22 Sep 2018, 20:15

I'm doing this to use the following software so can play Picasim using my transmitter.

http://www.smartpropoplus.com/site/

It's working but the levels seem too be too high. I'm measuring nearly 300mV on the PPM output of the encoder, is this as expected? I wonder if I need to put a voltage divider before the mic input.

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Phil_G
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Re: I'm connecting the PPM output of Phil's encoder to the Mic input of my laptop

Post by Phil_G » 22 Sep 2018, 20:36

Hi Francesco, the PPM output is the full 5 volt logic level from the Atmel processor, which is far too high for a microphone input :)
Typically a mic produces just a few millivolts, so I'd suggest a divider of 1:1000, say 100k and 100 ohms as a starting point. The low impedance will help keep the noise down.

I saw your question on RCG, you could send PPM info via bluetooth, even at the default 9600 baud you could send several 16 bit values within the 20ms frame. You'd need to extract the channel values, send each as 2 bytes over BT then at the receiving end convert these values back to PPM. Hasi's code does both jobs so most of the work is done!

Its worth mentioning that you cant measure the PPM level with a multimeter, its a pulse waveform, you need an oscilloscope ;)
At best a meter will show the average voltage, thats 8 x 300uS / 20000uS x 5v = around 0.6v
Your meter could be missing alternate frames so maybe 0.3v

I wonder if your 'mic input' is actually a 'line input', that would normally be a couple of hundred millivolts. The output of the Atmel chip can only be zero or one, ground or (nearly) 5v as its a digital output.
Does it feed the RF module directly, no resistor, diode or anything inline?
Its possible that the RF module is clamping the level, in which case you need some resistance to drop the
voltage difference - hard clamping can damage the chip (its like partially shorting an output to ground).
If you unplug the RF module does the PPM level from the encoder rise? again remember you cant measure the peak amplitude of a pulse waveform with a multimeter... ;)

Re Bluetooth, remember you need at least one of the two BT modules to be master AND slave capable.
Some such as the HC06 are slave only so two cannot talk to each other :D

Cheers
Phil

FBMinis
Posts: 36
Joined: 25 Feb 2018, 17:59

Re: I'm connecting the PPM output of Phil's encoder to the Mic input of my laptop

Post by FBMinis » 22 Sep 2018, 21:33

My transmitter runs your encoder at 5V (16mhz 328p Pro Mini), and sends the PPM signal to one of those Multiprotocol modules from RCGroups (also built with a Pro Mini). Everything is working fine and I have good range, no glitches.

Now, using a multimeter and measuring the PPM signal coming out of your encoder, should I be seeing those 5V? I'm only measuring 300mV, I must be overlooking something, in my ignorance.

FBMinis
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Joined: 25 Feb 2018, 17:59

Re: I'm connecting the PPM output of Phil's encoder to the Mic input of my laptop

Post by FBMinis » 26 Sep 2018, 18:58

I followed your suggestion and put a voltage divider after the ppm signal and before the mic input. The author of the emulation software also suggests a similar setup with different values:

Mono_schem.gif

However, both suggestions made my signal undetected.

Connecting the ppm signal directly to the mic input works when I set mic level above 50% but there's always a buzzing sound coming from the speakers/headphones even if I mute those outputs. Still, it works perfectly otherwise and I can play Picasim without a problem, as the game interface offers a calibration system. I will try it in in desktop with line-level input his weekend.

Regarding the ppm-to-bluetooth connection with android, I'm still trying to figure it out. So far I've used HASI's ppm reader to capture the 6 channels and display the values in the serial monitor.
Read_any_PPM_V05.ino
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FBMinis
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Re: I'm connecting the PPM output of Phil's encoder to the Mic input of my laptop

Post by FBMinis » 27 Oct 2018, 01:22

There was a problem with the mic-input of my laptop, I had no problem connecting the cable to the mic-input of my desktop. Smartpropoplus and Picasim are working flawlessly on windows 7.
Mono_schem.gif
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Flynn
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Re: I'm connecting the PPM output of Phil's encoder to the Mic input of my laptop

Post by Flynn » 07 Nov 2018, 14:17

Isn't your mono plug connected backwards? conventionally signals go to the tip and ground to the sleeve

Maybe this is the cause of your buzzing... ground loops are tricky things.

May not be a problem unless the two devices touch each other...... :o
You only ever need two tools....WD40 and duct tape.
If it doesn't move when it should use the WD40 and if it moves and it shouldn't use the tape.

FBMinis
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Re: I'm connecting the PPM output of Phil's encoder to the Mic input of my laptop

Post by FBMinis » 10 Nov 2018, 15:36

The illustration is wrong, I've just noticed too.
I built my adapter properly nevertheless. It's been running fine and lately I've been having fun flying the PSS Spitfire.

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F2B
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Re: I'm connecting the PPM output of Phil's encoder to the Mic input of my laptop

Post by F2B » 09 Feb 2019, 19:45

This must be it:
Flight Sim Adaptor.jpg
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F2B or not to be....

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