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short range (<cm) full duplex IR data exhange?
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max_torque:

--- Quote from: mikeselectricstuff on April 17, 2019, 11:19:48 am ---
Forget full-duplex - witha free-air link you will always get reflections -  if necessary ping-pong at a higher rate to get the same result

--- End quote ---

This is why i as looking at using a different TX and RX frequency in order to fully discriminate against cross talk   :-+
langwadt:

--- Quote from: max_torque on April 17, 2019, 06:26:59 pm ---
--- Quote from: mikeselectricstuff on April 17, 2019, 11:19:48 am ---
Forget full-duplex - witha free-air link you will always get reflections -  if necessary ping-pong at a higher rate to get the same result

--- End quote ---

This is why i as looking at using a different TX and RX frequency in order to fully discriminate against cross talk   :-+

--- End quote ---

for light that would have to be different colors of light
ogden:

--- Quote from: max_torque on April 17, 2019, 06:26:59 pm ---
--- Quote from: mikeselectricstuff on April 17, 2019, 11:19:48 am ---
Forget full-duplex - witha free-air link you will always get reflections -  if necessary ping-pong at a higher rate to get the same result

--- End quote ---

This is why i as looking at using a different TX and RX frequency in order to fully discriminate against cross talk   :-+

--- End quote ---

Very bad idea. You can discriminate crosstalk only by discriminating optical paths. Half duplex IRDA can reach TX/RX speeds you are looking for, so take it as it is. Consider that those who made IRDA knew what they are doing - they made it half-duplex for a very good reason.
eliocor:
If you want to use the same optical path, and mantain a full duplex communication, your only solution is using different IR light wavelengths: 850nm and 940nm, followed by optical filters on the receivers. 
For your tests, start with known good one filters (expensive!): 
https://www.edmundoptics.com/f/traditional-coated-700-1650nm-bandpass-interference-filters/13917/ 
once done, you can test with cheaper (but not always available and of [maybe] shady quality) ones, like:
https://www.aliexpress.com/item/940-Nm-Infrared-Narrowband-Filter-NBP940-Half-width-40-Nm-Bandwidth-8-8-0-55mm-0/32982732595.html 
https://www.aliexpress.com/item/High-quality-IR-coated-film-filter-band-pass-850nm-laser-transmissivity-92-black-glass-filter-infrared/32864007904.html 
 
If the bandwidth of your filters is too narrow, you have to take care about emitter wavelength shifts do to temperature changes
pwlps:

--- Quote from: eliocor on April 17, 2019, 09:49:32 pm ---If you want to use the same optical path, and mantain a full duplex communication, your only solution is using different IR light wavelengths: 850nm and 940nm, followed by optical filters on the receivers. 

--- End quote ---

The "only solution" is a bit exaggerated and discouraging for the OP's project.  The FSK demodulation bandwidth is controlled by the loop filter time constant so that there is a of course a tradeoff between the frequency selectivity and the maximum bitrate, in other words sacrifying the bitrate you can have as many FSK channels as you want in a single IR wavelength channel. 
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