Laser communication

[thermistor-guy]

...
http://ronja.twibright.com/

Another vote for the LED-based RONJA project. I suggest the OP check it out.

[soldar]

different mag,same idea

Thanks for the link! I am downloading the PDFs. Love them!

https://www.worldradiohistory.com/UK/

https://www.worldradiohistory.com/UK/Hobby-Electronics/

[coppercone2]

that is how house Atradies got destroyed on Arrakis

[DavidKo]

Laser or optical data transmission is very directional or big output power is needed. Small vibrations or misalignment can cause the drop in connection (fog, rain, smoke, birds, spider nets etc. should be considered too).

btw. RONJA was there before WiFi and really never catch up.

[SScattered]

Hi everyone, thanks for all your replies. I thought that I will use an enclosed cover for the laser and receiver so the laser will not ever escaped out of it.

[SScattered]

I currently have a system that I've already built. I used 2 ESP32s as sender and receiver. So the with the current system I send data from Micro SD to receiver which writes data to Micro SD on the receiver.
I want to do manchester encoding and hamming coding so I thought use of FPGA for this task would be quite good and give me better results and speed.

The most important factor for the bandwidth you can achieve will be more down to how you are sending the data, not necessarily how many layers of redundancy and error correction you add.

How are you currently sending the data? If you are just using simple On Off Keying (OOK), then that will be your fundamental limitation. The ESP32 modules don't have very stable or accurate clocks.
 

Yes correct. I'm currently using On Off keying.

[SScattered]

ESP32 -> RJ45 -> http://blog.svenbrauch.de/2017/02/19/homemade-10-mbits-laser-optical-ethernet-transceiver/
http://ronja.twibright.com/
I would assume that the ESP32 is quite capable of reaching better datarates than what youre achieving right now and a FPGA is overkill, but thats just a guess.

I looked into that post. It's astonishing work done by him. Thanks for sharing that.

[LM21]

Don't know about FPGAs but since you know about electronics, did you measure your data from your optics receiver with an oscilloscope. 74kbauds is not much.  A simple laser pointer is visible at long distance  or  at high data rate. But modulation and demodulation may be a problem.

[unseenninja]

I currently have a system that I've already built. I used 2 ESP32s as sender and receiver. So the with the current system I send data from Micro SD to receiver which writes data to Micro SD on the receiver.
I want to do manchester encoding and hamming coding so I thought use of FPGA for this task would be quite good and give me better results and speed.

The most important factor for the bandwidth you can achieve will be more down to how you are sending the data, not necessarily how many layers of redundancy and error correction you add.

How are you currently sending the data? If you are just using simple On Off Keying (OOK), then that will be your fundamental limitation. The ESP32 modules don't have very stable or accurate clocks.
 

Yes correct. I'm currently using On Off keying.

Then a modulation scheme where the receiver can derive its decoding clock from the transmitter's signal will remove a lot of possible mismatch situations. As jbb suggested, a scheme which involves amplitude modulation rather than OOK, would also help and go along with the receiver not having to depend on its clock being the same as the transmitter's clock.

[CaptDon]

Just for a reality check, There is a high power laser link from Muddy Run Pumped Storage to Peach Bottom Power plant 1.5 miles across the Susquehanna River. It is Co2 and thus invisible. Both T/R links are on towers. My guess is they run about 1 watt of optical output power. On both of them you can see a red filter glass on the front.

[jbb]

… I think you’ll need some kind of timing recovery whatever you do. You’ll need to find the bit (technically symbol) edges and also which bits belong to each byte.

The old work project I worked on used 8b/10b coding, which provides:
- DC balance
- separate control codes outside 0-255, which is very helpful for protocol work (no data escaping or stuffing)
- some options for synchronisation words

The receiver can keep watch for the synchronisation words. If you’re using an FPGA or similar, a digital correlator could work well.

https://en.m.wikipedia.org/wiki/8b/10b_encoding

[SScattered]

… I think you’ll need some kind of timing recovery whatever you do. You’ll need to find the bit (technically symbol) edges and also which bits belong to each byte.

The old work project I worked on used 8b/10b coding, which provides:
- DC balance
- separate control codes outside 0-255, which is very helpful for protocol work (no data escaping or stuffing)
- some options for synchronisation words

The receiver can keep watch for the synchronisation words. If you’re using an FPGA or similar, a digital correlator could work well.

https://en.m.wikipedia.org/wiki/8b/10b_encoding

Hi, thanks for replying. I'll look into that.

[SScattered]

Don't know about FPGAs but since you know about electronics, did you measure your data from your optics receiver with an oscilloscope. 74kbauds is not much.  A simple laser pointer is visible at long distance  or  at high data rate. But modulation and demodulation may be a problem.

No, I didn't though. I had no much time recently to check on it. Yeah, I was using on-off keying. I guess that's the issue. I was thinking to build a circuit to control the intensity of the laser like in the link @Echo88 provided