Laser communication - Page 1
Forum section: electronics / projects

author: SScattered
author_rank: Contributor
timestamp: March 23, 2024, 07:12:15 pm
content: Hi,Recently I've built a system where I can send data using a laser. This system uses 2 ESPs as the sender and receiver. It's short range and I only tested around 1m gap between laser and receiver. I thought of giving another shot for this project using FPGAs. I boughtTang Nano 9K FPGAbut I'm new to FPGAs. I learned some lessons while I was in the uni, but there was no use of FPGAs for me until now.My idea is to implement manchester encoding and hamming(7,4). So, I thought FPGA would give me more data rate. Current data rate is around 74kbit/s, it takes a considerable time to transfer even a 2MB file. Can anybody tell me where should I start and will there be improvement of data rate using FPGAs?Also note that Tang Nano 9K has a SD Card slot also, maybe I can use that instead of using a microcontroller with FPGA to store data there?PS: I don't use fiber optic. This is going to be short range free-space optical communicationPS: I'm an electrical & electronic engineer

author: tggzzz
author_rank: Super Contributor
timestamp: March 23, 2024, 08:01:39 pm
content: Whatever you do, makevery surethat itcannotblind people passing by,even when there is a gross failure in the system. For the avoidance of doubt, I don't care if you blind yourself.What happens if the laser is turned on permanently? Or the current through the laser is too high? Or the optics are knocked/damaged?Make sure you understand the eyesafety limits; many lasers on the market exceed those by a factor of 100 or 1000

author: jonpaul
author_rank: Super Contributor
timestamp: March 23, 2024, 10:52:45 pm
content: simpler with fiber optic. Toshible TOS-LINK etc,j

author: moffy
author_rank: Super Contributor
timestamp: March 23, 2024, 11:32:23 pm
content: As jonpaul mentions, fiber optics is easier because one can buy integrated packages with all of the optics and drivers built in. If you want to go free air then you will probably need to look at collimating lenses and your own driver and receiver. Optical communication starts with a fast LED/Laser and driver and a fast low noise receiver, possibly using a PIN diode. The optics and filtering are as important as the transmitter and receiver. Once you have the physical link established then you can look at the data transmission and reception protocols. So is 1mm the physical link distance you are looking for or do you plan to use it in some other application? And as tggzzz mentions eye safety is a critical factor and if you can stay for lasers at or below 1mw you are better off.

author: coppercone2
author_rank: Super Contributor
timestamp: March 24, 2024, 12:45:37 am
content: I have a feeling you don't need power unless you need to get through rain.Good optics reduce the power requirement drastically.It made me wonder if an array of low power lasers might work in rain, since maybe one of the beams will have better integrity for a short amount of time with a random distribution of rain droplets. Fog might be the bigger problem.What you need for safe experiments on lasers in open environment1) heavy support structure. Not some dinky tripod with ball joints that barely fit, I mean that you need to tighten down a big bolt2) mechanically seated components (i.e. glue joint failing won't let a optic get out of the safe zone)3) operating area is smaller then safe zone so you can account for things like optics becoming dislodged etc'what is a bad idea is doing this in a metropolitan areaAlot of optics are just glued ,which is obviously a problem because super glue or epoxy can fail.For making high power lasers safe, IDK. I think you just need everyone that can be effected to wear goggles. Even if you have a rugged hardware setup, its still possible for glass to fracture and allow a beam to go into basically a random direction. Long shrouds over the output of the laser might help restrict it, but really that IMO needs to stay in a physics lab.Making safe links for consumers at high power levels is probobly never gonna be a reality because joe dumbarse is going to want to know if the thing is down and look down the optic output to see if the 'bulb is weak or somtin'

author: tggzzz
author_rank: Super Contributor
timestamp: March 24, 2024, 01:52:41 am
content: Quote from: coppercone2 on March 24, 2024, 12:45:37 amCorrect. Then define everyone thatcouldbe affected, and how youwill ensurethey wear goggles.Good luck with that!QuoteNever forget specular reflections; they make beams go round corners, through open doors etc.QuoteYup.

author: coppercone2
author_rank: Super Contributor
timestamp: March 24, 2024, 02:47:58 am
content: could a large grid of low power lasers help deal with rain related losses if some algorithm was applied to maintain safety?

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 24, 2024, 04:07:25 am
content: I recall there was a project a long time ago to run 10Mbps Ethernet over laser pointers.

author: daisizhou
author_rank: Super Contributor
timestamp: March 24, 2024, 07:41:42 am
content: Can you share some details?Although the fiber optic connection is good, it is a wired connection, which is very inconvenient.I'm very interested in your project

author: tggzzz
author_rank: Super Contributor
timestamp: March 24, 2024, 09:15:10 am
content: Quote from: NiHaoMike on March 24, 2024, 04:07:25 amTAoE section 9x.23 is "Sending power on a beam of light".They note the producthttps://www.lumentum.com/en/products/diode-laser-830-nm-fiber-coupled-2w-2486-l4-seriesThe datasheet contains this. Noteallthe words

author: SScattered
author_rank: Contributor
timestamp: March 24, 2024, 09:19:08 am
content: Quote from: tggzzz on March 23, 2024, 08:01:39 pmHi, thanks for the reply! Yeah, for sure. Currently I'm using a 5mw red-laser diode. My current testing distance will be around 1m so when I increase the distance I sure will need the lenses.So I think with this laser and the distance it's not much of an issue to do testings?

author: SScattered
author_rank: Contributor
timestamp: March 24, 2024, 09:22:49 am
content: Quote from: moffy on March 23, 2024, 11:32:23 pmYes, it will be short range free-space optical communication. The laser diode I have is 5mW (mentioned in the website tho)

author: SScattered
author_rank: Contributor
timestamp: March 24, 2024, 09:30:27 am
content: Quote from: coppercone2 on March 24, 2024, 12:45:37 amThe laser diode is 5mW red laser. This will be a short range free-space optical communication. My first concern is to get this working between couple of meters. I want to achieve higher bit rates, that's why I thought I'd use FPGAs.Thanks! Yeah, I understand the very dangers when it comes to lasers. One mistake with a high powered laser, you are blind next second. But still I've no intention of going for high power laser. I will stick to 5mW diode and see where it can take me. Even if it's couple of meters I'd be happy to have higher bit rates

author: SScattered
author_rank: Contributor
timestamp: March 24, 2024, 09:41:49 am
content: Quote from: daisizhou on March 24, 2024, 07:41:42 amI've already mentioned it in the first post. Anyway, I'll try to explain it again.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.Please see the attached image. The cover and everything is designed and 3D printed.

author: tggzzz
author_rank: Super Contributor
timestamp: March 24, 2024, 10:25:35 am
content: Quote from: SScattered on March 24, 2024, 09:19:08 amWhat I (and you)thinkis completely and utterly unimportant and irrelevant.What matters is what actually happens.You need to be sure that it cannot output dangerous levelsunder anyfaultconditions, e.g.too high a current, or an inaccurate specification.Feel free totest it on your eyeballs.Do not test it on other people's eyeballs.I am very deaf. If I go blind for any reason whatsoever, then Iwillcommit suicide. Seriously, no joke. Hence I'm sensitive to such "hopeful guesses".

author: unseenninja
author_rank: Regular Contributor
timestamp: March 24, 2024, 10:49:50 am
content: Quote from: SScattered on March 24, 2024, 09:41:49 amThe 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.

author: moffy
author_rank: Super Contributor
timestamp: March 24, 2024, 10:51:34 am
content: Quote from: SScattered on March 24, 2024, 09:22:49 amI think you should start with a collimating lense, as the optical power coupled to the receiver without collimation will drop off very quickly. You should also practice the alignment process between transmitter and receiver, it gets trickier with distance.

author: madires
author_rank: Super Contributor
timestamp: March 24, 2024, 12:53:24 pm
content: A 5mW laser would be laser class 3R which requires some safety measures. With appropriate optics (diverging, spreading) it could become class 1M (fairly safe). Commercial FSO systems are usually class 1M.

author: cncjerry
author_rank: Unknown
timestamp: March 24, 2024, 01:28:50 pm
content: 5mw is enough to cause serious retinal damage from a reflection, especially if you are aiming at a metal canned detector. You dont need a laser to get distance, you just need an LED, think remote control, but it has to be modulated for detection improvement. Switching it on and off is not enough, you have to modulate the signal, think lock-in amplifier. That will improve your distance tremendously.

author: madires
author_rank: Super Contributor
timestamp: March 24, 2024, 01:53:16 pm
content: I agree, 5mW is way too much for a few meters. And there's also the LOS problem (line of sight). A better solution would be LiFi (https://en.wikipedia.org/wiki/Li-Fi) which can achieve surprisngly high data rates.

author: MarkT
author_rank: Frequent Contributor
timestamp: March 24, 2024, 06:40:16 pm
content: QuoteJust into class 3B - you should be thinking class 1, less than 0.39mW visible unless you have a really good reason for more power. 0.3mW is millions of photons per nanosecond, to put into context, quite capable of high-speed signalling with suitable emitter and receiver.

author: jbb
author_rank: Super Contributor
timestamp: March 24, 2024, 09:33:08 pm
content: I can’t go into too many details, but some years ago I worked on a system which got some MBit/s over a 1 meter air gap using infrared LEDs and On-Off-Keying.Encoding was 8b/10b without forward error correction.Receiver used an IR photodiode and transimpedance amplifier. It used an FPGA LVDS input port as a comparator, I think…I didn’t dig into the analog guts, but I suspect the on off keying was suboptimal, because LED turn off was likely a bit slower than its turn on (ie it was asymmetrical). Maaaybe it’d be better to switch the light source between a high (100%) and low (10% ??) current source so it’s always conducting?

author: soldar
author_rank: Super Contributor
timestamp: March 24, 2024, 11:57:37 pm
content: Just as a curiosity I will mention that many years ago Elektor magazine had a project which modulated a halogen light (a car's headlight) and, if I remember correctly, could send voice over a mile. The filament is so hot that it has low enough thermal inertia and can be modulated.

author: Echo88
author_rank: Frequent Contributor
timestamp: March 25, 2024, 12:20:27 am
content: 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.

author: themadhippy
author_rank: Super Contributor
timestamp: March 25, 2024, 12:38:24 am
content: Quotedifferent mag,same ideahttps://www.worldradiohistory.com/UK/Hobby-Electronics/Hobby-Electronics-1978-12.pdf

author: thermistor-guy
author_rank: Frequent Contributor
timestamp: March 25, 2024, 07:49:41 am
content: Quote from: Echo88 on March 25, 2024, 12:20:27 amAnother vote for the LED-based RONJA project. I suggest the OP check it out.

author: soldar
author_rank: Super Contributor
timestamp: March 25, 2024, 10:34:03 am
content: Quote from: themadhippy on March 25, 2024, 12:38:24 amThanks for the link! I am downloading the PDFs. Love them!https://www.worldradiohistory.com/UK/https://www.worldradiohistory.com/UK/Hobby-Electronics/

author: coppercone2
author_rank: Super Contributor
timestamp: March 26, 2024, 01:38:35 am
content: that is how house Atradies got destroyed on Arrakis

author: DavidKo
author_rank: Frequent Contributor
timestamp: March 26, 2024, 09:59:04 am
content: 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.

author: SScattered
author_rank: Contributor
timestamp: March 27, 2024, 05:06:23 am
content: 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.

author: SScattered
author_rank: Contributor
timestamp: March 27, 2024, 05:07:55 am
content: Quote from: unseenninja on March 24, 2024, 10:49:50 amYes correct. I'm currently using On Off keying.

author: SScattered
author_rank: Contributor
timestamp: March 27, 2024, 05:24:53 am
content: Quote from: Echo88 on March 25, 2024, 12:20:27 amI looked into that post. It's astonishing work done by him. Thanks for sharing that.

author: LM21
author_rank: Regular Contributor
timestamp: March 27, 2024, 05:41:09 am
content: 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.

author: unseenninja
author_rank: Regular Contributor
timestamp: April 06, 2024, 09:03:30 pm
content: Quote from: SScattered on March 27, 2024, 05:07:55 amThen 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.

author: CaptDon
author_rank: Super Contributor
timestamp: April 07, 2024, 03:18:52 am
content: 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.

author: jbb
author_rank: Super Contributor
timestamp: April 07, 2024, 05:00:03 am
content: … 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 wordsThe 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

author: SScattered
author_rank: Contributor
timestamp: April 15, 2024, 03:26:25 pm
content: Quote from: jbb on April 07, 2024, 05:00:03 amHi, thanks for replying. I'll look into that.

author: SScattered
author_rank: Contributor
timestamp: April 15, 2024, 03:30:28 pm
content: Quote from: LM21 on March 27, 2024, 05:41:09 amNo, 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