cutting opto coupler in half? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: August 10, 2025, 01:29:42 am
content: So it occurred to me that a opto coupler chip is well tested and has good drive electronics and its well built.Is it possible to cut one of these chips in half so that you can built a adapter to a fiber optic wire? The ones I have seen have a diagonal design that would make it hard to cut in half. But it looks like you might be able to salvage half of each one and connect them to make a poor mans fiber transmitter using only crude tools. Or perhaps just drill a hole in it to connect it to another one with a fiber?Has anyone done experiments like this? For fun, I already have IR photodiode IC's that can be easy to hook into a fiber wire.Everyone must have lots of useless shoddy opto's in their junk box since time immemorial. My idea was to use a diamond disk on a dremel to try to access the optic area, and maybe polish something and cast some kind of lens from resin.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 10, 2025, 02:56:31 am
content: Many optos have up/down leadframes, rather than side by side, so good luck cutting that !You can buy side looking LED and PhotoTX which can be placed face to face to create an opto coupler, = easier thangetting out the saw!

author: coppercone2
author_rank: Super Contributor
timestamp: August 10, 2025, 03:31:02 am
content: if you separately grinded two of them down do you think they would interface with each other OK or are they matched by package?I really think you can get at least 1 side salvaged if you try hard enough

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 10, 2025, 03:35:32 am
content: Quote from: coppercone2 on August 10, 2025, 03:31:02 amThat's a lot of labour, which much be very cheap to even attempt this.Yields would be low, and then you still need to somehow couple the working halves to your fiber, without damaging the exposed area.

author: ejeffrey
author_rank: Super Contributor
timestamp: August 10, 2025, 03:56:49 am
content: It sounds like what you want is a toslink transmitter and receiver. For the extra couple dollars you get a device that is mechanically and optically designed to actually do this. It has moderately high bandwidth too.

author: John B
author_rank: Frequent Contributor
timestamp: August 10, 2025, 04:26:03 am
content: Quote from: ejeffrey on August 10, 2025, 03:56:49 amYes and they're reasonably cheap. I've fixed and salvaged a lot of discarded gear because the plastic male/female connectors wear out and no longer click together. So maybe not great for many connection/disconnection cycles.

author: Andy Chee
author_rank: Super Contributor
timestamp: August 10, 2025, 06:32:34 am
content: Quote from: coppercone2 on August 10, 2025, 01:29:42 amMy question is;Where are you getting the fiber from?One would presume that if one has access to surplus or salvaged fiber, one would have access to better means of interfacing it.My low cost fiber interface technique is to salvage TOSLINK transmitters/receivers from discarded e-waste DVD players and DTV set-top boxes.

author: MAS3
author_rank: Regular Contributor
timestamp: August 10, 2025, 08:18:42 am
content: Quote from: coppercone2 on August 10, 2025, 03:31:02 amPerhaps.Just for the experimental side of it.But it will take many tries.After grinding you'd have to do some polishing in order to keep focus of the light.And you'd need to do some matching to get the light to hit right spot at the receiver side.All these steps would need to be done at both sides, and with any set you'd want to create.Also, a lot more effort would be necessary if you'd like to have any transmitter to connect to any receiver.Again: nice to see if it could be done, unlikely to reach a sensible use for this rather than using suggested alternatives.

author: SteveThackery
author_rank: Super Contributor
timestamp: August 10, 2025, 10:18:55 am
content: Maybe start out with a slotted optocoupler?

author: BILLPOD
author_rank: Frequent Contributor
timestamp: August 10, 2025, 01:48:34 pm
content: Maybe fellow memberNoopy, has, or can provide photos of the insides of one of these optocouplers,Hey Noopy, are you 'listening'?

author: macboy
author_rank: Super Contributor
timestamp: August 10, 2025, 04:42:41 pm
content: I like Steve's idea, if the signal needs to be analog.If I needed a digital signal, I would just use Toslink as suggested by others, since I have nearly as many of those modules in my junk box as optos. I guess that reveals what kind of devices I tend to find and part out.

author: Andree Henkel
author_rank: Regular Contributor
timestamp: August 11, 2025, 01:32:51 pm
content: About 15 years ago I was visiting a german fusion reactor research institute (at Garching near Munich).I had a job offer as electronics engineer there.They showed me samples where they have done just that:Cut analog optocoupler based isolation amplifier in half to achieve larger isolation voltage.And these parts are (were) in actual use at their research fusion reactor.

author: coppercone2
author_rank: Super Contributor
timestamp: August 11, 2025, 01:37:58 pm
content: did they say how they cut it? It sounds better funded then me

author: Andree Henkel
author_rank: Regular Contributor
timestamp: August 11, 2025, 01:58:33 pm
content: can´t remember if they told me that in detail, they showed me cut samples and pcb´s where the parts were used.

author: mtwieg
author_rank: Frequent Contributor
timestamp: August 11, 2025, 02:40:47 pm
content: Last time I looked at the insides of an optocoupler, the LED and photodiode were stacked vertically, with an insulator (probably mylar) in between them. Didn't look like they could be separated without destroying them, and and even if you did, rebuilding it with another medium interface would likely be very difficult. The effective CTR would probably be very inconsistent, and you'd have to worry about interference from ambient light sources as well.You might be interested in this teardown of a HV amplifier from The Signal Path:https://youtu.be/1voyXXpq-k0?si=em2yY7Cr7EvnupZQ&t=2087You can see they made super-high-voltage optocouplers by combining an LED, photodiode, and light pipe. Actually looks quite crude, but I'm guessing there's some trick to getting matched performance between all of the modules.

author: Andree Henkel
author_rank: Regular Contributor
timestamp: August 11, 2025, 03:10:27 pm
content: what I can remember is that the parts they started with had a very large distance between the pin rows to begin with,like the Texas Instruments AMC14xx which have 15,7mm clearance / creepage.for what they did to work, the parts surely weren´t stacked vertically.Which doesn´t mean that Optocouplers for lower isolation requirements cannot be stacked vertically.addition:Well, if I remember right, the cuts were indeed angled, both at the transmitter as well as at the receiving side

author: tooki
author_rank: Super Contributor
timestamp: August 11, 2025, 05:38:32 pm
content: Quote from: coppercone2 on August 10, 2025, 01:29:42 amDo they, though? I thought most optocouplers have a simple LED inside, and are driven just like you would any other bare LED.(I do know there are solid state relays that have actual constant-current drivers for their LEDs, giving them delightfully wide control voltage ranges, but of course they're vastly slower than an optocoupler.)

author: Benta
author_rank: Super Contributor
timestamp: August 11, 2025, 06:26:53 pm
content: It's very simple to identify "stacked" optocouplers vs. "side-by-side".The first are black, the others are white.But cutting a side-by-side is a bad idea, as the white epoxy works as a reflector between emitter and detector.All in all, a futile endeavour.

author: nikolatesla
author_rank: Contributor
timestamp: August 12, 2025, 05:59:28 am
content: I am trying to do this(grinding 3120 driver chips) as well . Complete failure so far.I tried toslink pairs but they use 38khz carrier which made them unsuitable .Im now using the toslink connectors and fibre with laser transmitter and photo diodes ,which is going well so far.Reducing component count and short traces is the goal .I am surprised that a high speed ir driven mosfet does not seem to exist as it makes working with mosfets and high current pulses seem much easier .The amount of stray magnetic fields from a high current pulse can be huge and un predictable ,which makes this project a versatile one . from tesla coils to EV speed controllers ..its a long list .Coax or twisted pairs wont do the job in many cases where the near field is complex.

author: Gyro
author_rank: Super Contributor
timestamp: August 12, 2025, 08:40:23 am
content: I'm puzzled by what you say about Toslink pairs using 38kHz carrier. Toslink transmitters don't use any other modulation than what they are fed with - typically an S/PDIF digital audio stream. This runs much faster (MHz region) and is completely controlled by the S/PDIF transmitter IC. The Toslink transmitter simply contains a logic level input driver for the LED, likewise a logic level output from the receiver.I think you are confusing the 38kHz modulation with IR remote control receivers.I think Toslink transmitters and receivers would be a much better solution for the OP than trying to cut up optocouplers as they already include direct optical fiber connection.

author: TERRA Operative
author_rank: Super Contributor
timestamp: August 12, 2025, 11:44:38 am
content: Why not just drill a hole into the top of a 5mm IR LED and a corresponding IR Receiver 'LED'?Then just poke your optic fiber into the holes.

author: Andree Henkel
author_rank: Regular Contributor
timestamp: August 12, 2025, 03:46:23 pm
content: Quote from: nikolatesla on August 12, 2025, 05:59:28 amexactly huge magnetic fields (fusion reactor plasma enclosure) -> is why they did itand how do you isolation in the >1x.xxxV with coax or twisted pair...

author: tooki
author_rank: Super Contributor
timestamp: August 12, 2025, 08:39:47 pm
content: Quote from: nikolatesla on August 12, 2025, 05:59:28 amI concur with Gyro: I think you’re confusing IR remotes with TOSLINK, because TOSLINK starts at nearly 3 megabits per second and goes up with audio format. A 38kHz carrier simply couldn’t work there (and as Gyro said, TOSLINK (which is S/PDIF over optical) doesn’t use a carrier. In devices with both coaxial and TOSLINK jacks for S/PDIF output, it’s completely common for the same output signal from the decoder IC to drive the coaxial jack directly and use a simple transistor driver to run the TOSLINK output.

author: nali
author_rank: Frequent Contributor
timestamp: August 12, 2025, 09:09:43 pm
content: Some of the audio TOSLINK receivers have min/max data rates e.g. Toshiba TORX147 specifies 100k-15Mb/s, so there's some sort of signal conditioning or data slicing going on in there. So depending on what you want to do with them they may or may not be suitable.https://www.digikey.co.uk/htmldatasheets/production/109667/0/0/1/fiber-optic-devices-toslink-guide.html

author: nikolatesla
author_rank: Contributor
timestamp: August 13, 2025, 01:55:23 am
content: Thanks for that datasheet link.The toslink transmitters i tried gave 38khz out modulated by the data pin .The receivers were raw data.The info on these things so far has been sparse and I also thought that there should be no smarts in the tiny unit but my experience was different from my assumption.It is almost impossible to tell the tx from the rx units as the ones i bought were un marked.I think that its best to try this for yourself and please correct me from that context.I will post here when I have success.

author: coppercone2
author_rank: Super Contributor
timestamp: August 13, 2025, 03:46:57 am
content: the answer to all the questions is because macguyver

author: Andy Chee
author_rank: Super Contributor
timestamp: August 13, 2025, 05:34:56 am
content: If you want to MacGyver an optical fiber link, instead of a top down approach and cutting an existing optocoupler in half, how about building one from bottom up?Attach the fiber directly between a conventional discrete IR LED and discrete IR photodiode/phototransistor, pot the whole thing in opaque potting compound.

author: tszaboo
author_rank: Super Contributor
timestamp: August 13, 2025, 09:04:04 am
content: Why do you always have to do weird things? Seriously, I would like to understand the thought process, instead of using off the shelf parts, instead of that, spending time to epoxy stuff, cut stuff, cold weld stuff, and do all these labor inessive non-repeatable processes to make something.

author: Gyro
author_rank: Super Contributor
timestamp: August 13, 2025, 12:29:44 pm
content: Quote from: nikolatesla on August 13, 2025, 01:55:23 amI can only think that you had the receiver was in line of sight of some 38kHz source, a compact florescent or switching converter LED light for instance, but that's just a guess. Short answer, I don't know where the 38kHz came from in your specific instance, but that is not normal (to spec) behavior.QuoteUnmarked parts is a bad sign, they will either be production line rejects that have 'found their way' out of the factory and onto Aliexpress or wherever, or fakes (though fakes would normally carry some counterfeit marking). Genuine parts would, of course, be properly marked.QuoteI have tried them - developing consumer A/V products that have sold 10s of k per month (sorry to rub it in, but you will find professional engineers of all types on this forum, not just amateurs).

author: nikolatesla
author_rank: Contributor
timestamp: August 13, 2025, 12:36:17 pm
content: In my case ,the goal is to switch some mosfets from a few metres away with isolation that only a light pipe can do.This is a challenge and If only there were optically controlled mosfets for up to 100khz I would use them .Photo diodes are very good rectifiers ,which also need to be addressed with shieldingIf you know of a simple way it would be well receivedThe other reason is that it is challenging and rewarding to try some alternate thinking .Each failure is a reward of sorts .my grinding the opto drivers has failed so far but I will try it again ,this time from the bottom .

author: Gyro
author_rank: Super Contributor
timestamp: August 13, 2025, 12:55:26 pm
content: In that case Andy Chee's suggestion (Reply #26) shows a lot of promise, You can select the transmitter LED for power output and wavelength (TOSLINK's use of red light may not be ideal depending on fibre length and type), you can also select the best photodiode / phototransistor for your drive circuit configuration.Somebody suggested drilling a hole in the ends of the packages for insertion of the fibre close to the die works well, I have done it myself. I remember, many years ago,one manufacturer produced devices with a tiny glass bead in the end of the package to focus light into (and from) the end of a fiber.Note that clean cleaving of the fiber ends has a large effect on light coupling.P.S. I would abandon the grinding of the optocouplers on the engineering basis that the LED is sized to drive the photodiode / phototransistor over an extremely short optical distance. This makes it fundamentally unsuited to driving an optical fiber of a few metres, likewise the sensitivity of the receiver part.

author: voltsandjolts
author_rank: Unknown
timestamp: August 13, 2025, 01:07:00 pm
content: Quote from: nikolatesla on August 13, 2025, 12:36:17 pmErm, inanother post you mentioned 500V supply.Assuming same project your discussing here, you don't need optical fibre isolation for 500V.

author: mtwieg
author_rank: Frequent Contributor
timestamp: August 13, 2025, 01:40:27 pm
content: Quote from: Benta on August 11, 2025, 06:26:53 pmIntriguing! I can't confirm or deny this, but I wonder, if the white epoxy works as a reflector, why wouldn't one use it in both types?

author: tooki
author_rank: Super Contributor
timestamp: August 13, 2025, 06:15:28 pm
content: Quote from: nikolatesla on August 13, 2025, 01:55:23 amPlain and simply, I don't believe that. TOSLINK transmitters are literally just an LED in a really special package. And given TOSLINK's intended purposes, it would make zero sense to modulate at 38kHz, which is simply too slow.It's far more likely you picked up 38kHz interference something, as Gyro said, or were using an infrared remote library and didn't realize it's doing the modulation.

author: tooki
author_rank: Super Contributor
timestamp: August 13, 2025, 06:18:44 pm
content: Quote from: mtwieg on August 13, 2025, 01:40:27 pmThe black epoxy is filled with a lot of mineral compounds to improve thermal conductivity and give it a coefficient of thermal expansion similar to that of silicon. The white stuff is probably much worse than the black stuff in those properties, and probably costlier since it's not used as much. So if you don't need it, you'll probably use the standard black kind.

author: coppercone2
author_rank: Super Contributor
timestamp: August 14, 2025, 02:41:53 am
content: Quote from: Gyro on August 13, 2025, 12:55:26 pmI am not 100% sure but from what I understand the loss from a few meters of fiber line would be in the 0.01 or less dB range. Less then 1%. Of course the coupler is what may kill it. I am nearly certain that if you can get the coupler right, the fiber line length is irrelevant for lab uses.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: August 14, 2025, 04:01:29 am
content: Quote from: tooki on August 13, 2025, 06:15:28 pmThis is definitely possible.I have TOSLINK receivers that do that. If you look in the datasheet you can see that it is designed to receive a NRZ signal with a minimum data rate of 0.1 Mbps:https://www.hy1688.com.tw/SWITCH/DC%20JACK%20HOME/Optical_File/DLR1131.pdfThere is probably some kind of automatic gain control circuit inside, and if there is no signal it will just amplify noise.Are you trying to build a tesla coil? There are already premade controllers on Aliexpress that you can buy which come with the fiber. Just make sure to get one with the inductor for the phase lead.

author: nikolatesla
author_rank: Contributor
timestamp: August 14, 2025, 08:17:47 am
content: Hey,thank you for that link.It seems that there are so many flavors of these unmarked Chinese gems .I will reorder a few different pairs and try the easy (conventional) way again.It a crap shoot with this stuff ,sometimes fake sometimes rejects but sometimes they work as expected.I checked to ones I have again that output bursts of 38 khz ..they still do thatMeanwhile My discrete photo diode venture will continue while I wait my surprise packages from the far east.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: August 15, 2025, 03:54:53 am
content: Quote from: nikolatesla on August 14, 2025, 08:17:47 amI've had luck buying aftermarket HFBR-1414 parts from aliexpress. Just make sure to get the used ones since those are usually salvaged from old stuff (so you know they're real and not fakes).That was years ago though, so I don't know if it's still the same.

author: Gyro
author_rank: Super Contributor
timestamp: August 15, 2025, 09:00:27 am
content: Genuine parts, with datasheets, are so cheap from the main distributors - RS, Farnell, Digikey etc. that I don't understand the gambling with dodgy, unmarked, parts from Ali. Life is just too short and debug time has value.

author: tooki
author_rank: Super Contributor
timestamp: August 15, 2025, 09:47:41 am
content: Quote from: nikolatesla on August 14, 2025, 08:17:47 amAnd if you disconnect the transmitter? Try once with the fiber disconnected from the receiver, and then try once with the receiver covered up with black electrical tape.

author: nikolatesla
author_rank: Contributor
timestamp: August 16, 2025, 06:20:23 am
content: Just a shout out of thanks for the encouragement to check this again.I pulled some toslink connectors from an unused audio interface I had gathering dust and sure enough they do react as originally expected.The ones I had from china had de coding and encoding built in which I ass umed was the norm .Progressing well now .I will post here when I have the mosfets and drivers switching at 100khz. In close proximity to the coil primary.Still need to shield from em noise but now it will be in one known place .The body of these connectors are allegedly made of conductive resin which will help.I'm sure that others may find this useful

author: nikolatesla
author_rank: Contributor
timestamp: August 21, 2025, 04:48:40 am
content: Mosfet driven by Light pipe.The wiring is straight forward with direct coupling from toslink connector to mosfet driver then to the mosfet.Decoupling caps on the mosfet driver are essential as noise will be the result without them. The data sheets explain this.Mic4422 was the mosfet driver I used which will run from 5 volts to 36voltsI used a 9v battery which is fine for logic level Mosfets.You can just double the supply voltage to 18 volts if you need a higher gate voltage. The toslink supply will need to have a 5v regulator.This works up to 1.4 megahertz after which the duty cycle became unequal . This can be fixed by altering the source duty for correct balance but clearly this would be the reliable limit.In my case 33khz was the maximum required at this stage.I also found that my fy8300 3 channel generator was not symmetrical unless cmos output was selected. These are cheap for what you get but have many flaws.One of the other advantages of this is that you are able to operate your contraptions from some distance away as I don’t trust my ageing brain for safety with high voltages.In my case I also have a pacemaker fitted which is another can of undefined worms .Keeping the noise generated from high current high voltage switching is also nice to have, knowing that any induced noise is in one place and can be dealt with a lot easier than chasing ground loops where everything contributes as an antenna.Having complex switching circuits with the inherent noise and human mistakes on your well lit, well equipped bench is importantin my case as with others I assume.Making 3 phase motor controllers is another application where isolation makes things very friendly. It would not be hard to use this same method in reverse for feedback although I have not tackled this yet.I hope that this will make experimenting easier and safer for most who are rightly over cautious about high voltage to the degree that prevents their progress as there is no fallback position from high current dc passing through your body.