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| Floating probe! For $2.50 |
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| Yansi:
HCNR200 is well under $4 as far as I can tell. (Mouser, TME) If you go for speed, then don't 4N35. It is a "standard slow" coupler if I remember correctly. Any photo-transistor coupler will be likely very very slow with low collector currents. //What kind of distributors are there in Argentina? |
| JS:
--- Quote from: Yansi on September 11, 2018, 10:11:00 am ---HCNR200 is well under $4 as far as I can tell. (Mouser, TME) If you go for speed, then don't 4N35. It is a "standard slow" coupler if I remember correctly. Any photo-transistor coupler will be likely very very slow with low collector currents. //What kind of distributors are there in Argentina? --- End quote --- 4N36 was what I had in the bin. The kind of distributors we have here are mainly the old man who used to repair TVs so they know eventeverithing about vertical deflection but very little about any modern-ish components. Then you have the bigger stores which probably have the same old man in the desk behind the scenes and a bunch of kids dealing with the public, then you have some individual selling dedicated components for 20x what it should cost and some major importer that will get you anything you want for 10x what it costs but within the month (or two). In my city only the first two options, and 300km from here, in Buenos Aires, all of the mentioned flavors. When I was building guitar pedals and tube amps everithing was great, find an old man in a slow day or a kid like me interested I what I was doing and they would allow me to go into the pile of junk searching for all the good NOS they had... JRC4558DD, TA7136P, NE3101, silver mia caps, a wide variety of germanium devices, etc. With all that, any serious development here gets really frustrating pretty fast and working on my own becomes a thing about what can I do with the components I can find knowing it will be pretty easy with modern components. Building small gadgets to sell as a kickstarter seems like a very distant future seen from here, so to calm my thist of development I run into this projects useful for the beginers to help them in tooling their lab. For a day job I do industrial automation where all this is not usually a problem and I can work more freely. JS |
| StillTrying:
Using 2 optos in push-pull instead of any feedback :D, and using just the photo diode part, I can get the BW well over 1MHz. At least in the simulation it's linear with IN between +/- 2V @ +/- 10mA, OUT is unfortunately +/- 18uA, +/- 80mV. |
| JS:
Thanks for that, I'll try it in the breadboard! Did you observed the propagation dekay? JS |
| StillTrying:
"Did you observed the propagation delay?" I think it depends on how you define it. If I put a 1us wide 1.5V pulse through the sim it comes out looking like that, the half signal height delay is 120ns. There some real 1us pulses through red, green and white 5mm LEDs viewed by a photo diode here.- the last image. https://www.eevblog.com/forum/chat/20w-halogen-bulb-viewed-by-a-photodiode/msg1751210/#msg1751210 I still don't know why the light shape(and current) through a red LED is so curved for the first ~0.5us, I suspect IR LEDs might be similar, but not tried one yet. "I'll try it in the breadboard!" In the sim the current through the LEDs side is about 6mA, +/-5mA on the signal peaks, and on the photodiodes side about 7uA +/- 6uA, good luck! |
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