seems to remove ambient light and not allow the opamps to saturate

I used an HP pin diode in the receiver of my, (our, my partner and my) long-range, (6 miles) free-air Hi-Fi laser communications system. It used a $1 three mW red laser pointer transmitter. The whole thing cost about $30 for a 6 mile range, but I'm going to do this balancing mod to improve it's range even further though I'll speed up the time constant for my outdoor application. I do love lasers.

I made something like that decades ago for a light pen, which would allow a signal to pass while cancelling the varying ambient light.

Loving your videos. Just pure technical stuff. You should have 500K subs and Dave should have 30K comparing yours to his recent content.

Very cool circuit! This gave me some good design idas to try! Thanks for posting!

It reminds me of the pickup amplifiers in a CD player. They need to measure the peaks and lands of the disk but need to servo out any disk warp. The amplifier needs to have a nearly DC response but also a DC offset reject for any warping.

Oh My Goodness I need one of those pin straighteners that you mentioned! I am doing work on ancient LM741 opamps in those stupid 8 pin metal cans. Inserting them into sockets can be a real pain in the butt. It never occurred to me to make something like that. I'm going to tell my boss about this tomorrow and see if we can get something made.

WoW it's super well thought out, I wouldn't have thought of it, it will have great stability, the mutual ratio can be fine-tuned with a trimmer, WoW thanks for the video, very informative. Nice day 🙂 Tom

I can suggest an application for that. Patch the output into an audio amplifier then aim the sensor at a faucet dripping into a saucer and see what it sounds like. Then, with a focusing lens, aim it at the sky on a rainy day. In fact aim it, possibly via a small telescope, at anything in nature. That is what my inventor friend in Canada called an Audiolumitron. His sensor was a solar cell using a small lens one might use for reading fine print. If you examine a histogram/spectrogram of the sound produced you will realize a big difference between snowfall and rain, and clouds that are generating precipitation that hasn't reached the ground and those that have. I'm curious to know of a photo diode will respond the same as a photocell to organic stimulus.

I have an instrument grade photodiode which I picked up as a curiosity, but it's not quite as big as that one- it also happens to be Bulgarian.

Possibly the slow gain control is there to mimic the response of the human eye to large changes in the amount of light. It can take our eyes several minutes to adjust to large changes.

My guess is 1uf is actually 1ut for 1 microsecond time constant filter.

Measure the uF of your PIN diode. For wide-area PD those can be fairly large (but perhaps not as large as 1uF, unless it's not PIN photodiode. Maybe they mis-read 1.0 nF, 1000pF? Decades ago the "nF" was still in use.) Also, connect the P.D. to -15 not to gnd, to speed it up. Also, WHICH OP AMP? or did I miss it? Not labeled on schematic. Decades ago, some of the quality expensive op amps were still only available in TO-5 cans. Or was this far earlier, uA709 etc.?

HP was famous for pounding round pegs into square holes...

I use mosfet ( 2N7000 or BS170 ) as a source follower and photodiode conected between drain and gate. PIN photodiode anod to gate.

That was fun.

Couldn't you just simply send the amplified signal to second opamp and use it as a high pass filter?

hey I have 4 or 5 bournes 10 turn knobpots (100kOhms) that I got from a scrap box I bought at the MIT flea. What kind of op-amp circuits should I build around them?

What was this part used in / or? My guess is a scintillation counter for samples to emit photons at a specific frequency for counting [common in biology labs].

BTW what's a y bar detector? I remember a photomultiplayer was used to amplify the lights and signals before opamps eara.

nice Video - you mentioned MicroCap - you know by any chance how to send MicroCap schematic to KICAD? or just the netlist?

Fast scurrying creature(s) detector with ambient IR illumination/background compensation ???

What type of opamp was used here?

I have some of those round op amps, I don't know the pinouts

Why the 100k feedback for the follower?

cool

Why don't you just solve it mathematically? Write out some node equations and reduce everything to H(s), eg; Vout/Idiode? I think the second opamp is to null out dark current.