InGaAs avalanche photodiode receivers on eBay

Jim Thompson wrote:

Of course you'd need an isolated power supply to be able to apply feedback to the optocoupler...those aren't the same as a dual matched opto, where you can invert the transfer curve on the LV side using an op amp.

I'd be inclined to put the PUT device inside a bridge rectifier made from two optos and two diodes, so you can get the polarity and the current as well. (That's a variant of Pease's trick with the voltage reference inside the bridge rectifier.) If you're brave you can save one photocoupler, but I'd prefer to subtract the two photocurrents on the left side to get a more reliable polarity indication.

I_IN | *--------------------------------------------------* | | / --- --- LED |/ / \\ \\ / --> | photo --- --- --> |v | | \\ | | | | | | | | (Subtract to | *-------------------------------------* get polarity) | | | | | | | | Rprog | | *----------* *------RRRR--Vprog | / | | |/ --- LED |/ | | --- 2N6028 / \\ --> | photo | --- \\ / PUT --- --> |v | --- --- | \\ | | | | | | R | | | R | | | R | | | | | | | | / | | | --- LED |/ | | | \\ / --> | photo | | | --- --> |v | | | | \\ | | | | | *------------*----------* (Magnitude) | | | | | --- | \\ / | --- | | | | | | | *--------------------------------------------------* | | COM

Cheers

Phil Hobbs

I ordered 20 HCNR200's ;-) ...Jim Thompson

I'll probably get a few too, just to have lying around. Where are you going to get the power for the floating linearizer?

Cheers

Phil Hobbs

Not. I going to parallel the PD's, use two HCNR200's in the fashion as in URL I posted. I only need polarity information.

This is for my 800-number killer ;-) ...Jim Thompson

Digikey also carries them. But again, this was only one example, you don't have to the expensive hi-iso stuff unless needed.

Cheapest way is usually a LAN or DSL transformer. In a pinch that could be hacked out of a hub where the power supply died. As sad as it is: Once I bought a brand-new 4-port from a store for five bucks and unsoldered the transformers. Better than buying at $3/pop plus S&H, and waiting for Fedex to come. Plus I had a nice "night-blue" aluminum project box and a slim-line wall wart for free.

If you need ultra-low capacitance or hi-iso without the teflon wire, two pot core halves in a series resonant scheme work nicely. You can even get power through a dual-pane window that way :-)

I thought you needed to actually measure the current.

Cheers

Phil Hobbs

Neeerp! Just polarity. Can't tip my hand right now, but I'm working a way to get caller-ID without ringing phones inside the house, making decisions, allowing ring, dis-allowing rings... roll to VM, or nasty kill ;-) ...Jim Thompson

Speaking of opto oldies....

Somebody doesn't put part numbers on his pencil-sketched devices. This might be a whine, if I thought that John Larkin had real parts in mind when he scribbled his sketches. No doubt he relies on his subordinates to fill in the petty details, so it is more of a cluck.

Nah, they just aren't as cute as that floating-Murata-tile gate driver. ;)

(I was mining some old SED stuff for possible inclusion in the new book, and hit ctl-R instead of ctl-L.)

Cheers

Phil Hobbs

GaN is amazing. Circuits that look obviously amateurish and stupid just work!

I did seem like an oldie, but that's not bad.

At least it was on-topic!

Now that olduse.net has shut down--it was fun while it lasted--we should maybe bring back an old thread occasionally. The Hills and Woodgates and Schulze-Clewings and Wescotts and Willamses and AESes and even Thompsons and Misos of yore had some good things to contribute. (We don't have to rescuscitate the Eeyores and Roberts and Uncle Als.)

Cheers

Phil Hobbs

I'd add Genome / DNA to that list.

indeed. I also gave credence to John Fields Rich Grise

James Arthur Kevin A & Spehro - could up their quotas ;-)

I cant complain, no time to do much real design work... once I retire though, I have a pile of ideas waiting for me

Which one? ;)

Fields occasionally had good things to say, but the interminable JT/JL/AWS flame wars were much, much worse when he got involved.

Cheers

Phil Hobbs

Most of my interaction with JT was technical. He liked to insult people.

I suspect he drank himself to death. He talked about wine all the time and got pancreatic cancer.