Opto-Coupler Tester

[Brett]

I'm confused now, which is not an unusual state of mind down here. This is the snippet of my schematic I used, do I need to flip the jfet upside down to be correct or what am I missing?

I’m probably the one that’s confused. @Chuck D. Bones, do you mind confirming which net TR1’s test point should be on?

 

[Chuck D. Bones]

Stephan has TP1 in the right place, on the JFET's gate and the end of the LDR that isn't grounded.

The Vactec is supposed to go in the ZIF socket, not on the board. You may want to change the way the Vactec is oriented in the ZIF socket.

 

[Brett]

Stephan has TP1 in the right place, on the JFET's gate and the end of the LDR that isn't grounded.

The Vactec is supposed to go in the ZIF socket, not on the board. You may want to change the way the Vactec is oriented in the ZIF socket.

This is the same point that we should be adjusting TR1 for 5uA as well?

 

[Chuck D. Bones]

Yup. Just install a 1M resistor in the ZIF socket where the LDR would go. Power it up and adjust the trimmer for +5V on TP1.

 

[cooder]

Cheers, the Vactrol or LED LDr combo can go on my layout either in the ZIF socket OR into the LDR/LED with push in sockets if that makes sense, both are parrallel. Basically to choose what ever fits best.
I guess with orientation of Vactrol in ZIF socket you mean length wise in there, I'll change that to it.

 

[cooder]

Here's the updated version with lengthwise orientation of Vactrol or LDR/LED in ZIF socket, I also threw in two more ground pads because I felt generous as usual.
Howzat?

 

[Chuck D. Bones]

Looks good.

I'll wire GND & TP1 to banana jacks.

 

[cooder]

Could we add a say four position rotary to this to scale the sensitivity of the LED blinking?
Like for GL5516, which have a lower dark resistance, have a switch position that makes the "cut off" point 10 k or 100 k?
Have four "cut off' points on a switch like 10k/100/k/470k/1M? That would allow to quickly test LDRs at different working points for what recovery rhythm they have and so match them not only for one measure point but for several.
Does this make sense and what part of circuit would we make adjustable/switchable? Would that be R 1 and R3?
Am I barking up the wrong tree with this whole idea?

 

[Chuck D. Bones]

All doable. Let me think on it and get back to you.

 

[Chuck D. Bones]

To change the dark resistance threshold, we just change the test current flowing thru the JFET. We do that by using a switch to select between different trimpots. The oscillator's trigger threshold is 5V. For a 1MΩ threshold, we want the test current to be 5μA. For a 100KΩ threshold, we want the test current to be 50μA. For a 10KΩ threshold, we want the test current to be 500μA.

Simple, eh?

 

[cooder]

Top notch! Cheers @Chuck D. Bones

 

[cooder]

I have just put this together and I can't get it quite calibrated to %v when I have the 1M resistor inserted into LDR test spots. I get it to 7.8 V, do I need another jfet with different Vp / Idss?

And while I'm at it, I have installed rotary switch with four trim pots, to adjust those to 470k/100k/10k thresholds do I need to insert an 470k/100k/10k resistor and measure again for 5V to calibrate or am I just confused as per usual?

Edit: I might add that it seems to work, I inserted a test vactrol and the white indicator LED blinks on the according switch setting, is off in middle position and light in other switch position.

 

[Chuck D. Bones]

You're saying it won't go lower than 7.8V with a 1M test resistor? If so, try a different JFET. A J201 with Idss > 500μA would be a good choice. Low Idss & Vp are preferable since we're trying to dial the drain current down to 5μA (5V across 1MΩ). Idss must be higher than the highest current at which you want the JFET to regulate. You could also try a larger trimpot for the 5μA switch position.

You will need 4 trimpots because we can only guess at the resistance necessary to make the JFET regulate at each desired current.

That's what the switch is supposed to do. LED held on lets us measure light resistance. LED held off lets us measure the dark resistance. Blinking LED is a quick indication of LDR health and response time.

 

[cooder]

Yes correct and I'll try a J201 will measure the Vp and Idss first, cheers.
Yes I tacked four multi turn trimmer onto mini 4 way rotary, not pretty but it works, will post photos for a bit of light entertainment once I have it all going.
Yes I got that with the toggle switch and works as wanted, so that's cool.
Again: if I want to calibrate it to 470k/100k/10k thresholds do I need to insert an 470k/100k/10k resistor and measure again for 5V to calibrate each switch position to that I suppose?
Thanks!

 

[Chuck D. Bones]

Yes, that calibration method will work. Don't try setting the threshold below 10K or the J201 might run out of steam.

 

[cooder]

Here's my effort then, and it works as prescribed.
I selected a J201 with Vp 1.103 and Idss 840uA ( long live the jfet tester... don't ya love it as well, I do, that I'm now into jfet testing and can throw measurements at ya @Chuck D. Bones haha...).
The trimpot for 1Meg threshold needed and extra 100k resistor tacked onto it to make it effectively 100to 200k range, then that calibrated nicely to 5V. The other switch settings do as I aimed for 470k/100k/10k threshold. The calibration particularly for the 10 k but also 100k was very touchy, so I was glad I had multi turn trimmers which really is the way to go here me thinks.
Also, I do find the four step indication of responsiveness a useful thing as it gives an indication of how lively the LDR / vactrol is and and how to match a set that is similar to some extent. Probably not super scientific but better than looking at them and not knowing.

The cobbled together rotary with trimmers tacked on won't score high in the elegance department, but it works and having a cobbled together utility box from a miss-drilled enclosure is fine by me. I even used an outie 9V jack to make it super bogan, ha.

And lid on, I also did a light screen on the white indicator LED to make sure it doesn't get any interference.

Bingo.

 

[Chuck D. Bones]

"All the light we cannot see."

We're watching that this week.

Nice job!

 

[cooder]

Yeah, we're watching that too...

 

[Kroars]

Great thread! You folks are awesome!!

 

[steviejr92]

Here's my effort then, and it works as prescribed.
I selected a J201 with Vp 1.103 and Idss 840uA ( long live the jfet tester... don't ya love it as well, I do, that I'm now into jfet testing and can throw measurements at ya @Chuck D. Bones haha...).
The trimpot for 1Meg threshold needed and extra 100k resistor tacked onto it to make it effectively 100to 200k range, then that calibrated nicely to 5V. The other switch settings do as I aimed for 470k/100k/10k threshold. The calibration particularly for the 10 k but also 100k was very touchy, so I was glad I had multi turn trimmers which really is the way to go here me thinks.
Also, I do find the four step indication of responsiveness a useful thing as it gives an indication of how lively the LDR / vactrol is and and how to match a set that is similar to some extent. Probably not super scientific but better than looking at them and not knowing.

The cobbled together rotary with trimmers tacked on won't score high in the elegance department, but it works and having a cobbled together utility box from a miss-drilled enclosure is fine by me. I even used an outie 9V jack to make it super bogan, ha.

And lid on, I also did a light screen on the white indicator LED to make sure it doesn't get any interference.

Bingo.

@cooder you have to be one of my favorite builders hands down….

Your execution is on another level