Infrared Potentiometer in PT2399 delay

[pecfor]

Hi Guys,

this is the first time I put a new topic on. I've a simple idea but I don't know how to get started with it.

I'd like to modify a PT2399 delay swapping the time and feedback pot with infrared sensors. I've noticed that normally the IR sensor give a variable voltage in output. How can I substitute a standard pot (with is a variable resistance) with a IR sensor without messing up the circuit?

In the PT2399 for example, pin 6 is normally connected to a 20K pot in order to vary the time repetitions. If I'd want to remove the pot and put an IR sensor there, how should I change the circuit?

Thanks a lot!

[pecfor]

Anyone?!?!?!

[Nocentelli]

I imagine you would need to send the voltage output from the IR sensor to an op amp or transistor, using the voltage to control the output of the amplifier to drive an LED, and use the LED's brightness to control the resistance to ground of the delay pin via an LDR. You might need to invert the response of the amplifier if you wanted more IR~>longer delay.

I typed "IR sensor to resistance" into Google, and the second result:

https://www.google.co.uk/url?sa=t&sourc ... -ZBr_MzVeg

Shows how an IR sensor can be set up to output a scale-able voltage (presumably could act as a sensitivity pot).

I'm interested in how you plan to use this - Perhaps you could use an LDR instead, and control the delay directly with visible light rather than use IR and a string of associated circuitry?

[~arph]

Why IR? I believe IR sensors are usually photo diodes/transistors and therefore are more suited to act as a logic switch rather than a variable resistance. I'm not saying it can't be done, but it would require additional circuitry to get it to replace a pot. also note that if the pot is not wired as a variable resistor (only two lugs used ) you need a more complicated circuit.

Edit: nocentelli posted at the same time as me, here is my comment anyway

[grrrunge]

I've recently built a line sensor for use with robotics, that utilizes IR LED's and IR photodiodes. It's simple and less prone to pick up noise from the ambient light around the sensor circuit than solutions using LED's and LDR's.
IR photodiodes put out small currents, so you'll want to build a transimpedance amplifier, that'll convert the current from your photodiode to a DC voltage. With that DC voltage, you can then control some sort of voltage controlled resistor circuit.
It should be possible to build the entire circuit around two MOSFET's

[grrrunge]

These two links might interest you:
http://www.vishay.com/docs/70598/70598.pdf
http://www.linear.com/solutions/Transim ... Amplifiers

[pecfor]

I

I'm interested in how you plan to use this - Perhaps you could use an LDR instead, and control the delay directly with visible light rather than use IR and a string of associated circuitry?

Hi! thanks for your precious advice! I think using only the LDR would be a problem because it could be affected by the different lightning conditions in the room? with the IR calibrated for a short range I might be able to control precisely the variation of the time with my hand.

I found this: http://revolutiondeux.blogspot.co.uk/20 ... oller.html

I think I could use the same circuit with a IR instead of the antenna?

[pecfor]

also note that if the pot is not wired as a variable resistor (only two lugs used ) you need a more complicated circuit.

Hi! interesting... Yeah I didn't considered the other option... Could you give me an advice in case of the pot is not a variable resistor? I guess I should play with the circuit before the optocoupler... Thanks a lot guys!

[Nocentelli]

Most PT2399 delays I've seen just need a single variable resistance between pin 6 and ground.

[pecfor]

Most PT2399 delays I've seen just need a single variable resistance between pin 6 and ground.

Ues you're right but I was planning to modify also the feedback pot (repeats)... And that one looks like a problem to me!

[~arph]

also note that if the pot is not wired as a variable resistor (only two lugs used ) you need a more complicated circuit.

Hi! interesting... Yeah I didn't considered the other option... Could you give me an advice in case of the pot is not a variable resistor? I guess I should play with the circuit before the optocoupler... Thanks a lot guys!

Well it totally deplends on how you intend to make the IR sensor output into a variable resistance. But the simple generic solution is to use two IR sensors and invert the output of one, so they both go in different directions. One causes a decrease of resistance then light enters it while the other causes an increase. This way you have both sides of the pot.

[pecfor]

Well it totally deplends on how you intend to make the IR sensor output into a variable resistance. But the simple generic solution is to use two IR sensors and invert the output of one, so they both go in different directions. One causes a decrease of resistance then light enters it while the other causes an increase. This way you have both sides of the pot.

totally right! thanks a lot!

[Dirk_Hendrik]

Most PT2399 delays I've seen just need a single variable resistance between pin 6 and ground.

What's needed in essence is a current control between 6 and ground. So what's needed is a IR to current controller.
The Yerasov schems seem lika an axcellent starting point again.