[SOLVED] program to control a virtual resistor

[wayne_]

I want to use some form of controller [program] to vary the resistance of a resistor which is physical or even virtual;

The resistance is one that changes from a fixed large base resistor of 150 M Ohm down to 1.5 M Ohm less then after 12 hours up to + 151.5 M Ohms
I have had advice that a LM13700 transconductance amplifier may make a virtual resistor.

It does a good job... I can use a small 10 to 100 Ohm variable R as a control.

I need to automate however during a specified time of 24 hours the increment and decrement of that resistance.
[The small virtual 10 -100 Ohm controlling resistance].

Any one suggesting some creative answer?

 

[BradtheRad]

A light dependent resistor (or CdS photosensor) will do what you want.

Since you mention a program, it suggests you have a microcontroller. It will keep time. It has an output terminal which will produce a voltage you can adjust via programming.

Send that voltage to an led (through a safety resistor). The led shines on the LDR. Vary the led brightness so that it causes 10 to 100 ohms resistance in the LDR.

If it won't go as low as 10 ohms, then connect a few of them in parallel.

 

[wayne_]

Really a CLeVeR solution...

I am considering learning to program a PIC chip... FROM HERE:

http://www.talkingelectronics.com/html/PIC-Page01.html

It seems daunting as I had last attended ABQ. TV-I tech/vocational Inst. in '90.
Had basic machine lang. then been awhile.

Will any computer interface be OK in the meantime you suppose...?

Again great idea!

 

[BradtheRad]

Will any computer interface be OK in the meantime you suppose...?

Whatever you use needs to be able to produce a variable voltage, either:

* from one pin (analog),

* or from several pins (e.g., microcontroller, parallel port), through a digital-to-analog converter,

* or by variable pulse-width (USB port), through an averaging and smoothing RC network.

Any of these will be difficult with a modern-day computer. The audio output may be a possibility, if you can create the right waveforms at the right amplitude. You may need to amplify it as well.

 

[wayne_]

This AU website has tutorials of the PIC chip

http://www.talkingelectronics.com/html/PIC-Page01.html

The new version does counting sequences [chip and programmer]

Appreciate the attention on all of it1