Clocked Variable voltage circuit

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Alex Margetts

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Hi all, i am fairly new to electronics and need some guidance.

I wish to create a circuit that reduces levels of output voltage fairly accurately ~0.01V over a set time period. The idea is that every 24hrs voltage levels will be fractionally reduced. Any ideas on how this can be done?

Also I have some experience programming microcontrollers in C

I appreciate your help guys!

Cheers,
Al
 

A 12-bit D/A converter is easy to get in a single chip that can interface with SPI to a microcontroller. 12 bits means you can control an output voltage from 5 volts down to 0 volts in steps of 1.2 mV, which is almost 10 times better resolution than you asked for.
 
Cheers Tunelabguy,

Do you think it would be possible to do this by controlling the duty cycle of PWM, If so this would only require a microcontroller?
 

You could do this with PWM, but realize that you are going to need a ton of low pass filtering to get down to the same accuracy level as a true D/A. For example, suppose you use 1 usec. increments on the duty cycle. To divide a 5 volt signal into 0.01v steps, you will need a period of 500 usec. To reduce the PWM ripple to only 0.01v with a 1-pole RC filter, you will need a time constant of 500 periods, or 1/4 second. Maybe for your application you don't mind waiting a few seconds for a voltage change. But that is the kind of slow-moving performance you will have to put up with.
 

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