Clocked Variable voltage circuit

[Alex Margetts]

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

 

[Tunelabguy]

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.

 

[Alex Margetts]

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?

 

[Tunelabguy]

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.