Hello,
Per John Caldwell suggestion I want to use a microcontroller PWM output with a low-pass filter as a D/A converter and trim the duty cycle of this PWM waveform to correct the offset in a wheatstone bridge. Can someone please provide the schematic for that circuit?
thank you
Igor,
Here is what I was suggesting in the other thread:
The schematic shows and INA333 but an INA122 would work as well. A resistor will still be required between the output of the low-pass filter and the bridge itself. The DC output of the lowpass filter will be approximately the duty cycle multiplied by the logic level high (e.g. 3.3V * 50% duty cycle = 1.65V). For accurate calculation of the trim voltage/duty cycle you will need to know the impedance of the elements in your bridge which can be determined by measuring the resistance from the supply to the ground pins. I should also note that the unusually high gain of your circuit shown in the previous thread will make trimming a challenge as even extremely small offset will cause large swings in the output voltage.
