Hi,
I'm trying to learn about PWM and at the same time possibly make a project that can create a 4-20 mA signal. I have basic knowledge but not too much into the specifics. I'm using a PIC 16F877A with mikroBasic on Easypic5 board using their example for PWM. When I tried this out I had the following results (with PWM set at all out).:
I connected my meter between RC2(PWM) and ground and read 5.02 volts. I thought this would be what I got so I was happy.
Then I connected a 220 Ohm resistor to RC2. Changed my meter setting to mA. I hooked my meter+ lead to the resistor and - lead to ground. I thought since 5V/220 Ohm is about 22mA that is what I would read. Instead I got about 17.1mA. I was curious, so I hooked another meter across the resistor to check the V drop. That read about 3.75V.
Any ideas? This has been driving me crazy all week.
I've attached my drawings, one for before resistor and one for after.
Thanks,
Ed
I'm trying to learn about PWM and at the same time possibly make a project that can create a 4-20 mA signal. I have basic knowledge but not too much into the specifics. I'm using a PIC 16F877A with mikroBasic on Easypic5 board using their example for PWM. When I tried this out I had the following results (with PWM set at all out).:
I connected my meter between RC2(PWM) and ground and read 5.02 volts. I thought this would be what I got so I was happy.
Then I connected a 220 Ohm resistor to RC2. Changed my meter setting to mA. I hooked my meter+ lead to the resistor and - lead to ground. I thought since 5V/220 Ohm is about 22mA that is what I would read. Instead I got about 17.1mA. I was curious, so I hooked another meter across the resistor to check the V drop. That read about 3.75V.
Any ideas? This has been driving me crazy all week.
I've attached my drawings, one for before resistor and one for after.
Thanks,
Ed
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