A simple adjustable constant current dummy load, with digital readout and USB data logging.
Inspired by the dummy load made by Dave from the EEVBlog. I decided I wanted one because I work with a lot of battery powered designs and it’d be nice to have a simple way of testing a battery or power supply in terms of capability, capacity, and heat. It features a 2 line voltage and current reading, a rotary encoder as the user input to adjust the current setting, and USB data logging (plus bootloading). There are more neat features, please watch the video.
Here are some pretty pictures: (Imgur Album)
Tech Details: ATmega32U4 as the main microcontroller, a dual channel 16 bit ADC for measurements and a 12 bit DAC to set the current. The current limit right now is about 1.5 amps.
All the files are hosted on github, https://github.com/frank26080115/DummyLoad. The “readme” there has some instructions, calibration steps, and the serial terminal commands.
After a lot of testing, I realized the circuit isn’t the best. The DAC’s output voltage is too low and right now the current is limited to 1.5 amps because of this fact. Also, in comparison to true labratory equipment, the accuracy of my device is untrustworthy by comparison. I do not recommend you trying to rebuild this project using my current design.
The DAC’s output can be boosted by turning one of the voltage follower OPAMP circuits into a non-inverting amplifier, done by adding two resistors. The accuracy problem can be resolved by a more complex calibration process.
More details coming later.