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|19th March 2019, 06:30 PM||#1|
Join Date: Aug 2004
Location: Behind you
DC Electronic Load controlled by a Raspberry Pi
This isn't directly audio related, but it has some indirect uses, such as testing power supplies, so it might be of interest to some people here. It's a Raspberry Pi-based DC electronic load. I built it because I wanted one with a nice graphical display that I could control with any device over WiFi, and such a thing does not appear to be available commercially.
The electronics are simple. Basically it's just this:
Which is one op-amp with current feedback and one with voltage feedback, both sharing an output transistor. The op-amps have a shutdown function which makes their output high impedance, so only the one enabled op-amp controls the output transistor at any given time. The voltage feedback is not connected to the load in the schematic, it is instead connected directly to the input connectors, to minimize the effect of the resistance of the wiring. Additionally, it can be switched to a second pair of connectors, so it can be wired up to sense voltage remotely.
There is also a DAC and an ADC to let the Pi control the load, and read current/voltage back from it, and some voltage regulators, as it runs from a 12V wall wart, while everything inside needs 5V.
Here's a photo of it working, displaying a measurement of the total energy it just drained from a supercapacitor, which allows capacitance to be calculated (standard capacitance meters can't cope with capacitors of hundreds of farads).
I managed to find a case which was close to the perfect size for the touchscreen on the front, the connectors on the top, and a big heatsink on the back.
And lastly a screenshot of the GUI as it appears when run on a web browser on a PC, demonstrating how the load can be scripted to do things like ramp the current up and down.
It's capable of 10A, 50V and 100W. It can take over 100 samples per second, though it gets a bit noisy as the sample rate increases. There is a longer description and full source code on my website.
p.s. It would be nice if the forum allowed SVG images, as that's a better format for schematics than bitmap images.
Last edited by Mr Evil; 19th March 2019 at 06:33 PM.
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