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RS Pro Digital Oscilloscope Competition Entry: Arduino controlled power supply

How it started...

I somehow like building and tuning benchtop power supplies. (I know, it's kinda strange, but it is how it is!) I have some standalone power supplies with linear regulation and regular turn knobs. However, with my interest in Arduinos and Raspberries, I wanted to connect these two interests together. And what was the result? An Arduino driven power supply, that will be controllable either directly using a rotary encoder or remotely from a computer connected through USB. I also wanted to make use of big B/W OLED display, that would be contrast and easily readable.

Original idea

My intention was to build a compact power supply, where the AC/DC part will be regular single voltage switching power supply. And the controlled part will be an externally controllable DC-DC buck/boost converter. I found a module "WD2002SJ" which is buck-boost configuration DC-DC converter that is controlled by three potentiometers - voltage, current limit and voltage cutoff. For my purposes, only the first two were relevant. The idea was to remove potentiometers and replace them by I2C digital pots driven from Arduino.

The showstoppers

During the building of the controller part, I found out that the regulating pots (voltage specifically) have output voltage on their pins. Which is not under specs of regular I2C digital pot - usually they have a limit of Vcc on their wire ends. So, having 5V as the supply voltage for digipot makes the ceiling of regulation of output voltage to... 5V, which is not acceptable for me. 

Another problem was with value and precision of the digital pots. I needed to find 500kOhm pot which will have enough steps to be able to regulate with enough precise steps. When thinking about 0-30V range and 128 steps of digipot, we get just 0.23V per step, which might not be precise enough for every application. 

What now?

One of the possible ways is to reverse-engineer my DC-DC controller board and try to make more in-depth customizations of the module, so I can regulate it, for example, using PWM from Arduino. Another way was to use another externally-controllable power supply module, but reverse-engineering will still come in place. So this will be exactly the point I will make use of the RS Pro Digital Oscilloscope. Measuring the output ripple and other parameters of the power supply will definitely be another good task for the scope. I am also interested in vintage computers, especially 8bit Commodores. I also repair them and an oscilloscope will really come to hand in this field, too!

BTW., I loved the idea of "A compact and portable tabletop maker space for homes" here on DesignSpark. We have quite a small flat, so any space-saving ideas for tinkering in a living room are always welcome!

I am a hobbyist - tinkerer - fan of everything techy. I always wanted to know and try everything on the world and find out how it works. But it is obviously not possible, so I at least try to achieve that... :)

21 Jun 2018, 12:50