Power Supply Monitoring with Arduino
Recently I picked up an Arduino Pro (designed by the guys over at Sparkfun) in order to add temperature and current monitoring to my new Hurricane Power Supply. The Hurricane is designed around Ti Kan’s Sigma22 power supply module but includes a hefty 50VA shielded toroid as well as a secondary 5V power supply (Ti’s Sigma25) for secondary systems such as the Arduino and panel indicators.
The Arduino monitors the air temperature in the Spitfire amp as well as the power supply and displays the data on the LCD display. The colours got a little skewed in the video but in reality the display is a crisp white-on-black number with adjustable backlighting controlled by a PWM output on the Arduino*. The video below shows the boot sequence during which the board enumerates the connected sensors, performs a little calibration and then starts monitoring.
The Arduino also serves a second function though. On the front panel of the PSU are three LEDs that display power, fault and temperature statuses respectively. I picked RGB LEDs for this purpose so that I can experiment with different colour schemes but also so that the temperature light can be dual-purpose, displaying orange for a high temperature reading in one module and changing to red for high temperature in both amp and PSU enclosures. As a bonus this means that I also get full control over the panel indicator brightness with the possibility to enable some sort of “night mode” to dim the LEDs in darker environments.
Presently the data displayed on screen is just there to serve as an example but the Arduino is able to detect and communicate with two Dallas DS18B20 sensors on the 1-wire bus. These are digital sensors with 12 bits of resolution and should be accurate to within half a degree or so. One of these sensors is connected to the amplifier’s dB2 backplane board and communicates over the umbilical cable, the other is connected directly to the power supply’s PCB.
Meanwhile, current sensing duties are performed by Sparkfun’s ACS712 breakout board that can measure up to 5A of current. The Spitfire amplifier should draw about 600-700ma and the transformer has 2x 18V secondaries making 21.6 – 25.2W under normal operation.
Now to get the front panels machined and fit it all together…
* There was some discussion on the Sparkfun product page for the LCD module as to the correct resistance to use for contrast adjustment. I bought a 10K trimpot to experiment but I found that a spare 2.7K resistor did the job just fine with 4.7K being too faint and 600Ohm being totally washed out.
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