Digital Volt-Amp Panel Meter for power supply

Short requirements

I have bought a server power supply 50V 1200W and made voltage and current adjustable. And now I need a display to show output voltage and current.

Yes, it is much easier to buy the voltmeter on the market, but more fun to do it yourself.

The requirements:

• 5.. 60 V measured voltage
• 30 A max current
• when the potentiometer for the current limit is changing - show the max current value, not measured
• Two separate indicators for the voltage and current
• the power supply already amplifies the value of the current, so no shunt resistor and amplifier is needed, simple measure OpAmp out voltage

Teardown

This is the voltmeter that I bought on the market. It has a shunt resistor and amplifier for the current measuring. The parameters are something like 100V 10A max.

The prototype

I am gonna use a common cathode 7-segment LED display.

So, I need 8 digital outputs to drive A..G, and DP inputs and 6 digital outputs to choose which indicator I want to drive (14 digital pins in general). It is called Dynamic Lightning Method, so I don't need 54 pins to control six 7-seg indicators.

To measure voltage, current, and potentiometer I need 3 ADC channels.

I soldered two displays and potentiometers on the universal PCB board for prototyping.

The second step is to read the Documentation, for the SoC and Dev Kit that I am going to use:

• DA14585 SoC link
• DA14585 Development Kit link

I have a DA14585 in the QFN48 package, so it has 48 pins in general, which is enough for me.

The software for this SoC :

• µVision IDE - Keil (to write and compile the code)
• SmartSnippets™ Toolbox (to program SoC)

DIY PCB

I wanted to check if the schematic and SoC settings are correct, so I made a PCB. I've used hydrogen peroxide, citric acid, and kitchen salt for etching. It is transparent liquid at the start, and becomes green during the etching, looks very cool!

It is a little burned out, the temperature during soldering was too high for the PCB, but the SoC has started so I can place an order for the JLCPCB.

Final PCB

Two weeks and I have my white manufactured PCB

After some soldering (this time the temperature is correct, no burnout) it is ready for programming and testing

But I run into a problem - the power supply measures current on the positive terminal of the output, so I'll have to measure negative voltages. The schematic is very simple. There is one thing to take into account - the voltage will be inverted.

• 0V power supply - 3.3V ADC
• 60V power supply - 0V ADC

So, I had to cut some wires on the dividers and add wire to the 3.3V MCU VCC

After some measuring and tuning of ADC coefficients in the software, everything works well.

Next to do

The next step will be to get rid of the russian labels, repaint the front panel, add a switch to turn off the output and print a hole cover.