Till I got the needed capacitors, I continued to work on other parts of the project. 

The instrument need some way to display the actual voltage and perhaps the actual current consumption. 

Ebay has tons of similar products for it, from simple 8 digits to fancy oled types.

Another way would be to use an arduino and an lcd display to measure and show it. Because I happened to have an LCD display around, and also recently buyed an i2c interface for it I went this way. I hope to learn more of it.

Read about how to use an i2c interfaced lcd display with an arduino:

https://arduino-info.wikispaces.com/LCD-Blue-I2C