I built a regulated power supply using a lm317 regulator. I put it in a plastic box and added 2 pairs of banana plugs, one pair for the volt meter and one pair for the device. Getting tired of hooking a meter up to the box each time I wanted to use it, I decided to incorporate a digital meter in the box. I was at Harbor Freight and saw a digital meter for less than 5 bucks and decided to use it. Since I am only using it for volts less than 20, I decided to gut the meter, hardwire the contact points in the rotor switch for 20 volts, and put it in the enclosure. When I took the back off, I noticed there is a 2 inch silver square on the back that is connected to the circuit board by a spring similar to a ball point pen. I assume this is a ground plane. Is there way that I can substitute something else for the ground plane? Could I solder a piece of aluminum can to a piece of wire and have the same thing? What would the easiest way to emulate this silver plate?

Thanks

 

Most digital meters cannot measure the voltage that they are powered from.

 

That would be why I am gong to keep the 9 volt battery intact with the meter.