I am making a lab power supply from a salvaged desktop supply and I would like to measure the actual voltage
and current from each supply. I am trying to get away with one small panel meter. The schematic is attached.
Please let me know if you see any problems with it. I am using a two wafer rotary switch.
Thanks

 

seems a strange way of doing things .... wouldn't it be helpful to see both current and voltage at the same time?? Another meter would only cost a few$... you don't indicate current levels , at high currents the resistance of the switch contacts could make readings inaccurate

 

Panel meters are expensive for some reason ~ $12 w/o shipping. I have a heathkit supply and it has one meter and you switch between current and voltage between 3 supplies, so I am modeling this one after that one. I just want to make sure i am not shorting things so I will normally have the meter in current mode when I turn something on. Current range only up to 5 amps and most of the time less than half that.

 

If you power the meter from the same supply it is measuring, you need to generate a negative voltage to it. Many meters will state in there specifications whether they are suitable for measuring their supply voltage.

 

To measure current you need a meter that needs only a very low voltage for full scale as that is the voltage you will lose from the supply voltage. It then follows that you will need series resistors for the voltage ranges which your diagram does not include.

 

To measure current you need a meter that needs only a very low voltage for full scale as that is the voltage you will lose from the supply voltage. It then follows that you will need series resistors for the voltage ranges which your diagram does not include.

Its been a while since I've read up on analog panel meters, LOL. Your right about the resistor in series for voltage that will need to be added. Now I am thinking about loading on my circuit by the meter. Geesh. Maybe a small micro with an A/D and an LCD would be better.

If you power the meter from the same supply it is measuring, you need to generate a negative voltage to it. Many meters will state in there specifications whether they are suitable for measuring their supply voltage.

I have not heard of generating a negative voltage to compensate for the meter, I will look into it.

 

Marlin P Jones Associates (https://www.mpja.com/) have a selection of panel meters. Here's just one example of a dual voltage/current meter:



https://www.mpja.com/Mini-Panel-Meter-Dual-LED-Display-30-Volts-10-Amps-DC/productinfo/30303+ME/

Note this in the specifications: "Input Range: Self Powered: 4.5-30V"

Any digital meter you get will require a minimum voltage to work. At least that one can be self powered (i.e., measure its supply). Of course, if you have an independent supply for the meter, then it can measure down to "zero."

 

Marlin P Jones Associates (https://www.mpja.com/) have a selection of panel meters. Here's just one example of a dual voltage/current meter:

https://www.mpja.com/Mini-Panel-Meter-Dual-LED-Display-30-Volts-10-Amps-DC/productinfo/30303+ME/

Note this in the specifications: "Input Range: Self Powered: 4.5-30V"
Any digital meter you get will require a minimum voltage to work. At least that one can be self powered (i.e., measure its supply). Of course, if you have an independent supply for the meter, then it can measure down to "zero."

That looks good. I am not looking for much accuracy just something to let me know the voltage is there and the current not trying to go through the roof. Thank you !

 

Marlin P Jones Associates (https://www.mpja.com/) have a selection of panel meters. Here's just one example of a dual voltage/current meter:

View attachment 166607

https://www.mpja.com/Mini-Panel-Meter-Dual-LED-Display-30-Volts-10-Amps-DC/productinfo/30303+ME/

Note this in the specifications: "Input Range: Self Powered: 4.5-30V"

Any digital meter you get will require a minimum voltage to work. At least that one can be self powered (i.e., measure its supply). Of course, if you have an independent supply for the meter, then it can measure down to "zero."

Also found on eBay for cheap.