This is my fist instructable and part of a bigger build. I wanted to document these steps for reference and for anyone to gather ideas.
I purchased this meter with the intent of building a mad scientist or Frankensteins lab prop. As the picture shows the glass is broken and there is no needle for the measured voltage. ( the one needle with the round bit on it is just an indicator).
Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.
Step 1: Inspect and Plan
I did find the coil still functions and only missing the needle. I epoxied on a new needle made from a piece of thin copper wire painted black, adjusted the counterweight and was able to make the meter move to full deflection with less then 1 volt. I added a resistor and an old volume control potentiometer and now can move the needle anywhere from 0 to 300 volts with just a 5 volt input.
Next Lights, The scale has some convenient mounting holes at the bottom, a perfect place to mount a board for the lights.
Step 2: An Unexpected Find
On removing the scale from the meter I found that this meter is much older then i had first thought. There is a handwritten order number and date on the back of the scale from 1925, very cool! wonder who H.R. was.
Mounted perf board with a couple screws and nuts to bottom of scale.
Step 3: Fit the Parts
Mock up of the warm white LED's. Used flattop LED's to have a wider beam angle. Also made sure that the components will clear the needle as it passes overhead
Step 4: Looks Good
Looks like the LED configuration will work well.
Step 5: Wiring Prep
The back of the meter looks like where all the connections and control resistors were and why this meter went to max deflection with less then 1 volt. The post left behind were a perfect fit for a couple of terminal blocks and they lined up really well with the holes to pass wire through. Used some modern hardware to attach the block to the meter and will use one block for the meter operation and the other for lights.
Step 6: Wiring Cont.
Soldered wires to the meter mechanism and to the light board. Crimped on some terminals and connected to the terminal blocks.
Step 7: Lets Give It a Go!!!
Looks great and runs on 5 volts or 3-AA batteries. The potentiometer (not shown) controls the meter deflection and can have the needle anywhere on the scale just by adjusting the potentiometer. The broken glass was replaced with acrylic as my glass working skills are next to none and much cheaper as I had the acrylic on hand as with all the other parts from this build, the only thing purchased was the meter itself and that was very affordable.