I'd found an antique gauge on Ebay, the same type used in RAF Lancaster bombers, spitfires and several other aircraft. This particular one was used in a Lancaster and dating from 1943. I wanted to be able to drive the gauge using an Arduino, the idea being that I could use it to display system temperatures.
Step 1: Disassembly: Bezel
The entire outer casing for the gauge is made from Bakelite and has that distinct old electronics smell. The red front bezel easily was a little tough to remove the first time, but after that a tiny amount of grease was added to the thread to make future maintenance easy.
Step 2: Disassembly: Remove Mechanism
Carefully remove the three small brass screws from the back. This will allow the mechanism to come free of the casing.
Step 3: Admire
The brass mechanism inside is really a thing of beauty. The tiny hand soldered parts and the lovely cast brass and tiny gears are so pretty.
Step 4: Disassembly: Remove Hand
With extreme care not to scratch the face remove the hand from the front of the dial. You can get specialized jewelers tools to do this, but a small screwdriver works ok if it is not too tightly pressed on.
Step 5: Disassembly: Remove Face
With the same extreme care not to scratch anything take the two even smaller brass screws out and the face comes off.
Step 6: Collect New Materials
This project uses the switec X27.589 stepper motors to drive the hand and an arduino nano to run.
The X27 X25 stepper motors are ideal for this project, they are cheap, small and there is allready a really good library made by Guy Carpenter: Using the SwitecX25 Library The library really makes controlling the motors easy.
Step 7: Construct New Internal Mechanism
There are a few pre-made breakout boards for these motors but sadly they were too small to fit inside this little gauge. So I simply constructed my own using strip board, using a hole saw to cut to size. This board makes the front half of the mechanism.
The back plate was cut from 3mm MDF using the same hole saw. This will allow the entire thing to be mounted using the same screw holes that the original mechanism used. The nuts for these screws were carefully glued to the MDF using some epoxy resin.
The motor and its wires soldered to the strip board and the front and back half's separated using some long bolts.
Step 8: Mounting the Face
After a quick paint job, not really necessary but it does improve the aesthetics when you take it apart it was time to mount the face.
I wanted this project to be reversible, I didn't want to use glue or anything that would require drilling into the gauge. So blue tack was used and as its indented to be a static object it should be strong enough to hold it in place. A small bit of tack shown in the photos was also added to the back to hold it more firmly in place.
The arduino can then be soldered into place, putting diodes between its digital pins and the motor, along with an lm35dz temperature diode.
Step 9: Mounting the Hand
Amazingly the tiny hole in the hand was the correct size to fit nicely onto the X27 motor shaft without any modification.
Step 10: Upload Code
These two examples are very simple.
One uses the data from the lm35dz sensor to drive the gauge with some modification as the gauge only goes up to 24. I'm still debating how I want this to work, but at present you simply add 20 to whatever the gauge says. So 8 on the gauge will equal 28 degrees.
Other example runs the gauge forwards and back to demonstrate the movement.
You will need to have the Switec X25 library installed.
Step 11: Finish
I still need to mount it into the front of the PC, I'm still debating where I want it exactly to go.
Thank you for reading my first Instructable :)