Digital Caliper ON/OFF-Slide-Switch-Hack

One major drawback of most of the cheap digital calipers is, that the ON/OFF switch is not really a physical ON/OFF switch that cuts the power. Rather the switch is a means to disable the screen only. This results in a minimal but permanent power drain even when the caliper is not in use. Actually, it is never really “off”. The button cells get quickly exhausted therefore.

As of today, people have come up with various solutions for this issue:

Using a mechanical caliper again.
Taking out the battery after each use.
Using a foil to isolate the battery.
Instead of a foil, using the caliper’s data port to add a 3D printed isolation “switch”.
Creatively misusing the battery cover as some kind of switch.
Integrating an ON/OFFmicro switch
Adding an external, huge battery pack

However, if you have a close look at the circuit board, one could see, that there is an easy way to replace the existing, capacitive ON/OFF button with a slide switch, that physically cuts the power from the device. It is a non intrusive and self-explanatory modification of the device: Left is - as labeled - “OFF”, right “ON”. It even looks, as if the caliper has been manufactured like this. Nice! And all you need for this hack is a small 3D-printed part, some aluminium foil, super glue, and transparent tape. That’s it!

Step 1: Understanding the Working Principle

The existing red power button is removed and replaced by the 3D-printed slide switch. The slide switch uses existing parts of the housing as rails and guides. It has two small ridges, which help to keep the switch in its end positions. The slide switch is made conductive with a piece of aluminium foil. When moved, the foil connects the two, already exposed points A and B on the circuit board. To make the switch really work, the existing circuit paths need to be cut in point C and D. Another piece of aluminium foil finally helps to establish the correct ground connection of the board again.

Step 2: Printing the Switch

I have printed the switch with a layer height of 0.3mm and an infill of 100%. So as to get an accurate print result for this very small part, I had to slow down the print speed to 5mm/s on my printer.

Step 3: Plating the Switch

Next take a piece of aluminium foil and “plate” the switch with it using super glue. About half of the bottom, the front and parts of the top should be now covered with foil as shown in the picture.

Step 4: Preparing the Circuit Board

Use a small drill bit / engraving cutter to make a clean cut of the circuit paths in C and D. Around the circuits board’s rim, wrap a second piece of aluminium foil which connects A and E. Press it firmly on the board. The circuit lines should become visible through the foil. Then fix the foil with some transparent tape on the front and on the back. Note: On the front, apply tape only between the boreholes. The rest of the aluminium foil needs to be left uncovered since our aluminium plated switch will make contact here. Finally, take a multimeter / continuity tester and check the connections: There should be a connection from A to F, but no connection from A to B.

Step 5: The Tricky Part: Make the Slide Switch Work

If necessary, use an exacto knife to remove some of the foam on the backside of the display. Now put in the aluminium plated slide switch. The rest of the assembly is a little bit of playing around. The switch might work on the first go. Or it might not. Then you might need to add some tape only on the tip of the switch to get more downward pressure so as to get a proper connection to B. You also might need to loosen not only the screws that hold the circuit board in the housing, but also the screws which hold the housing on the caliper itself. The screws might affect free movement of the slider as well as contact of the slider with B. But if the screws are too loose, they might also affect the precision of the measurement. Maybe, you also need to resolder B to have a better contact? It is a little bit tricky to find the right mixture. And all in all, it is not a perfect solution, but a hack. Maybe the perfect solution would be, to combine my slide switch approach with the micro switch approach mentioned above? The only difference: The switch would point to the inside of the housing, not to the outside, i.e. the slide switch is just of made of plastic and pushes the micro switch with its tip.