I've been looking ito the idea of a cheap DRO for X Y and Z axis, not essential I know for a CNC mill but a nice to have for reassurance and for manual operation. The cheap Lidl and Aldi Digital calipers all seem to use the same basic design of of display and linear position circuit board that works on some clever capacitive non contact arrangement with the bar it slides on. The small 150 mm calipers are not just limited to that length either as I have removed the display head and you can carry on sliding it along and the display keeps on going for at least 700 mm or more. The best thing though is they all have a gold plated edge connector which can be used to transmit the digital read-out signal to a remote display. The output is a 24 bit digital signal with a timing clock and the value is transmitted every 320 ms (about 3 per second). Negative values are supported as well. The value is transmitted in both imperial inches as well as metric to 0.01 mm resolution. The 4 pin connector connects to power (1.5 V and 0V on my workzone) and the other two pins are clock (timing) and data. The whole data word (all 24 bits) is transmitted in 100 uS in 7 bursts of 4 bits so actually there are 28 bits. I have yet to fully decode the bits but I assume they are a binary word according to the chinese converted to english manual

When the unit switches off after a timeout (on my workzone) it is actaully still transmitting so just the local display switches off. So, no need to worry about this, but I think the powerfix version with the 3V CR2032 cell may fully switch off after a timeout of idle, I need to check.

I need to work on figuring out the code of the transmitted value but once understood a small PIC processor could be developed to drive a large segment digital display in the correct units.

More work is needed but at £8.99 a shot these calipers are worth modifying and fitting to your machine as a pretty darn accurate DRO.

If anyone has figured the serial code or has already solved this I would love to know, there is no point in reinventing the wheel.

PS: I have tried to get hold of a connector and cable plus remote software for a PC but although this is hinted at being available I can't find a source. These are imported devices from China and the UK importers are completely useless.

Some of you may be interested in the developments of this project for your own machines.

john