Problems with modern scales
Currently we are working on a number of problems with the modern capacitive style scales. 600mm miniUSB Readout Bar is an example which we'll document further soon. This has an earth problem when used with other scales in the range, but can be modified to alleviate the problem. Once used with a BIN6 dongle, this scale can be used with the DRO350, or with the right cable, it can be used with the 550 or 375. While using miniUSB connectors on the scales seems to be a good idea, the lack of suitable mini-USB to mini-USB cables causes a problem, so a full USB socket on the DRO may be better. As an alternative, we are working on a right angle mini-USB to mini-DIN cable for those who are replacing existing scales on their existing DRO350 setup, and these may well be the more economic option for new builds as well.
Next problem to point out is that while the scales are powered by a 3V battery, this is NOT connected to the power pin on the mini-USB connector. As indicated above, some scales do not have the -ve side of the battery connected to the metalwork either, which creates even more fun, but while is possible to modify the scales to be powered from the mini-USB cable, this pin is actually used by the intended remote display to switch between inch and mm. That is al least some of the scales I've had access to. This then highlights another difference with the scales, the 'steps per inch' setting changes between imperial and metric mode, being 2000 for imperial and 2540 for metric. As long as one is not switching the SCALE end setting either can be used at the DRO end, but if it gets changed at the scale end, the DRO setting needs to be changes as well. I've not had one of the new style remote displays to play with, so can't confirm how this works with those, and not all scales seem to support allowing the display to change the setting via the power pin on the mini-USB socket, but in all cases the signal levels on the connector are still only 1.5V swing, so setting the DRO to provide 3V may result in the clock and data not getting sliced in the comparator. The scales do provide both data and clock so do not follow the 'igaging' format which provides a 3V clock signal from the display end.
Further work on the older scales is giving some insight to problems such as the occasional 0.2" or the lockup when switching on and off where the scales are powered from the DRO. Notes on Old Scales is a growing repository of information.