Functional and data logging considerations

A project log for Data logger device for DM3058 digital multimeter

Small device that connects to serial port of DM3058 bench top multimeter to retrieve and log measurements

KristsKrists 08/05/2019 at 10:050 Comments

Initial development on data logger device started sometime by the end of last year. First steps were to test serial commands according to programming manual and see how they can be used. After some tweaking it seemed that correct way would be let data logger to trigger measurement, wait when it’s ready and issue command to read value. All measurements from multimeter are reported as numbers in scientific notation like 1,506540-E10 so that text string is uniform regardless of actual value. To have values meaningful in log files data logger should query active measurement mode as well. Fitting reasonable amount of data in 16-megabit SPI flash requires converting values to binary format. When mounted as USB mass storage logger would decode these records and present them as text files in file system. I had some knowledge on how FAT file system works, but had to do a good refresh. About the X-mass time I was thinking more about FAT entries and partition records that anything else. It was fun time though and I got it working. I was able to built virtual file system on the fly, as there is no real memory available for data in plain text format. It works not very fast, though.

So it looks that device should have some pig-tail connection to serial port on back of muiltimeter so it can be connected and removed as needed rather fast. I might use RJ45 connector for this. I don’t quite like that locking tab on RJ45 plug is prone to breaking but sockets, connectors and protective boots as well are readily available. I would need just 6 wires for connection. So called British Telecom telephone plug looks like a good choice, but solderable small sized PCB sockets for these are not widely available.