Voltcraft VC-840
The Voltcraft VC-840 is a 4000 counts, CAT IV (600V) handheld digital multimeter with RS232 or USB connectivity.
Hardware
Multimeter:
- Multimeter IC: Fortune Semiconductor FS9721_LP3 (datasheet)
- Low power, True RMS-to-DC converter: Analog Devices AD737J (datasheet)
- Unknown SO-8 chip: ?
- Crystal: likely 4MHz (not verified, though)
- Fuses: 10A/250V and 500mA/250V (one glass fuse, one HRV fuse)
RS232 cable:
USB cable:
Photos
Multimeter:
Device, front
Device, back
Device, back w/o battery
Battery 1
Battery 2
PCB, back
PCB, front
Analog Devices AD737J
Fortune Semi. FS9721_LP3
RS232 cable:
See Multimeter cables#UNI-T_UT-D01.
USB cable:
See Multimeter cables#UNI-T_UT-D04.
Protocol
The connection to the PC is done using a cable which converts the optical signal (IR) on the multimeter to RS232.
The serial connection uses 2400 baud (hardcoded, cannot be changed) with 8n1 settings. The multimeter transmits 14-byte data packets periodically, the host can not send any commands whatsoever, only read the transmitted data.
A short protocol description is available from Voltcraft/Conrad. And another one.
TODO: Optional USB cable.