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Va va40b mugshot.png
Status supported
Source code serial-dmm
Counts 6000
IEC 61010-1 CAT III (1000V) / CAT IV (600V)
Connectivity USB/serial
Measurements voltage, current, resistance, capacitance, frequency, temperature, duty cycle, diode, continuity
Features autorange, data hold, relative, min/max, backlight
Website mastech.com.cn

The V&A VA40B is a 6000 count CAT III (1000V) / CAT IV (600V) handheld digital multimeter with USB connectivity.

See V&A VA40B/Info for more details (such as lsusb -v output) about the device.

Note: The company V&A ("SHANGHAI YIHUA V&A INSTRUMENT CO., LTD, known as Mastech Shanghai") has apparently been part of (or related to) MASTECH in the past, and also sells some multimeter models that have been sold by MASTECH in the past.1

The manufacturer name isn't stated anywhere on the device, package or manual. The Velleman DVM4100 model looks identical to the VA40B, except for its labels and blue case color, but their protocols differs. The VA40B also has some similarities with the V&A VA18B and the PeakTech 3415.



  • Fuses: F 0.63A/1000V D10,3*38, F 10A/1000V D10,3*38 (values from the manual)
  • TODO

USB cable:



14-byte LCD segments over USB-to-serial (Prolific chip, 2400 baud, 8n1). The DMM IC used in this multimeter is probably a Fortune Semiconductor FS9721_LP3 or a Dream Tech International DTM0660 with protocol options set accordingly.

The manufacturer specific last byte of the 14-byte packet (numbered 0xe) is as follows:

Byte Bits 7-4 Bit 3 Bit 2 Bit 1 Bit 0
13 0xe MIN (unused?) °C MAX

To enable output to the PC on the multimeter you have to keep the Hz/DUTY key pressed while powering on the device. However, it will auto-poweroff (after roughly 1 hour?), even in this mode. To avoid that, press both the Hz/DUTY and the SELECT key during power-up (see manual page 19).