Brymen BM857

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Brymen BM857
Bm 857 mugshot 500000.png
Status supported
Source code serial-dmm
Counts 50000, 500000(DCV), 999999(Hz)
IEC 61010-1 CAT III (1000V) / CAT IV (600V)
Connectivity RS232
Measurements voltage, frequency, diode, resistance, continuity, capacitance, current
Features autorange, data hold, crest, backlight, true-rms, dBm (selectable impedance), %4-20mA
Website BM857s BM859s

The Brymen BM857 is a 50000 counts (500000 DC V), CAT III (1000V) / CAT IV (600V) handheld digital multimeter with RS232 connectivity. The BM859s is also supported, it uses the same protocol. Adapter kits ship with IR to RS232 cables, and include RS232 to USB converters.

Higher end models support dual temperature sensors and difference mode, and the reference impedance for dBm measurements can be chosen in a range between 4 and 1200 Ohms.



  • Multimeter IC: TBD
  • Precision +2.5V Voltage reference: Analog Devices REF43
  • True RMS-to-DC converter: Analog Devices AD737
  • EEPROM(?): Chip marked S24C0.
  • Unidentified: Several 062-JRC chips. These appear to be JFET opamps.
  • Unidentified: Two QFP64 chips.
  • TODO





This can use either the BC-85X or the BC-85X-1 cables. See Device_cables#Brymen_BC-85X(-1).

Currently, mrnuke is working on an improvised USB-to-infrared converter cable. See User_talk:Mrnuke#BM857_PC_interface_cable for more details.

Newer models (BM850a/BM850s) are said to require the BU-85Xa adapter. These different versions of meters and adapters are not compatible to each other.

BM850s series

The BM857s and BM859s meters (the BM850s series) uses the same protocol and works with the BC-85Xa adapters.


Serial communication (genuine COM port), textual presentation of measurement values (floating point, normalized mantissa plus exponent), combined with binary bit fields for current meter's function and thus measured unit, variable length records with control chars in the header/footer (DLE, STX/ETX) around the mode flags and value's text, up to 22 bytes per DMM packet. See resources below for a full description of the protocol.