Brymen BM857

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Brymen BM857
Bm 857 mugshot 500000.png
Status supported
Source code brymen-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, dBmW1, %4-20mA

The Brymen BM857 is a 50000 counts (500000 DC), CAT III (1000V) / CAT IV (600V) handheld digital multimeter with RS232 connectivity.

1: The reference impedance is selectable from 4Ω to 1200Ω. It is not limited to reference impedance of 600Ω.



  • 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


  • TODO

See User_talk:Mrnuke#BM857_PC_Interface_cable




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.


Serial communication (genuine COM port), textual presentation of measurement values (floating point, normalized mantissa plus exponent), number codes 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 number and value's text, up to 22 bytes per DMM packet. See resources below for a full description of the protocol.


BM850/BM850a/BM850s protocol documentation download area and ZIP with PDF (worked as of 2019-06-10, vendor may change that)