Brymen BM857

Brymen BM857

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
Website	brymen.com

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.

Hardware

Multimeter:

• 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

Cable:

• TODO

See User_talk:Mrnuke#BM857_PC_Interface_cable

Photos

Multimeter:

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  Box

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  Mughsot

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  Device, back

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  Package contents

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  Probe cable storage clips

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  LCD Backlight

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  Holster removed, front

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  Holster removed, back

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  Case opened

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  Rear cover

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  Front cover

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  Rear cover, PCB removed

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  Upper PCB, top

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  Upper PCB, bottom

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  Main PCB, top

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  Main PCB, bottom

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  High voltage isolation slots.

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  High voltage isolation walls, designed to fit in the isolation slots.

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  Input circuit near the V jack

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  Microcontroller (right), and LCD controller (left)

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  Microcontroller (right), and LCD controller (left)

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  LCD controller and connector

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  ICs on the main PCB

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  More ICs

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.

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  Cable hookup

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  Cable hookup, detail

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  Cable hookup, closeup

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  Cable hookup, top detail

Protocol

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.

Resources

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