Multimeter ICs

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Revision as of 22:23, 1 November 2012 by Uwe Hermann (talk | contribs) (Fortune Semiconductor FS9922-DMM4)
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This page lists some information about ICs commonly used in various multimeters (DMMs).

Fortune Semiconductor FS9721_LP3/FS9721B

FS9721_LP3 on Voltcraft VC-820.
FS9721 (?) on TekPower TP4000ZC.

Protocol

The chip periodically sends 14-byte packets at 2400 baud, 8n1. The upper nibble of each byte indicates the byte number. The payload is composed of the lower nibbles, and is a 1-1 mapping of the LCD segments. The downside to this protocol structure is that transmission errors in the LSB nibbles cannot be detected. There is no checksum or CRC in the packet.

Packet structure:

Byte Bits 7-4 Bit 3 Bit 2 Bit 1 Bit 0
0 0x1 AC DC Auto RS232
1 0x2 Negative 1A 1B 1C
2 0x3 1D 1E 1F 1G
3 0x4 DP1 2A 2B 2C
4 0x5 2D 2E 2F 2G
5 0x6 DP2 3A 3B 3C
6 0x7 3D 3E 3F 3G
7 0x8 DP3 4A 4B 4C
8 0x9 4D 4E 4F 4G
9 0xa u n k Diode
10 0xb m % M Beep
11 0xc Farads Ohms Rel Hold
12 0xd A V Hz Low battery
13 0xe User bit 3 User bit 2 User bit 1 User bit 0

Segment lettering:

  C  
   
B G
   
  F  
   
A E
   
  D  

Fortune Semiconductor FS9922-DMM3

TODO.

Fortune Semiconductor FS9922-DMM4

FS9922-DMM4 in a UNI-T UT61D.

The Fortune Semiconductor FS9922-DMM4 (datasheet) is a widely used 6000-count auto-ranging DMM chip: it takes input from the various controls on the front panel, drives the LCD display, and can communicate its readings via a serial port.

Protocol

TODO