Skip to content

RadioShack 22-812

RadioShack 22-812

RadioShack 22-812
Status supported
Source code serial-dmm
Counts 4000
IEC 61010-1 CAT II (600V)
Connectivity RS232 (standard DB9 connector)
Measurements voltage, temperature, current, resistance, capacitance, continuity, diode, logic, frequency, hFE, duty cycle, pulse width
Features autorange, data hold, min/max, dBmW (600Ω)
Website radioshack.com

The RadioShack 22-812 is a 4000 counts, CAT II (600V) handheld digital multimeter with RS-232 connectivity.

It is no longer sold under this part number, and for a while, it appeared to have been discontinued. RadioShack does sell a visually identical multimeter, the RadioShack 22-039. It is not yet clear if the 22-039 is the same device as the 22-812.

Hardware

The microcontroller is an unidentifiable plastic blob.

This devices has a standard DB-9 connector at the top, and does not require a special adapter cable. The RS-232 transmitter is optically insulated from the rest of the device. The transmitter uses a separate PCB, integrated into the multimeter's housing. The RS-232 module is powered from the serial port.

Photos

Radioshack 22 812 Nocover Back Radioshack 22 812 Nocover Back

Radioshack 22 812 Nocover Front Radioshack 22 812 Nocover Front

Radioshack 22 812 Pcb Back Radioshack 22 812 Pcb Back

Radioshack 22 812 Angle Radioshack 22 812 Angle

Radioshack 22 812 Transmitter Top Radioshack 22 812 Transmitter Top

Radioshack 22 812 Batt Radioshack 22 812 Batt

Radioshack 22 812 Interface Radioshack 22 812 Interface

Radioshack 22 812 Pcb Front Radioshack 22 812 Pcb Front

Radioshack 22 812 Button Pcb Radioshack 22 812 Button Pcb

Radioshack 22 812 Front Radioshack 22 812 Front

Radioshack 22 812 Inside Radioshack 22 812 Inside

Radioshack 22 812 Terminal Radioshack 22 812 Terminal

Radioshack 22 812 Fuse Holder Radioshack 22 812 Fuse Holder

Radioshack 22 812 Transmitte Module Radioshack 22 812 Transmitte Module

Radioshack 22 812 Pcb Removed Radioshack 22 812 Pcb Removed

Radioshack 22 812 Transmitter Radioshack 22 812 Transmitter

Radioshack 22 812 Calibration Radioshack 22 812 Calibration

Radioshack 22 812 Chip Radioshack 22 812 Chip

Radioshack 22 812 Transmitter Back Radioshack 22 812 Transmitter Back

Protocol

The device periodically sends 9-byte packets at 4800 baud, 8n1. The packet includes a mode indicator, payload and checksum. The payload is a 1-1 mapping of the LCD segments.

Packet structure

Byte 7 6 5 4 3 2 1 0
0 Mode
1 Hz Ohms k M F A V m
2 u n dBm s % hFE REL MIN
3 4D 4C 4G 4B DP3 4E 4F 4A
4 3D 3C 3G 3B DP2 3E 3F 3A
5 2D 2C 2G 2B DP1 2E 2F 2A
6 1D 1C 1G 1B MAX 1E 1F 1A
7 Beep Diode Bat Hold - ~ RS232 Auto
8 Checksum

Segment lettering

  A  
   
F B
   
  G  
   
E C
   
  D  

Mode byte

Value Meaning
0 DC V
1 AC V
2 DC uA
3 DC mA
4 DC A
5 AC uA
6 AC mA
7 AC A
8 Ohm
9 Capacitance
10 Hz (dial set to Hz)
11 Hz (dial set to DCV)
12 Hz (dial set to mA/A)
13 Duty cycle (dial set to Hz)
14 Duty cycle (dial set to DCV)
15 Duty cycle (dial set to mA/A)
16 Pulse width (dial set to Hz)
17 Pulse width (dial set to DCV)
18 Pulse width (dial set to mA/A)
19 Diode
20 Continuity (beep)
21 hFE
22 LOGIC
23 dBm
24 (Unknown)
25 Temp

Resources