Difference between revisions of "RadioShack 22-812"
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The device periodically sends 9-byte packets at 4800 baud, 8n1. | 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. | The packet includes a mode indicator, payload and checksum. the payload is a 1-1 mapping of the LCD segments. | ||
{| border="0" width="95%" style="font-size: smaller" class="alternategrey sigroktable" | |||
|- | |||
! style="width: 3em;" | Byte | |||
! style="width: 3em;" | 7 | |||
! style="width: 3em;" | 6 | |||
! style="width: 3em;" | 5 | |||
! style="width: 3em;" | 4 | |||
! style="width: 3em;" | 3 | |||
! style="width: 3em;" | 2 | |||
! style="width: 3em;" | 1 | |||
! style="width: 3em;" | 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 | |||
|} | |||
The segment lettering is | The segment lettering is | ||
Revision as of 23:03, 19 October 2012
The Radioshack 22-812 is a 4000 counts, CAT II handheld digital multimeter with RS-232 connectivity. The 22-812 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 22-039. It is not yet clear if the Radioshack 22-039 is the same device as the 22-812.
Hardware
The micro-controller 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 front.jpg
...
Device, angle
RS-232 connector
Cover removed, front
Cover removed, back
Battery location
Opened up
PCB removed
PCB, front
PCB, back
Buttons PCB
RS-232 module
RS-232 transmitter
RS-232 PCB, top
RS-232 PCB, bottom
Banana sockets connecting to PCB
Spare fuse
Chip
Calibration pots
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.
| 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 |
The segment lettering is
|--A--| | | F B | | |--G--| | | E C | | |--D--|
The mode is given by the following table:
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
- rs22812.py project page (Python interface to Radio Shack 22-812 DMM)
- Radioshack 22-812 user manual