View source for RadioShack 22-812

{{Infobox multimeter
| image           = [[File:radioshack_22_812_front.png|180px]]
| name            = RadioShack 22-812
| status          = supported
| source_code_dir = serial-dmm
| counts          = 4000
| categories      = 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         = [https://www.radioshack.com/search/softwareResults.jsp?kw=22-812 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 [https://www.radioshack.com/product/index.jsp?productId=12988573 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 ==

<gallery>
File:radioshack_22_812_front.png|<small>Mugshot</small>
File:radioshack_22_812_angle.jpg|<small>Device, angle</small>
File:radioshack_22_812_interface.jpg|<small>RS-232 connector</small>
File:Radioshack_22_812_nocover_front.jpg|<small>Holster removed, front</small>
File:Radioshack_22_812_nocover_back.jpg|<small>Holster removed, back</small>
File:Radioshack_22_812_batt.jpg|<small>Battery location</small>
File:Radioshack_22_812_inside.jpg|<small>Opened up</small>
File:Radioshack_22_812_pcb_removed.jpg|<small>PCB removed</small>
File:Radioshack_22_812_pcb_front.jpg|<small>PCB, front</small>
File:Radioshack_22_812_pcb_back.jpg|<small>PCB, back</small>
File:Radioshack_22_812_button pcb.jpg|<small> Buttons PCB</small>
File:Radioshack_22_812_transmitter.jpg|<small>RS-232 module</small>
File:Radioshack_22_812_transmitte_module.jpg|<small>RS-232 transmitter</small>
File:Radioshack_22_812_transmitter_top.jpg|<small>RS-232 PCB, top</small>
File:Radioshack_22_812_transmitter_back.jpg|<small>RS-232  PCB, bottom</small>
File:Radioshack_22_812_terminal.jpg|<small>Banana sockets connecting to PCB</small>
File:Radioshack_22_812_fuse holder.jpg|<small>Spare fuse</small>
File:Radioshack_22_812_chip.jpg|<small>Multimeter IC</small>
File:Radioshack_22_812_calibration.jpg|<small>Calibration pots</small>
</gallery>

== 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 ===

{| border="0" 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
! colspan="8" | 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
! colspan="8" | Checksum

|}

=== Segment lettering ===

{{7seg|A|F|B|G|E|C|D}}

=== Mode byte ===

{| border="0" style="font-size: smaller" class="alternategrey sigroktable"
|-
! style="width: 2em;" | 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 ==

* [http://code.google.com/p/rs22812/ rs22812.py project page] (Python interface to RadioShack 22-812 DMM)
* [http://www.radioshack.com/graphics/uc/rsk/Support/ProductManuals/2200812A_PM_EN.pdf RadioShack 22-812 user manual]

[[Category:Device]]
[[Category:Multimeter]]
[[Category:Supported]]