TekPower TP4000ZC
The TekPower TP4000ZC is a 4000 counts, CAT II (600V) handheld digital multimeter with RS232 connectivity.
This multimeter appears to be a rebadged Digitek DT4000ZC.
Hardware
- Multimeter IC: The microcontroller is an unidentifiable plastic blob. The communication protocol points to Fortune Semiconductor FS9721_LP3 (datasheet)
- LM358 opamp
- HEF4013BT flip-flop
The RS-232 connector is a standard 3.5m stereo jack, with the ring left unconnected. The transmitter is optically insulated from the rest of the device. The DB-9 connector has a loopback resistor between the RX and TX pins.
Photos
Device, angle
Mugshot
Device, back
Package contents
Holster removed, front
Holster removed, back
Battery compartment
Rear cover
Front cover
Rear cover, PCB removed
PCB, front
PCB, back
Chip
HEF4013BT flip-flop
LM358 opamp
RS-232 optoisolation
RS-232 module
RS-232 PCB, bottom
RS-232 PCB, top
Supplied RS-232 cable
RS-232 cable, disassembled
RS-232 cable, detail
Protocol
The device periodically sends 14-byte packets at 2400 baud, 8n1. The MSB nibble of each byte indicates the byte number. The payload is composed of the LSB 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 | hFE | Celsius | Reserved | Reserved |
Segment lettering
| C | ||
| B | G | |
| F | ||
| A | E | |
| D |