Reverse engineering: Wintex TD2200

work in progress

The Wintex TD2200 is a digital handheld multimeter of Korean provenience. It seems to have a decent accuracy (0.1% on DC voltage). It also contains a RS232 port for communication with the computer. The package I got also contained a RS232/USB converter with the CP210x chip (driver here). The multimeter has a miniUSB connector (pinout to be determined) for RS232; the interface cable has a miniUSB on one end and a Canon 9F (standard RS232) on the other end. The interface is optoisolated.

The meter is built around the Cyrustek ES51922 (local copy) chip.

The software coming with the device is fairly lousy and Windows-only. However it does the basic data collection job.

On hardware level, the communication protocol is 7bit, 19200 baud, no parity, no handshake.

On software level, the meter sends a line of 12 ASCII characters per measurement (typ. several per second), example (mV, small fluctuating voltage) here:

401344;40080{0D}{0A}
401322;40080{0D}{0A}
401256;40080{0D}{0A}
400061;00080{0D}{0A}
401480;40080{0D}{0A}
402299;00080{0D}{0A}
406057;00080{0D}{0A}
400341;40080{0D}{0A}
400419;40080{0D}{0A}
400466;40080{0D}{0A}
400514;40080{0D}{0A}
400553;40080{0D}{0A}
400498;40080{0D}{0A}
401566;40080{0D}{0A}
400322;40080{0D}{0A}

• The character 0 probably means the value overall magnitude.
• The characters 1..5 correspond to the five digits on the display.
• The character 6 seems to be changing with the measurement type. (Function.)
• The character 7 seems to have one bit as the value sign. Also serves as status byte.
• Bit 3 is 1 for °C and 0 for °F
• Bit 2 is sign (pos/neg)
• Bit 1 is battery status (1 if battery low)
• Bit 0 is OL (input overload, 1 if over range)
• The remaining 4 bytes determine the options. (The chip datasheet describes the format!)

The RS232 nature of the device seems to allow its connection to other electronics as a data acquisition unit. A wireless bridge, e.g. mediated via wifi, can be also used to connect it to the data collection server. A Bluetooth/UART converter could be used for connecting it to a cellphone.

The meter can measure temperatures using a K-type thermocouple. The value can be adjusted with a small SMD trimpot (VR4), located on the board between the Power and Light buttons.

The TD2200 contains the following chips:

• U1: ES51922, the heart of the device
• IC3: 2904, an op-amp? Connected to pin 31(internal AC-DC op-amp output), weird
• IC4: AD737J, a true RMS converter, for accurate AC measurements
• IC5: OP07, op-amp for thermocouple
• IC6: HEF4053BT, three 1-of-2 analog selectors, associated with measuring of inductances
• IC7: NJU4011B, quad-NAND gate, associated with measuring of inductances
• IC8: OP07, op-amp for buffering signal from C41:R43 filter of output from IC6
• IC9: OP07, op-amp for amplifying output of IC8
• IC11: some tiny SOT-25 thing, E1E code, maybe voltage regulator? possibly R3116N, namely R3116N351C, Ricoh low voltage detector
• IC12: 817B, RS232 input optocoupler (to enable RS232 output, connects to pin 111)
• IC13: 6N137, RS232 output optocoupler (for the RS232 output, connects to pin 123)

Functional blocks, adjustable elements association

The multimeter is internally quite similar to Uni-Trend UT61E, with additional circuitry for measurement of coils and for thermocouple handling.

• VR1: 20k multiturn trimpot, between voltage input and pin 19(OVX, inputH for resistance measurement), equiv. VR3 in UT61E, datasheet says it calibrates the C2 (220nF) rangeA
• VR2: multiturn pot, reference voltage adjustment for pin 38, equiv. VR1 in UT61E
• VR3: multiturn pot associated with AD737, likely VR4 in UT61E
• VR4: SMD trimpot, offset adjustment for IC5, sets temperature from thermocouple
• VR5: multiturn smaller trimpot, gain adjustment for IC9
• VR6: SMD trimpot, offset adjustment for IC8
• VR7: single-turn trimpot associated with the input frequency compensation for pin VR1
• VR8: (not on board? cannot find it)
• VR9: multiturn pot, connects to pins 48/49 where the 1k/9k resistors for cap measurement are, probably adjusts capacitor measuring

• TC1: tuning capacitor, probably freq comp for VR1 input
• TC2: tuning capacitor, connected to pin 25(VR3), probably freq comp for range attenuator
• TC3: tuning capacitor, connected to pin 26(VR2), probably freq comp for range attenuator

Images

Without cover	Display removed	Main chip	Main chip
Optoisolated serial output	Back side	Back side, under display	Cover inside
Cover outside