The Conrad Electronics MM3610D is a digital multimeter manufactured by Metex (Korea) and sold under the Conrad Electronics brand. It connects to a PC via a passive 5-wire RS-232 serial cable that uses a proprietary 5-pin Conrad special connector at the multimeter end and a standard DB-9 female connector at the PC end. The cable contains no active components; instead, the DTR and RTS control lines from the PC supply the small current required to power the multimeter’s opto-isolated receiver circuit passively. The instrument communicates using the Metex 14-byte ASCII protocol at 600 or 1200 baud, 7 data bits, no parity, and 2 stop bits (7n2).
9 PIN D-SUB FEMALE to PC
5 PIN UNKNOWN CONNECTOR to the multimeter
| PC | Conrad | Dir | |
|---|---|---|---|
| Request To Send | 7 | 1 | OUT |
| Receive Data | 2 | 2 | IN |
| Transmit Data | 3 | 3 | OUT |
| Data Terminal Ready | 4 | 4 | OUT |
| Ground | 5 | 5 | - |
Signals
- RTS (Request To Send) — DB-9 pin 7; Conrad pin 1. Must be held OFF (de-asserted, logic low) during operation. The RTS line passively powers the multimeter’s opto-isolated receiver circuit; asserting it high disrupts the circuit.
- RxD (Receive Data) — DB-9 pin 2; Conrad pin 2. Serial data received by the PC from the multimeter.
- TxD (Transmit Data) — DB-9 pin 3; Conrad pin 3. Serial data sent from the PC to the multimeter. The multimeter responds to a single-character query (typically 0x44, ‘D’) by returning a 14-byte ASCII measurement string.
- DTR (Data Terminal Ready) — DB-9 pin 4; Conrad pin 4. Must be held ON (asserted, logic high) at all times to supply operating current to the multimeter’s receiver circuit via the RS-232 driver output.
- GND (Signal Ground) — DB-9 pin 5; Conrad pin 5. Common signal reference for all lines.
Notes
The proprietary 5-pin Conrad special connector at the multimeter end is physically and electrically distinct from the generic Metex 5-pin RS-232 connector used on related models such as the Voltcraft M-3650CR and MASTECH MAS345; the pin numbering and signal order differ between the two connector types and the cables are not interchangeable. The serial port must be configured with DTR asserted and RTS de-asserted before the multimeter will respond. Protocol parameters: 600 or 1200 baud, 7 data bits, no parity, 2 stop bits (7n2). On each query the multimeter returns 14 ASCII bytes: a 2-character mode field, a space, a sign character, a 5-character value with embedded decimal point, a 4-character unit field, and a carriage return (0x0D).
References
- Metex M-3610D / M-3650D Digital Multimeter Manual — Metex Corporation