Serial Relative Humidity and Temperature Meas RH #160

Peter H. Anderson
915 Holland Road, Bel Air, MD 21014,

Sample PC Interface using Liberty Basic (Mar, '05)


This is an assembled unit which interfaces with a PC COM port and provides the capability of measuring the relative humidity and temperature using a Sensirion SHT-71 sensor. It includes an assembled printed circuit board, a 12 VDC wall power unit, and a six foot serial cable (DB9) . The unit interfaces with a COM port or similar at 9600 baud. (A USB to RS232 converter may be used).

When any character is received by the unit, a temperature measurement and relative humidity is performed and the result is returned to the PC;

28.62 55.13
Note that the temperature is in degrees C.

If a communications error occurs, the temperature and RH is returned as;

-88.88 -88.88

The PCB is professionally fabricated. However, it was adapted from another design and includes a minor amount of hand rework.

The module includes a female DB9 connector, RS232 level shift circuitry, an on-board 5 VDC supply, a Microchip PIC processor, the SHT-71 sensor mounted on an SOIC to 8-pin DIP adaptor which is mounted in a socket and a two conductor screw type terminal block. There are three hole on the PCB to permit the user to mount the module in a box or on a plate. Three standoffs and #4-40 screws are provided.

The processor may be reset by momentarily connecting the two leads on the terminal block. This should not normally be necessary.

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