Introduction.
The RH #161 Module is an assembled unit which interfaces with a PC COM port and provides the capability of measuring the relative humidity and temperature using two SHT-71 sensors, one local and one remote. It includes an assembled printed circuit board, a 12 VDC wall power unit, and a six foot serial cable (DB9). It also includes a a small assembled remote circuit board which includes the remote SHT-71 sensor.
The unit interfaces with a COM port or similar at 9600 baud. (A USB to RS232 converter may be used).
One SHT-71 is locally located with the PIC processor. The other is mounted on a small circuit board with a four screw terminal block. The interface between the local unit and the remote is via four conductors; +5 VDC, GRD, SCK and DATA. I have implemented this using telephone terminals as shown and a 100 foot modular telephone extension cable. (Note that the terminal blocks and the telephone extension is not included in this package).
When any character is received by the unit, a temperature measurement and relative humidity is performed using each of the SHT-71 sesnors and the results are returned to the PC;
L 28.62 55.13 R 25.43 65.21Note that the temperatures are in degrees C.
If a communications error occurs, the temperature and RH is returned as -88.88;
L -88.88 -88.88 R 25.43 65.21
If a sensor is not detected, no data is returned;
R 25.43 65.21
Note that in this case, the local sensor was not detected as being present.
The local PCB is professionally fabricated. However, it was adapted from another design and includes hand point tp point wiring.
The local module includes a female DB9 connector, RS232 level shift circuitry, an on-board 5 VDC supply, a Microchip PIC processor, an SHT-71 sensor mounted on an SOIC to 8-pin DIP adaptor which is mounted in a socket and a six conductor screw type terminal block. There are three holes 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 remote unit consists of a PCB, an SHT-71 sensor mounted on an SOIC to 8-pin DIP adaptor which is mounted in a socket and a six conductor screw type terminal block. There are three holes 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 on the local unit may be reset by momentarily connecting two leads on the terminal block. This should not normally be necessary.
The package is $39.95 plus $30.00 for each SHT-71 sensor mounted on an SOIC to 8-pin DIP. Thus, $99.95 for the complete package including two SHT-71 sensors.
