Issue 149 December 2002
Wireless Temperature Sensor Stew

rfPICDEM1 WITH TOUCH SCREEN

After I got the basics of the Easy GUI under my belt and saw it spitting data out on the Serialtest Async datascope screen, the rest of the process of putting together the wireless temperature sensor conversion process went smoothly.

Using the Microchip ICD in conjunction with the CCS PICC C compiler and MPLAB, I was able to leisurely port the rfPIC transmitter code over to the PIC16F877 in less than two days. Because the original wireless sensor application is based on the rfPIC12C509AG, all of the I2C and RF routines are based on a 4-MHz clock with a 1-µs cycle. All I had to do to get the temperature sensor to talk to the PIC16F877 was turn on the respective clock sources in the PIC16F877 and run the MPLAB-ICD demo board with a 4-MHz oscillator I had stolen from the PICDEM2 PLUS board.

To test the RF, I finally had to move to a 3.3-VDC platform to preserve the integrity of the transmitter’s original RF design. I dodged the build-it-from-scratch bullet again, because I was able to use an old 3.3-VDC project (i.e., S7600-A/PIC16F877 Internet engine) that has ICSP capability, an RS-232 converter IC, and a PIC16F877 in place and ready to go. All I had to do to migrate to the 3.3-VDC platform was program my PIC16F877 code with ICSP, twist the RS-232 TX and RX lines, and tie in the transmitter board control signals.

I have a lot of fun doing projects like this for Circuit Cellar; however, the idea behind the Future Electronics/ Microchip wireless sensor demo kit is to allow a designer to take the basic ideas behind the hardware and firmware and transfer them to his or her custom project without having to know a great deal about RF and sensor interfacing up front.

For this project, I just added a touch screen to the RF link. I never had to think about anything RF to make it happen, proving, once again, that it doesn’t have to be complicated to be embedded.