Designing Embedded Hardware, 2nd Edition

PIC-Based Environmental Datalogger

Now let's look at a complete system based on a PIC processor. The design presented here is a simplified version of my DL4 datalogger product. This datalogger is designed for extended recording of data (for at least a year), using a minimum of power. It has 1M of nonvolatile memory, capable of retaining data without power for as much as 20 years. The sensors fitted are light and temperature, but you could easily adapt this design to record any analog sensor you like, from acceleration to magnetic field. It's also small. The entire datalogger fits onto a circuit board smaller than your smallest finger.

The processor is a PIC16LF873A, a variant of the PIC16C73. The "L" means that it is low-power, and the "F" means that it is a flash-based part (rather than EPROM or OTP) that can be reprogrammed in-circuit, making debugging (and life) so much easier. The "8" indicates that the processor includes EEPROM for nonvolatile parameter storage, useful for holding user preferences and machine state. Finally, the "A" tells us that it is a second revision (version) of the silicon. The basic circuit for the processor and its support components is shown in Figure 14-6.

Figure 14-6. Datalogger processor and support components

Note that the processor's power pin is connected to a net labeled PVDD rather than the system's VDD. Since the processor can be reprogrammed ...