Remote Event Detector
This device listens for 'crickets' - little transmitters that bleep out their condition periodically.
| The receiver unit shown
here uses a $10, 433 mhz receiver module feeding a PIC16F84 microcontroller.
The RF module has both digital and analog outputs. As it turns out,
the digital output is not good to use because it always puts out some kind
of data (noise) and tends to 'annoy' the processor. As you can see
from the schematic, the analog output was used
instead and the level detection is done externally.
All of the circuitry is built on the front panel. This includes the input for In Circuit Programming. The design specifies 4 channels for each transmitter unit. A separate bit is sent depending on whether the status of the sensing inputs has just changed or whether the status is just being reported on a scheduled time.
Two of the transmitter units are shown here. The one on the left is the full circuit (as shown in the transmitter schematic), and the one on the right is a 'minimal' transmitter.
To save on battery power, and to allow for RC oscillator operation, the data is sent using Ten Pulse data encoding. This type of coding has proven useful in several projects. Also, the circuit switches to a slow clock rate while waiting for an external input to change and also keeps track of time to do scheduled events.