January 2006, Issue 186

Electronic Scarecrow

OUTGOING PACKETS

After the replies are processed, the code figures out whether or not it’s time to send a packet. If the last sent packet wasn’t acknowledged, it’s sent again. Otherwise, it checks whether or not a new request packet is needed.

A data packet is sent if the sensor status changes from the last time it was sent. The data packet contains the current sensor status and a sensor data value.

If a switch is activated, indicating that you want to enable or disable the system remotely, an enable/disable packet is sent along with the switch status. This enables you to enter the protected area without triggering the system. You can enable the system again when you leave.

If it’s time to send a ping, the sensor test routines are executed and the results are sent along with the battery and charger voltages. If enough time has passed that the sensor offsets may have drifted, they’re reread as well.

A download data request packet is sent when Download mode is enabled. The packet is sent using maximum transmit power. It’s followed by a longer receive timeout than usual in order to boost the integrity of the download process.