A talented Maker by the name of Felix Rusu has designed a wireless PIR sensor node built around the ATmega328-based Moteino, an uber-mini board with solder pads for RFM12B and RFM69 radio transceivers.
As HackADay’s Brian Benchoff notes, the inexpensive radios – priced at approximately $4 each – are capable of transmitting about half a kilometer at 38.4 kbps, a rather impressive amount of bandwidth, especially for a very inexpensive system.
“The important bit on this wireless sensor, the PIR sensor, connects with three pins – power, ground, and out,” Benchoff explained. “When the PIR sensor sees something it transmits a code the base station where the ‘motion’ alert message is displayed.
Rusu, who is also a systems engineer, described the schematic/wiring as “trivial.”
“The PIR sensor can take anywhere from 5V to 9V or even more, [although] I used a 9V battery since it’s pretty compact. Later I want to try using lipos with a Moteino shield I am working on. The OUT pin goes high for a specific length of time when motion is detected (adjustable by side pot, I turned mine to minimum to limit LED power consumption). The sensitivity is also adjustable by another small side pot,” Rusu wrote in a recent blog post.
“The wonderful thing is that this PIR sensor is very cheap and uses about 60uA when idle and about 200uA when active! Coupled with a low power LED for visual indication the overall power consumption is very low. Of course the Moteino and everything on it has to be put to sleep. The OUT pin is connected to a low power 2mA red LED and to the hardware interrupt INT1 (digital pin D3 of Moteino). This way the sketch sleeps indefinitely, and when motion is detected the LED lights up and Moteino wakes up and quickly sends an ACK-ed ‘MOTION’ alert message.”
Interested in learning more? The low power Moteino sketch along with case plans are available here on Github.
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