This project came about for two reasons. First and foremost I’ve got a detached garage where it’s difficult to see from inside the house if the garage door is open or closed. After multiple incidents of accidentally leaving the garage door open all night long, I knew I had to do something different.
Then, Hack-a-Day posted this article on a Open Garage Door Indicator for under $6, with a challenge to make a wireless version. Never able to pass up a challenge, I started designing…
Off to my favorite place, SparkFun , to look at cheap wireless interfaces. What caught my eye was the WRL-08946 / WRL-08949, transmitter / receiver pair. Less than $4 for the transmitter and $5 for the receiver. OK, so I won’t make the less than $6 challenge from Hack-a-Day, $9 for a transmitter/receiver pair is pretty dang cheap and 434Mhz/2400 baud aught to have been more than sufficient for signaling a switch open/close.
Comments on the SparkFun site seemed to indicate that some people were having problems getting this chip pair to work and that it might well be the automatic gain control causing the receiver to pick up trash data unless there was a continuous stream of transmitted data stream.
Armed with this information, I decided that I would start by using a pair of ATTINY13’s to encode and decode a continuous data stream. This in theory would get around any automatic gain issue and with some error correcting code would be able to recover from a missed bit every now and then.
Thus, on to the detailed assembly….