While I was on vacation I kept panicking, thinking that something or someone would cause harm to my home. I’ve got a server that is capable of sending text messages (SMS) to my mobile phone using my providers web interface…
So…
Why couldn’t I set up a security system using a few 1-wire sensors installed in a PIR “security??? motion sensor light? The logic to run the PIR sensor is TTL… When motion is detected it causes a data line to go high. Couldn’t a 1-wire device read that high input as an alarm?
Here are some thoughts…
ACE hardware ACE hardware Par Lamp Motion Sensor; chosen becayse it is the cheapest PIR sensor I could find.
DS2720 using the Power-Switch Sense input; chosen because it was the cheapest “sensor.???
Set the 1-wire controller or TINI to poll the DS2720 at a set interval to check to see if there is motion.
Create an entry for this at the project management website. My company has considered doing very similar things using 1-wire. It seems that 1-wire is the perfect protocol for a wired, modular, exandible, and robust security system.
Ok, will do. I was thinking the same thing…
I did some investigation with a motion sensor that I had… It wasn’t one of the ACE models, but it might be similar… It seems to function only on 24V. Nothing happened when I tried to inject 5V to the 5V rail. I don’t have a 24V power supply to inject power on the 24V line… I did find the line that goes high when the sensor is activated.
It looks like it would be easy to power the sensors with 120V and use an opto isolator connected from the ‘high line’ to the 1-wire sensor-network.
It might be worth the efforts at that point to find a motion sensor that can run off of 5V or even 12V. That way, it can snag power from the 1-wire bus — Or, at the very least, we can have a 12V line going along the same cable to power it. In most installations, the sensors are going to be nowhere near a 120v power outlet. Also, that makes complications with battery backup when the criminal cuts the mains off.
The extra price in a lower-voltage sensor may justify the price of a 120v transformer plus a UPS on each sensor!!
Here’s the funny part… I can’t seem to find an electronic supplier that carries the PIR sensors for less than $60. The sensor run off of 5V. The LM339 runs off of 5V.
If need be, the cheap ACE motion sensors can be purchased and the PIR sensor and LM339 could be removed and rewired to another circuit, thus allowing them to leach on the 1-wire network. Problem solved.
Thinking back… I’ll bet that when I was applying 5V to the 5V section of the circuit there was a diode preventing proper execution. I’m going to try to remove the 24V section and just power the system with 5V again. I’ll take pictures this time.
I finally got around to running the PIR sensor off of 24V… The first sensor that I tried worked perfectly. It has two LM339 opamps… I don’t know who makes this one. It’s a really old sensor.
The ACE Hardware unit has an almost identical circuit layout except they have a custom silicon circuit replacing the two LM339’s. Unfortunately, it arc’d pretty well as soon as applied the 24V. I’m not sure if that was because I missed the 24V point or it just couldn’t handle it.
Speaking of PIR… After my conversation with Brian about not being able to find any PIR sensors for less than $60:
Nicera infrared detector module for $3.95.