1-Wire PIR
| In each room in my house I'm installing a Passive Infra-Red (PIR) sensors to detect people moving. These are used by my Home Control System to detect occupancy and intrusion. These are fairly standard alarm sensors which use a 12Vdc, low current supply. The only unique thing about them is that I've chosen a model (Elite Security Products - Quest PIR) is that it is low current (<15mA) and one that includes a small relay, in order to simplify the interfacing. The relay is basically used as a normally closed switch. These PIRs work with anything from 9V to 16V. |
| This is the inside of the PIR detector. The useful thing is that I can run standard burglar alarm wire from this remote sensor to my 1-Wire PIR unit. |
1-Wire PIR Unit
My intial plans were to create a board for each PIR but, I decided to simplify the wiring and my 1-Wire Network by creating a single unit that can support 7 PIR sensors and acts as one single node on my 1-Wire Network. In addition the unit has a twilight sensor connected to it and provides a twilight feed back down the PIR sensors, which is used by each Night Light Controller.
Each PIR sensor and my twilight sensor have a 12V feed and thus provide a 12V signal, which is too high to feed into a 1-Wire device. I've used an opto-coupler (isolator) to seperate the 12V side from the 5V 1-Wire side. The current is limited to 3mA into the opto-coupler emitter using a resistor. I've used two quad-ILQ74 devices to provide isolation for eight DS2405 devices, one of these being the twilight sensor though. The useful thing about the DS2405 is that it can store activity detected. This is required because the PIR output is a 1 second pulse and you may query the device after this pulse has occured and think the PIR had not detected a person.