I need to develop an interface for a "Recora Chair Occupancy Sensor": http://recoraco.thomasnet.com/viewitems/bed-chair-occupancy-sensors/recora-chair-occupancy-sensor-cos-?#
The sensor has the following specs:
Construction - Thin switches are sealed in a durable vinyl cover and are designed for low voltage operation, Class II N.E.C. circuit operation, 100 watts at 24 volts AC or DC. Contacts are single pole, single throw, normally open, momentary contact type.
Sensitivity - Standard sensitivity is 7-10 lbs.
Lead Wires - COS leads are single 22 AWG 2-conductor wire.
I'm new to Arduino, have no direct electronics experience and need to develop this interface quickly (I can program in C). Can someone please direct me to tutorials/examples relevant to this device?
Thin switches are sealed in a durable vinyl cover and are designed for low voltage operation, Class II N.E.C. circuit operation, 100 watts at 24 volts AC or DC. Contacts are single pole, single throw, normally open, momentary contact type.
So I expect an +24V and a GND and a "data" -line. The dataline will be 0 or 24V. To change that to 5V you need a voltage divider, that divides in 5.
Furthemore you must connect the GND of teh sensor to the GND of the Arduino.
dataline (0/24V) ----[10 K] ------ X ------ [ 2.5K ] ----- GND ---- Arduino GND
The X should be connected to a digital pin;
Check - http://arduino.cc/en/Tutorial/ButtonStateChange - for some code to get started
Many thanks Rob. If I can test your patience a little... I've uploaded a jpeg of what I understand the circuit might look like. It may be completely wrong - but i hope it can act as a reference - please see:
Unfortunately I don't yet have the sensor (it's coming by post) - but when you say the sensor has a ground, I assume there must be a shield on the wire that leads from the sensor and this is the ground. Is this correct?
How far wrong is my circuit?
Actually, as I understand it, the recora chair mats just act as a switch. Those ratings are just maximum ratings (aka, don’t put more than 24V and x amount of current through it).
Because it acts as a switch, all you need is a pull up resistor and input pin. The microcontrollers generally have an internal pullup resistor, but either external or internal is fine. Attached is a rough picture of your schematic. When the switch is closed (someone on the sensor), the pin of the microcontroller will be 0V, and when the sensor is open (nobody on the sensor), the voltage on the pin of the microcontroller should be VCC (3 or 5V generally).
The advantage of an internal pullup resistor compared to an external is that you can turn power off to the device when you are not sensing (save power). If static current draw is not a factor, then either is fine.
Finally, I hear that for chair mats and bed mats, recora created a sister company called telehealth sensors. Maybe you can find more info at their site www.telehealthsensors.com
Hope this helps.
Thanks very much samr! A friend gave me much the same advice a couple of days ago. Will check out the telehealth site.