| RSS Web Feed for Renewable Energy UK |  | REUK Shop | Directory | About Us  

PIR Sensors



PIR Sensors

Find out how to integrate PIR (passive infra red) sensors into renewable energy applications

electronics | solar | general
  Printer Friendly Version Print Article     

A Passive Infra-Red (PIR) sensor is an electronic device commonly used in security lighting, and burglar alarm systems. A PIR sensor is a motion detector which detects the heat (infrared) emitted naturally by humans and animals. When a person in the field of vision of the sensor moves, the sensor detects a sudden change in infrared energy and the sensor is triggered (activated).

Passive Infrared Detectors


Fresnel Lens on the front of a typical PIR sensor

At the front of a PIR sensor unit is a fresnel lens (pictured above). This special kind of lens is used to gather light from a very wide field of view and focus it directly onto a passive infrared sensor (as shown below).

PIR sensor

Some electronics inside the PIR sensor unit then decide whether the infrared light detected is from a warm moving body, and if so, triggers a switch.

Uses for PIR Sensors


PIR sensor with integrated spotlight
The commonest use for a PIR sensor is automatic security lighting. Whenever a suitably large (and therefore probably human) warm body moves in the field of view of the sensor, a floodlight is switched on automatically and left on for a fixed period of time - typically 30-90 seconds *. This can be used to deter burglars as well as providing lighting when you arrive home at night.
* The duration the light is left on for can usually be set by the user.

Such PIR security lighting systems are available from a wide range of sources from as little as £10.00 up in the UK.

PIR Sensors and Renewable Energy

The vast majority of commercial PIR sensor products are built to run on 240 VAC mains electricity. This makes them unsuitable for most renewable energy powered systems such as motion activated CCTV systems in remote locations. Although a power inverter can be connected to the RE system battery bank to obtain the necessary voltage, using it for 24 hours per day for such as small load would be a huge waste of energy.
12 Volt DC powered PIR sensor

Fortunately 12 Volt DC powered PIR sensor units are available. These (such as this 12V PIR sensor available in our REUK Shop and pictured above) can be connected directly to a 12V battery or battery bank, and used to trigger a Relay when motion is detected. The relay will switch on/off a light or any other 12VDC or even 240VAC device if required.

If a power inverter is necessary to power a 240 Volt device switched on by the PIR sensor, then the inverter can also be turned on as and when required rather than needing to leave it on 24 hours per day. This saves a considerable amount of energy.

This PIR sensor will run off 10-14 Volts DC electricity and draws a current of under 10mA.

PIR Sensor Timer Circuit

12 Volt PIR Sensors do not usually include a built-in timer. Therefore, it is necessary to put together a very simple circuit so that whatever device is connected to the PIR sensor will stay switched on for the desired length of time.

PIR sensor timer circuit - turn on a device and leave it on for a time determined by the values of C and R

The circuit shown above will turn on a floodlight or other device for a time in seconds approximated by the value of the capacitor C (meaured in microFarads) multiplied by the resistor R (measured in megaOhms) multiplied by 0.75.

For example, if R = 1M and C = 22uF, the floodlight would remain lit for around 16 seconds after the PIR sensor switched off.

Full details and plans for PIR Sensor Circuits are now available by clicking here. We also have complete PIR Relay Timers available now in the REUK Shop.

NEW An alternative type of PIR sensor module is now presented here: KC7783R PIR Module, better suited to many standalone motion detecting designs than the burglar alarm type PIR sensor discussed above.

Weaknesses of PIR sensors

In order for a PIR sensor to work well most of the time, they are designed with certain limitations. A PIR sensor cannot detect a stationary or very slowly moving body - if the sensor was set to the required sensitivity, it would be activated by the cooling of a nearby wall in the evening, or by very small animals. Similarly, if someone walks straight towards a PIR sensor, it will not detect them until they are very close by.

PIR sensors are temperature sensitive - they work optimally at ambient air temperatures of around 15-20 degrees Celcius. If the temperature is over 30 degrees, the field of view narrows and the sensor will be less sensitive. Alternatively, if the temperature is below 15 degrees, the field of view widens and smaller or more distant objects will activate the sensor.



Article Last Modified: 14:16, 18th Aug 2010

Comment on this Article

If you have any comments on this article, please email them to neil@reuk.co.uk.

I read this article on your website. I also bought one of these timers and followed your instructions (Convert Digital Mains Timer to Low Voltage).


External use PIR motion sensor converted to 12VDC


Using the info I learned from the timer, I converted one of these (pictured above) for 12V use ES34 External PIR Light Controller.

We've been using this particular make of PIR for years and they are long lasting and 180 degrees. The conversion is just the same as you did with the timer. Using this PIR instead of the Honeywell IS-215T means that you still get to use the PIR onboard timer and photocell as normal. I'm just a hobbyist so my knowledge is limited, but as the rectifier in the PIR has 22v Zeners, it's likely that it will work with 24v as well. I did test it at 36v and 24v and it worked. It's currently been working away fine on 12v for about a month now.

I use it to trigger CCTV recording. I did use the Honeywell (good choice on your part – we've been using them for over 10 years on out Alarm Systems, with only one failure). I used a Honeywell initially for external use but found it to be not quite sensitive enough and sometimes didn't trip. I think the Honeywell is less sensitive in order to minimise false alarms. False triggering an external light isn't so much of a nuisance so I think that these external PIR's are more sensitive.

Dave (Hadden Alarms)
December 15th 2011


Recommended Related Articles

People who read this article also enjoyed the following articles:

PIR Sensor Circuits
Find out more about using PIR sensors within renewable energy applications
Article Last Modified: 11:32, 3rd Nov 2007
electronics | electric circuit | general | solar

Multiple PIR Sensor Circuits
Connecting more than one PIR sensors in a circuit
Article Last Modified: 17:00, 9th Mar 2009
electronics | electric circuit | general

Motion Sensor Light Switch
Fit a motion sensor light switch to automatically switch off lights when a room is empty
Article Last Modified: 11:00, 16th Mar 2011
lighting | energy efficiency | shopping

KC7783R PIR Module
Find out more about the economical and easy to use KC7783R PIR motion sensor module
Article Last Modified: 15:40, 30th Nov 2011
electronics | electric circuit | general | shopping

Relays and Renewable Energy
Find out more about relays and their uses in renewable energy applications
Article Last Modified: 12:33, 14th Aug 2010
electric circuit | electronics | general

LM741 Light Dark Sensor Circuit
Build a light/dark sensing circuit to automatically turn on/off lights and other devices
Article Last Modified: 08:43, 2nd Nov 2007
electronics | electric circuit | general

Timer Circuits With 4060B
Build a reliable timer to switch devices on and off - from 30 seconds to 24 hours
Article Last Modified: 08:58, 15th Aug 2009
electronics | electric circuit

Water Heating with Surplus Solar PV
Heat water with surplus solar generated electricity
Article Last Modified: 19:38, 20th Oct 2011
solar | water | general

DIY Solar Water Heating Prototype
Follow the construction of a successful DIY solar water heating prototype
Article Last Modified: 14:16, 19th Aug 2008
solar | heating | water

LED Dimmer Circuit
Find out how to put together a simple but efficient PWM dimmer circuit for LEDs
Article Last Modified: 09:42, 16th Mar 2011
lighting | electronics | electric circuit

© 2006-2012 REUK - All Rights Reserved
Page Last Updated on 31st January 2012 at 01:50:15pm

Latest
Articles


Make a Still
Find out how to make your own still for distilling ethanol fuel
biomass
13:49, 31st Jan 2012

UK Feed in Tariff to be Cut by 50 Percent
UK government announces 50% cut in feed in tariff payable on new solar PV installations
solar
13:20, 30th Jan 2012

PICAXE Microcontrollers
Find out about PICAXE microcontrollers and their use in renewable energy projects
electronics
13:12, 30th Jan 2012

Make a PICAXE Repeating Timer
Make your own repeating timer with our automatic PICAXE Basic code generator
education
12:42, 30th Jan 2012

Rainbow Power 300W Hydro Generator
300 Watt 12/24 Volt hydro power generators from Rainbow Power
hydro
12:44, 27th Jan 2012

Solar Tracker
Set up solar panels to track the motion of the sun across the sky to maximise power output
solar
10:46, 27th Jan 2012

Light Dark Dawn Dusk Relay Controller
Find out about the REUK Super LDR light/dark dawn/dusk relay controller
electric circuit
16:48, 24th Jan 2012

Karasouli SCC 20 Wind Turbine Charge Controller
Find out more about the SCC-20 wind turbine charge controller and dump load controller
wind
12:46, 20th Jan 2012



REUK Shop

Popular Items


REUK SUPER LDR DUSK DAWN RELAY CONTROLLER
Multi-function light detector triggered light/dark dawn/dusk relay controller
£18.95 each.
Complete Circuits



KARASOULI SCC 20 CHARGE CONTROLLER
20A rated wind turbine charge controller and dump load controller with blocking diode and heatsink
£43.95 each.
Renewable Energy System Parts



SOLAR PUMP CONTROLLER WITH RELAY
Solar water heating system microprocessor controlled circuit with fitted 10A relay
£25.99 each.
Complete Circuits



REUK SUPER POULTRY LIGHTING CONTROLLER
Control up to 8 Watts of LED spotlights to stimulate egg production in birds
£29.99 each.
Complete Circuits



REUK SUPER TIMER 2
User programmable 12VDC powered 16A rated repeating relay timer. 1 second to 99 hours ON and OFF times
£23.99 each.
Complete Circuits



300 WATT POWER INVERTER
Convert 12V DC battery power into 230 AC to power portable televisions, computers, video recorders etc. 300 Watt power rating - peak power 600 Watts
£29.99 each.
Renewable Energy System Parts



CONVERTED PROGRAMMABLE DIGITAL TIMER RELAY
Mains powered programmable timer converted to low voltage with relay board
£21.99 each.
Renewable Energy System Parts



12 VOLT REGULATOR
Supply a fixed 12.0 Volt DC to your devices (up to 1 Amp output)
£4.99 each.
Complete Circuits



MR16 CERAMIC BULB HOLDER
Bulb holder for 12 Volt LED spotlight bulbs
£1.39 each.
Energy Efficient Lighting