Controlling Lighting with Motion Sensors and SSR’s

In my never ending quest to save energy, I decided to connect Motion Sensors (more accurately “Passive Infra Red” or PIR) to an  Arduino, and having that control my lighting through an SSR. This is a good way to make sure the lights go out when people leave the room, and come on when they enter, preventing stumbling in the dark with your arms full trying to find the light switch.

Parts Needed:

Qty (2) 10k ohm resistors (Radio Shack 5 / $1.20)

Qty (1) SPDT Center Off Toggle Switch

Qty (1) PIR Sensor

Qty (1) SSR

Qty (1) Arduino

Full code and construction info at


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8 Responses to Controlling Lighting with Motion Sensors and SSR’s

  1. Russell says:

    What are the losses like for those SSRs? Do you need to heat-sink?
    I like the idea of using them to eliminate circuits not needed for emergency use when the grid goes down. They could also be used for timers to stagger big startup loads when the power comes back. Ie stop the pump, fridge and freezer trying to start at the same time.
    Might also be good for an automated isolation of the lister-gen if the voltage or freq dropped ( eg dumbass running out of fuel!)

  2. KK4HFJ says:

    At heavy load levels, just screw these to a metal backing plate with heat sink compound. I’m working on a load shedding project based on my watt meter board I designed.

  3. Harold says:

    I don’t know what your motion/infra red switch cost but if it’s much the pay back is going to take a very long time.

    While performing maintenance for the National Park Service I was directed by my supervisor to install a similar switch in the 14 offices of the maintenance office complex. It’s been a while so my memory of actual cost is probably not reliable but I believe it was in the neighborhood of $50 per unit. Because the motion switch replaced the wall switch by the door the area covered was not optimal. Ceiling mounted switches would have been better but both the cost of procurement and man hours to install was more.

    At about 8 cents per kilowatt hour that’s 625 kilowatt hours of “smart switch salvaged off time” to break even. Each office had two or three 4’ x 2 fluorescent fixtures. Assuming everyone left their lights on while eating lunch (30 minutes – 12 minutes delay time in the switch) out of the office plus another hour of out-of-office goof off time a day—well you do the math.

    So what happened? I observed several frustrated office workers flailing their arms around every 12 minutes (the delay programmed in the switch plus the IR part was very iffy) to get their lights back on. The budget lady finally gave up, raised the window blinds all the way up and turned the switch off. The chief of maintenance finally called me and said something to the effect of “Get this *@!!# switch out of my office and install a “real light switch!”

    My solution was “find a way to insure that when you say: ‘Turn the lights off when you leave the office whoever works there knows that you mean it’.”

    I hope your switch works better. The ones in the supply warehouse did but they were far more expensive.

  4. KK4HFJ says:

    The one listed is $13, but can be found for less. You can mount it any where you wish, and you can program the delay for whatever you wish. I included a manual over ride (you missed that part?) for times when you know the room will be busy.

    • Quinn says:

      I think the convenience of not having to reach for a switch is probably the primary benefit of such a device. Best suited to small rooms like storage rooms, bathrooms, hallways, where you don’t want/need lights on all the time and where you don’t want to have to reach for a switch when you’re carrying things. The obvious application is bathrooms. You can control the light and exhaust fan and ensure that after you shower the fan will stay on long enough to dry out the room and then shut off.

      • George B. says:

        How many of us have opened a closet to see a 60 watt bulb on.. and wondered, has it been on a week, or a month? At the same time.. I remember office space.. where it all went dark.. a whole room full of people not animated enough..

  5. Jetguy says:

    There are a couple of important aspects of this DIY version though.
    The first is learning how to both program it and the phsycial side of wiring it up. The more subtle aspect is that you can determine how complex the function is.
    The final aspect is, yes, if you buy retail components this can add up. For the first time user though, what you are really paying for is packaging and documentation and maybe even sample code in many cases. If you’re smart and been doing this a while, then once you have the prototype, you can part this thing down to about $15 a pop by using bulk components, digging out your own data sheets on surplus parts or just hacking broken thrown out junk by others. I should also point out the SSR is overkill. That’s fine for the test design and even OK if you really need it for the load or isolation reasons, otherwise a triac, relay or whever else you come up with may be the cheap solution. Also, this is the beauty of Arduino, so port than final code from a $4 chip to a $0.75 chip with only the required pins for a production version if your’ making a couple or “permanent” installations.

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