Category: Electronic Gadgets

Lights On! (part 2)


Hi there!
It is summer, and I have a number of upgrades in mind for my outdoor living areas: some involving electric upgrades, some involving gardening, some involving landscaping.
One thing I have in mind involves the night illumination of the gazebo and its surroundings. The current illumination is based on low power LED strings, powered by batteries recharged during the day by small solar panels.

However, I found that this kind of illumination has a lot of drawbacks. First of all, the lights are very dim. They are just fine when entertaining guests having conversations while enjoining the freshness of the evening air. But when it comes the time to do some table game that requires being able to look at pictures or reading stuff, often we end up going inside where we can have more light.
In addition, I need to turn on and off the lights manually, whenever I need them. If I leave them always on and let their sensors take care of the switching, they end up using the whole battery by the middle of the night and, sometimes, they take so long to recharge that by the time it is evening they don’t last that much anymore.
The solution would be to use bigger solar panes, but the batteries are still small and they also need their time to recharge. If I let them recharge too fast, they will start loosing their capability of retaining the charge too soon, and I would have to replace them relatively often. So I would trade off the usage of solar panels with more waste in exhausted batteries.

The right thigh to do, in my view, is therefore to use regular 120V lamps, obviously low power LED, but brighter than the ones I currently have. The thing is that I do like the automatism of having them turn on and off automatically from dusk to dawn. So, I thought I could design and build my own dusk to down automatic switch, which actually require just very few component and it is very cheap to make.

Schematic


Above is the schematic of my dusk-dawn automatic switch. It is a very standard design, and it requires just a few components.
The load is basically made of the LED lamps we want to control.
The 120Vac input goes directly through a protection fuse and to the series of a 50K resistor and a photo-resistor which is the sensor that will detect the daylight condition to turn the light bulbs on and off.

When there is enough daylight, the resistance of the photo-resistor is very low, in the range between 1K and 4K. When we are getting closer to dusk, the daylight starts dimming and the resistance instead increases. Once the resistance hits the 16K threshold, the voltage at its leads goes above 30Vac.

It is at this point that the DIAC starts conducting and it triggers the TRIAC. The TRIAC, in turn, will let the current flow through the load, thus turning on the lights.
Very simple right?

Lights On!

Hi there!

It sometimes happens that we build something out of necessity, to help us with little day-to-day tasks, and this is the case for today’s project.

The boiler’s room in my basement is a very cramped place that I need to access frequently because I keep in there a freezer for groceries. It turns out that I often have my hands full when I come back from taking something from the freezer, and it is difficult to reach for the light switch.

To obviate to this problem, I decided to build an automatic light switch, so I don’t have to maneuver it manually anymore. And, since I was at that, I decided to make one that not just turns off when I leave the room, but also turns on the light automatically when I enter the room.


The core of this device, technically called an Occupancy Sensor, is a PIR, or Passive Infrared sensor. I have a version of it called HC-SR501 that puts together a Pyroelectric Infrared Detector, or PID, with a bunch of other electronic components that make the sensor useable with very few external components. The PID is concealed underneath that white little dome, which is nothing more than a Fresnel lens that concentrates the light on the actual sensor, thus increasing its sensitivity.


The PID used in this device is called LHI 778, and is capable of detecting infrared emissions over a background noise of up to 85 degrees Celsius. You can see from its data sheet that it is like a small metallic cylinder with 4 pins coming out of it. This PID actually contains two infrared sensors connected in series, to increase its sensitivity.

This one is the schematic I made to use the PIR motion detector. The Detector is connected through the pin header J1 on the left. The header provides the power supply for the detector on pins 1 and 3, and captures the output signal on pin 2.

The signal from the detector goes to the base of transistor Q1 which pilots a relay that is used to control the lights of the room where the device is located.

The 5V power supply for the transistor and the relay comes from an old USB charger, so I didn’t have to build a power supply just for this application. LED1 and R1 provide a visual indication that tells us when the gadget is turned on.

The actual power supply for the whole thing comes directly from a 120V socket, goes through a 1A fuse, and through a power switch.

When the switch is set to on, both the USB charger and the common terminal of the relay receive the 120V. Power socket J3 receives the 120V only when the switch is on and, simultaneously, the PIR detects the presence of a person.

The following archive contains all the files you will need if you decided to build this device for yourself, and more.

lights_onDownload

You can also watch this video for further details on the construction of this device.

Important note: this device involves the use of potentially deadly voltages and you should not try to replicate it if you have no experience with high voltages. Build it at your own risk.