Have you ever walked into a dark room in the night and wanted to navigate without turning on the ceiling light. Perhaps, just to check on the kids without waking them. We all know the uncomfortable feeling of turning on a bright light in a room when are eyes are accustom to the dark. A dim night light is the solution to easy room navigation. You can purchase off the shelf night lights or in my case built my own custom nightlight. I chose a cute figurine character that my kids might like to have light up. There are so many night light possibilities to choose from.
This instructable will give you the information to build the circuitry you need to make your own custom night light. PCB making and soldering skills required.
Step 1: Picking What Device You Want to Make Into a Night Light.
Choose a device/toy that you would like to make into a night light. It is important to choose a device that is hollow and made of a plastic or other material that will allow light to pass through it. Think about how to disassemble the figurine without busting it and how it can be wired with LED's. Some common figurines have screws and glue holding them together so disassembly may be difficult.
Shine an LED through the plastic to test it. If little light will pass through the material the night light will be useless. I have made three night lights for my kids so far. I have used a Hello Kitty shampoo bottle, a Lego lighthouse and a McDonald's restaurant Happy Meal Minion toy. Consider the base and how you want to power the nightlight. I started powering the night lights with three AA battery packs. This gave good portability however I was changing batteries every three to four months. I now use a 5 volt wall wart for power. These are quite common and you probably have an extra one lying around the house. Cell phone chargers are a common source.
I started making my night light using Stuart the one eyed minion then decided to switch minions and go with Tim the two eyed minion. Not positive on the names of the minions. You can correct me if you want.
Step 2: Design the Circuitry.
Well, I have completed this task for you. I have included in this instructable the electronic schematic and PCB layout if you are interested in using them.
Just a little history. My first night light used a Air Wick motion sensor hack (https://www.instructables.com/id/Re-purposing-an-Air-Wick-Freshmatic-Compact-i-Moti/step3/Approach-1-Digitized-Sensor-Output-Simplest-way/) with discrete integrated circuits (AND gates etc.). My second night light used a Picaxe microcontroller with a purchased motion detector. This instructable uses a purchased motion detector and simple circuitry. Be prepared, this instructable will involve making a PCB and soldering electronic components to it.
Attached are two files. One file is the schematic and the other is the PCB layout of the night light circuitry. Both files were generated using the free software program called PCB express. I have included both files as a PDF as well.
The explanation of the circuitry.
The PIR (passive infrared) or motion sensor comes as a completed PCB. Add power and ground to this module and it will output a 3.3 volt signal when it detects motion. This output signal will "turn on" a transistor (BJT) and allow the 5 volt power supply to send current through the transistor. The capacitor is charged and the mosfet is "turned on" by 5 volts being applied to its gate. Turning on the mosfet will allow current to travel through the LED's lighting them up. When the PIR output stops (no motion) the BJT "turns off" and for a short time the capacitor releases its charge (holding the mosfet "turned on") until its charge has dissipated through the 100K resistor. At a certain point the voltage at the mosfet gate falls to a point when the mosfet gets "turned off" and the LEDs fade out. There is an option to solder on an LDR (light dependent resistor or photo resistor) to the PIR board. This will restrict the PIR to outputting only when the lighting is low. This is more important if you are conserving battery power. I have soldered on the LDR to my nightlight.
If the PIR motion sensor is continually triggered (by constant movement in is line of sight) the LED's will remain on until the motion stops and the capacitor can discharge.
Here is a link to a PDF that has the PIR sensor circuitry: https://www.mpja.com/download/31227sc.pdf
Remove the white dome over the sensor. This dome helps with the motion detection but it is not necessary for the detection to work.
Step 3: Making the Circuitry.
I made my PCB from copper cladding board. The circuit was etched and holes drilled in for component attachment. The layout was printed onto paper from a laser printer and transferred to the copper board. All components I used for this device were scavenged from other electronics except for the motion sensor. I purchased it from here: (http://store.qkits.com/pir-infrared-motion-sensor-hc-sr501-pir.html). The components were soldered on the PCB and then assembled into the base. There are many instructables existing on how to make PCBs. Explaining how to do that is not the scope of this instructable.
Step 4: Assembling the Night Light.
I used a 4 inch ABS end cap as the base. It can be purchased at any of the hardware box stores (Home Depot etc.) from the plumbing department. A hole for the PIR sensor, power cord and the LDR are required. Also a hole on the top to feed the LED wires into the figurine is required. I use soft foam as a base. It is easy to insert and remove and holds the electronics from moving inside the base. The PIR PCB, LDR sensor and wires can be secured with glue from a hot glue gun. Glue the minion to the top of the end cap and you are done.
I thought this was going to be a cute night light. My initial concern was that my kids would fight over who would get the night light in their room forcing me to make two similar night lights to keep the peace. It turns out my son thought it was too creepy and unplugged the night light and left it out in the hall. My daughter didn't like that Tim was "staring" at her when she changed in her room. At least my wife thought it was cool, I guess it will end up in our room. Lesson learned, don't assume, ask my kids what they want, first.