Introduction: Ultrasonic Nightlight

A project that can be done over a weekend, for making a high brightness LED night light, that is activated by an ultrasonic sensor, with battery backup based on a joule thief circuit.

Full details of the build are given here as I step through the design and construction.

See my website for schematics, firmware etc:

Project Features:

1. the night light uses a high brightness white LED, that is triggered by tripping a ultrasonic beam

2. a single toggle button being pressed down, sets the LED on time, in steps of one minute up to five minutes (the number of flashes equals the selected time)

3. the ultrasonic sensor sensitivity is similarly set, in steps of 25cm up to greater than 1.5m by the toggle button

4. the 3D-printed enclosure, allows changing rotation and elevation of the sensor and LED

5. the light sensor, only enables LED power-on during night time, i.e., the preset darkness level

6. 5V power is provided via a standard phone charger

7. in event of mains power outage, the white LED is automatically powered-on via the joule-thief circuit using by a single AA battery


Here are the items that you will need for the project:
1. the LED light circuit is based on the joule thief design, you can make this using the ""dead bug" style to avoid needing a printed circuit board, but I used veroboard in this project

2. a NPN transistor, ferrite toroid for winding the coil and a couple of resistors, all items that can be easily bought, or salvaged from disused electronics, I'll show you how to salvage the needed parts like the toroid from a broken CFL light globe. 2. a high power 1W white LED or similar

3. a HC-SR04 ultrasonic sensor module - a couple of dollars from ebay

4. a Attiny85 digispark - again, a couple of dollars from ebay, the micro-usb version has advantages as enables power from a phone charger

5. A light dependent resistor as a light sensor, so the ultrasonic sensor will only trip on at nighttime

6. a couple of buttons , and

7. a suitable enclosure or housing to mount the components - I designed a customs housing that has a rotating mount for the sensor and LED, but this can be anything suitable for your exact purpose depending on your imagination and materials.