Welcome home – ultrasonic sensor light

When you pull into the garage after a late shift, or evening out, Tiki Marama is there to guide you safely through the dark.

In addition to the idle washing basket or strewn kids bikes, we can get anything from huntsman spiders to cane toads to snakes lying around in our garage. This made arriving home at night (and fumbling in the dark from the car to the light switch) a bit of an unpleasant and risky experience.

After struggling to get an off-the-shelf security light (PIR sensor-based) to work reliably, I built my Tiki Marama.

Features

• Light turns on when object (car) comes within a distance threshold.
• Light stays on for 5 mins.
• Light won’t come on again until the object (car) leaves and returns again (ie has moved away beyond the threshold, then come within the threshold again).
• Adjustable distance threshold.
• Operates only between set hours (i.e. night).

Components

• AT Tiny 85 microcontroller
• Real time clock module
• Ultrasonic sensor module
• 2x usb sockets
• 10k linear potentiometer
• diode
• Pn222a transistor (used as a light switch)
• 330 ohm resistor
• Led desk lamp, usb (5V, 2W)
• USB cable, male-male and wall adapter

Learnings

• Initially I tried using a photo resistor to determine when it was night time. Seemed unreliable to calibrate. Swayed towards using RTC, since I hadn’t used one before and wanted to try it.
• Pointing the US sensor toward the car windscreen seemed to give very unreliable/ incorrect readings. Pointing at the side of the car worked much better.
• I did consider modelling some of the wooden parts in fusion 360, and milling them, as a way of refining the design and getting it accurate. Instead I just started making it and figured out the details as I went, using hardware I found lying around for inspiration/constraints. Build to think, and didn’t overcook it. It came together much more quickly than if I would have modelled it.
• First thought was to paint the totem face. While shaking the paint I decided to use coloured pencils instead, which was much quicker and has a nicer texture. And the plywood offcuts already had a coat of black paint.
• Perf board is flexible, but perhaps strip board would require less soldering (fewer jumpers) if components were well laid-out.