Nighttime photography, and especially astrophotography, requires very long exposure. To get a good picture of the stars, you might leave the shutter open for several minutes. That gives nature plenty of time to produce dew on your lens, which can ruin the photo. The solution is a lens heater, but running that heater all night can consume a lot of power. That’s why Andrew Brocklesby built this automated lens heater that only activates when necessary.

Heated dew straps are common and affordable pieces of equipment for photographers. They slip over the frame of the lens and use electrical resistance to produce heat. Like the rear defroster on your car, that heat helps get rid of the condensation that forms as humid air comes into contact with a cool surface. Brocklesby’s device takes into account that the condensation doesn’t form unless both the ambient temperature and humidity are at specific levels. If they aren’t, then there is no need to activate the lens heater and waste power.

This device contains an Arduino Nano board, an SHT31 temperature and humidity sensor, and an OLED screen. Those mount onto a custom PCB that handles the connections and power distribution. Through the SHT31 sensor, the Nano can monitor ambient temperature and humidity. When they reach a level conducive to condensation, the Nano activates an off-the-shelf USB dew strap via a MOSFET. The OLED screen displays information about current conditions. All of those components fit into a tidy 3D-printed enclosure that Brocklesby can connect to a power source like a USB power bank or his car’s 12V outlet.

As you can see in his example images, this device helped Brocklesby capture some extraordinary photos.