Accurately soldering parts, especially ones of the smaller SMD variety, requires both adequate lighting and magnification in order to be done without smearing solder or incorrectly placing a component onto the wrong pad. Element14 Presents host Katie Dumont uses a specialized headband that has a built-in light on top and a pair of magnifying glasses on the front for hands-free use for whenever she is soldering at her workbench. However, the always-on nature of the light means she must manually switch it off any time she needs to read something on her computer monitor due to the immense glare. Her proposed solution to this problem involves using some kind of sensor to toggle the light depending on the current conditions.
Dumont's first idea was to take a simple tilt switch sensor and use it to detect if the headband has been moved downwards, thus turning on the light and turning it back off when the tilt switch is open. However, she also wanted to have the light on when looking at things from any angle, so her revised design swapped out the tilt switch for a more complicated lidar-based solution.
In this newer design, a SAMD21G18 microcontroller constantly checks the current range reported by a laser-based VL53L0X time-of-flight (ToF) module. If the distance falls below a predefined threshold, a MOSFET is activated, which allows current to pass from the battery through the bright white LEDs and to ground. Likewise, the inverse occurs when the distance sensed by the VL53L0X is above the threshold. Once the hardware and software had been figured out, Dumont soldered all of the components onto a single piece of perfboard and attached the whole assembly to the top of the headband.
Although the design worked fine on a breadboard, the move to the perfboard and headband LEDs introduced a very strange problem, as the LEDs would rapidly flicker while on. Dumont started debugging the issue by looking at her oscilloscope to check the timing and voltages of the LEDs. Her first thought was that the ToF sensor was pulling too much power while being read, thus causing a small dimming effect for around 100ms. However, adding a capacitor across the power lines did not solve the problem, meaning the power management circuitry of the headband itself was a more probable cause.
To see more about this project, you can watch Dumon't build log video here on YouTube.