Webcam Sight Illuminator Circuit
Setting up a webcam sight illuminator over your laptop’s webcam will certainly “enlighten” your online conversations. This compact clip-on light improves the quality of webcam photos and videos in low-light situations, and has been designed for placement directly over and around your laptop’s webcam. It operates via a USB port, incorporates a white-light LED, and detects low-light levels automatically.
Circuit Description
A standard 5-mm photoresistor (LDR) detects the ambient light level, and its resistance drops when sufficiently illuminated. The resulting voltage level on one input of the single comparator LM311N (IC1) cuts off the reed relay (RL1) that is connected to the comparator’s output to keep the 1-W white-light LED (LED1) in the off state. When the LDR is not sufficiently illuminated, the output state of IC1 is reversed, thereby energizing the relay so that the LED connected to it is lit. The switching level can be adjusted with the 10-K multi-turn potentiometer (P1). The component values are not especially critical; however, the coil of the relay must have a very low operating current (no more than a few mA).
Advanced current regulator AMC7135 (IC2) is used to drive the white-light LED (3.6 V/1 W). The AMC7135, available in SOT-89 and TO-252 packages, is a low-dropout current regulator rated for 350-mA constant sink current. The driver consists of the electronics that take power from the input supply and send it to the LED. Constrained to a particular current, the LED will settle in at its forward voltage (VF) for that current and the rest of the voltage from the input supply will be handled by the driver chip. If the AMC7135 chip and LED are located in separate circuit boards (not recommended), the value of the 100-nF buffer capacitor (C2) should be increased to 1uF. For more information, refer to the official datasheet for AMC7135, published by ADDtek Corp.
(Current consumption of the finished circuit when powered from a laptop USB port — 360mA.)
Circuit Construction
The entire circuitry can be built using nearly any technique you wish. Mine was built on a small universal SMD prototyping board. Component layout is not very critical, except that the 100-nF buffer capacitor (C2) should be very close to the AMC7135 (IC2). Double-check your work, especially the power connector and IC1/IC2 pins, as simple mistakes can destroy the chips and ruin your day. After construction, enclose the finished circuit in an attractive donut-shaped ABS/Plasticized Rubber case with a suitable light diffuser in front of the white-light LED. The finished system is a small and easy-to-use portable LED light, which can be used for interior and exterior applications where a standard USB port is available. For example, you can use this as a reading light if powered from a smartphone power bank/USB mobile phone charger.
However, as described earlier, try to use a suitable light diffuser with the power white light source for more effective protection of your eyesight!
Lab Note
- Prototype was first tested with LM311N (DIP-8) and later replaced with LM 311M (SOP-8).
- SOT-89 package of AMC7135 (AMC7135PKF) was used in the prototype. However, other popular packages can be used without any problem.
- It would be better to add a 100-K resistor from pin 7 to pin 2 of IC1 (LM311) to provide a positive feedback. When the output goes low, the threshold is reduced a little, and when it goes high, the threshold is raised a little. These changes are opposite in direction to the change in the voltage at pin 3 that produced them, so they furnish a snap action to the comparator, called the hysteresis. With the 5-V supply input (and P1 at its center position) this modification gives a difference of 0.25 V (the threshold for the output to go high to low is 0.25 V higher than the threshold to return from low to high).
Parts List
(Webcam sight illuminator in action – representative image.)
Another Application
