IR Rays are invisible to human eye, so it is very difficult to check the working of IR LED. Usually we use a Mobile camera to test IR LED since the pink light from the IR LED becomes visible in digital camera. We can make a simple IR LED tester so that, before using it in the project, we can confirm whether it is good or not. Lot of IR LEDs are also in our Junk box. So we can check all IR LEDs and discard the damaged ones. The same tester can be used to check all ordinary LEDs, Photo diodes, Silicon and Germanium diodes etc.
You can turn on a 3 Volt LED just using 1.5V Battery. It is the Joule thief circuit doing the trick. Joule thief circuit is a self oscillating voltage booster used to drive light loads like LED. The name Joule thief is given to the circuit because; it is stealing the Joule or energy from the battery. That means, it is extracting energy even from an almost dead battery to power a load. Try it. This is one basic circuit you should know as a starter in electronics.
You can use this Flashing LED light for Projects, Model vehicles, Toys etc. It blinks in a peculiar fashion with bursting flashes.
This Tiny circuit can protect your LCD TV from Voltage surge at power on. It takes 2 minutes delay before connecting power to the TV. Within that time, mains power will become stable. Heavy inrush current at power on or when power resumes after a power failure can damage the TV permanently. If few minutes delay is provided, the AC will become stable. This is the delay technique used in Stabilizers.
Usually we use a battery level indicator along with rechargeable battery to monitor the voltage level. If the Lead Acid battery is deeply discharged below a particular voltage level ,Memory effect develops and the battery never attains full charge later. So it is necessary to monitor the safe voltage level in the battery. A 12 volt Lead Acid battery shows 13.8 volts in fully charged condition and it should not deep discharge below 9 volts. If it happens, immediate charging is required to maintain the health of battery.
This is a simple but useful LED flasher that can be used as power on indicator or along with alarms. Simply you can use it as a Mock Alarm in the gate or door to baffle the intruders. Do this very simple circuit and it can be an evening project for you that take only 10 minutes to complete.