Here's one of the easiest, simplest and the most popular FM transmitter for amateurs and electronics beginners. With this DIY kit, you can transmit...
If you have to come to this page directly from a search site, please go to this article first. This is the second article...
Learn how to use UM66 or BT66
This works same as the other dark detector circuit. When light is falling on LDR, its low resistance drives transistor Q1-BC547 into conduction. This...
For the circuit to work as light operated musical bell, we need to connect the SW1- switch to N/C terminal of relay. LDR has to be kept in a dark case.
An automatic dark sensor can be made using a PNP transistor(BC557).
In this case, LDR has been replaced with capacitor C1-0.01uF and resistor R3-1K has been replaced with L1 & VC1. In place of a LED, a Piezo Diaphragm has been kept. We just need to add inductor, capacitor and a piezo diaphragm to convert a dark detector to an AM radio.
A breadboard is a device for testing temporary electronics projects. Components used to test a circuit can be reused for other projects. None of the components are damaged. Almost all people start to learn electronics using breadboard because it is the simplest way of making circuit. The photograph shows a typical small breadboard which is suitable for beginners building simple circuits with one or two ICs (chips).
The circuit is ready for testing. Connect battery terminals and see the output. As you block light falling on LDR(Light dependent resistor), the LED glows. OUTPUT: [youtube]http://www.youtube.com/watch?v=qmWAgoHwy3w[/youtube] THIS CIRCUIT IS EXTREMELY SENSITIVE TO DARKNESS. EXPERIMENT THE CIRCUIT IN A HIGHLY ILLUMINATED ROOM. LED GLOWS EVEN IN LESS DARKNESS. Use torch light if the LED glows in less darkness. You can adjust the sensitivity of the circuit using a variable resistor in place of R3-300Ohm. Try this circuit with other resistances as well, for example, 1K, 10K and 100K, etc.