This causes the resistance of LDR to increase and the voltage at the base of the transistor ... The simple schematic diagram of a smoke detector presented here utilizes the gas sensor TGS 813 as the ...

In the video embedded below, he shows off a homemade voltage detector circuit that he constructed using a trio of BC547 NPN transistors. The circuit is pretty simple though very useful all the same.

For more infrared detectors check the list bellow. The infrared detector circuit can be easily wired on a small veroboard or any general-purpose printed circuit board. Pin configurations of IC LM386, ...