Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Simply look at the datasheet of a 9V alkaline battery on Energizer's website.
If the resistor is 3.3k and the LED is a 1.8V red one then the current with a brand new battery is 2.2mA (fairly dim) and the datasheet says the battery voltage will slowly drop which will dim the LED and it will be extremely dim in about 720 hours (one month).
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