EDIT - Sorry, I meant to post this is the Projects forum - MOD's please move if necessary.
Hi all, new to the forum (and electronic circuits) and would really appreciate some help. It's a really basic project but I'm sure I must have the maths wrong somewhere.
I have an alarm system which does not have a constant flashing LED on the bell box and am wanting to add one.
Length of battery life is my primary concern, but the most I can fit in the bell box is 2x AA's. So, I have a 6000mcd "ultra bright" flashing (approx. 1.5Hz) red LED (20Ma typical, 1.8v - 2.4v forward voltage) running off 2x Panasonic Evolta AA's (so 3v and circa 5200mah total).
So, after reading up, resistors are the easiest way to go for battery life. The only resistors I currently have are a 1k and a 10k from another project kit, so I soldered them both onto the positive line in series, not expecting the LED to light - however, it does! It's MUCH dimmer than normal but is night time visible at 20 feet which is fine. According to my maths the resistors limit the current to around 0.1Ma which is why I am confused - from what I've read around the net, LED's don't generally light below about 1Ma. And further calculations reveal that the batteries will possibly last up to almost 3 years which I find difficult to believe.
Is all of this possible?
And apologies for the long post but there's hopefully enough information for help.
Hi all, new to the forum (and electronic circuits) and would really appreciate some help. It's a really basic project but I'm sure I must have the maths wrong somewhere.
I have an alarm system which does not have a constant flashing LED on the bell box and am wanting to add one.
Length of battery life is my primary concern, but the most I can fit in the bell box is 2x AA's. So, I have a 6000mcd "ultra bright" flashing (approx. 1.5Hz) red LED (20Ma typical, 1.8v - 2.4v forward voltage) running off 2x Panasonic Evolta AA's (so 3v and circa 5200mah total).
So, after reading up, resistors are the easiest way to go for battery life. The only resistors I currently have are a 1k and a 10k from another project kit, so I soldered them both onto the positive line in series, not expecting the LED to light - however, it does! It's MUCH dimmer than normal but is night time visible at 20 feet which is fine. According to my maths the resistors limit the current to around 0.1Ma which is why I am confused - from what I've read around the net, LED's don't generally light below about 1Ma. And further calculations reveal that the batteries will possibly last up to almost 3 years which I find difficult to believe.
Is all of this possible?
And apologies for the long post but there's hopefully enough information for help.
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