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What type of circuit is this???

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rtm038

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Hello,
A buddy of mine is a mechanic and has a "Snap-On" brand LED rechargeable flashlight/work light. To turn the light “On” and “Off”, the user presses a momentary pushbutton switch that passes a solid piece of plastic between 2 sensors with each push. Also, if the light is "On" when the battery is removed, the light turns “Off” and remains off, even when the battery is reinstalled, until the switch is pushed again. What type of circuit is this and how does it work?

Thanks
Ryan
 
Sounds like a simple state machine to me. I've seen a few flashlights like this, sometimes they also have a "blink" mode where the light blinks.

The on/off function (with no blink) could be done with just a simple j/k flip flop. with both J and K inputs tied to power and the momentary button connected to the clock input. When you push the button, it simply flips the state of the flip-flop; so if its off, it turns on and if its on it turns off. When you power cycle it, the flip flop should come initialize to the "off" position automatically (although it may not if you power cycled it really quickly).

To add more states like the blink function, you'd need another flip-flop and maybe a 555 timer circuit. With two flip-flops you could have four states, so one state would be wasted.
 
Stellarcore said:
Sounds like a simple state machine to me. I've seen a few flashlights like this, sometimes they also have a "blink" mode where the light blinks.

The on/off function (with no blink) could be done with just a simple j/k flip flop. with both J and K inputs tied to power and the momentary button connected to the clock input. When you push the button, it simply flips the state of the flip-flop; so if its off, it turns on and if its on it turns off. When you power cycle it, the flip flop should come initialize to the "off" position automatically (although it may not if you power cycled it really quickly).

To add more states like the blink function, you'd need another flip-flop and maybe a 555 timer circuit. With two flip-flops you could have four states, so one state would be wasted.

no no .. this sounds mechanical in nature. A flip flop cannot keep the last known state after power ahs been removed. Besides, I dont think low cost flash lights can affor things like flip flops and other digital stuff. Cheap mechanical is the way to go.
 
The important bit in the OPs text was

Also, if the light is "On" when the battery is removed, the light turns “Off” and remains off, even when the battery is reinstalled, until the switch is pushed again.
The light always starts in the off state when a battery is installed. It does not remember the state when the battery is pulled.

Unless things have changed "Snap-On" is not cheap.
 
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It could be using a slotted opto-sensor like the type used by floppy drives or mice.
The solid piece of plastic breaks the beam when pressed and toggles the state.

This would be very durable but would mean a small constant drain on the battery even when switched-off.
I suspect these being a more expensive flashlight, they use a higher capacity battery that could easily cope with wasting a few milliamps for months.
 
picasm said:
It could be using a slotted opto-sensor like the type used by floppy drives or mice.
The solid piece of plastic breaks the beam when pressed and toggles the state.

This would be very durable but would mean a small constant drain on the battery even when switched-off.
I suspect these being a more expensive flashlight, they use a higher capacity battery that could easily cope with wasting a few milliamps for months.

Is this type of circuit easy to build?
 
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