Re: Turning a light on and off with momentary switch

From: Harold Ryan (hryan_at_chartermi.net)
Date: 02/19/05 

Date: Fri, 18 Feb 2005 22:42:06 -0500

Hi Chris:

The circuit that you want to build consists of three sections. (1) The
momentary switch must be connected to a debounce circuit. This will create
only one edge when the switch is closed or opened. This is accomplished by
using a resistor and a cap to create a lowpass filter and a buffer logic
device like a 'AND' gate. The secret is to use an additional feed back
resistor that creates hysteresis.

The second section is the flip-flop that is wired to toggle. U can use a
74HC74 D type flip-flop or even a JK flip flop. The 3rd section is the
decode logic. If you want to just toggle an LED then there is no decode
logic. Just connect the output of the flip-flop to an LED or thru an
additional buffer chip. If you want to have 3 LEDS to sequence, just add
another flip-flop and use a couple NAND gates to decode the two outputs of
the two flip flops to generate 3 outputs. Use 74HCXXXX chips because the
crossover threshold voltage is 5volts/2 or 2.5 volts.

Harold

"Chris W" <1qazse4@cox.net> wrote in message
news:2OOQd.63983$jn.59042@lakeread06...
>I want a circuit that will turn a light on with the press of a momentary
>switch and then turn it back off when the momentary switch is hit again. I
>had heard that a flip flop might be the way to go. After some reading, I
>have found that a flip flop is a much more complex device than I was lead
>to believe. I think a flip flop would some how do the job, but it is going
>to take some more reading before I figure out how. If you have been
>reading some of my other posts, you know that I want to turn on and off
>more than one light, so I need several of these circuits, preferably using
>the minimum number of components.
> Another option I would like to explore is to turn the light on and off
> using 2 inputs. Say we have in put A and B. If input B is high, when
> input A goes high, turn the light on, or leave it on. If input B is low,
> when input A goes hight, turn the light off, or leave it off.
>
> --
> Chris W
>
> Gift Giving Made Easy
> Get the gifts you want & give the gifts they want
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>
> "They that can give up essential liberty to obtain a little temporary
> safety deserve neither liberty nor safety." -- Benjamin Franklin, 1759
> Historical Review of Pennsylvania

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