Turning a light on and off with momentary switch

That's great - thank you sincerely. It appears fairly simple and I look forward to trying to implement it.

This is my first time reading a schematic in ascii, and it mostly makes sense to me. My only question is what does "O" represent? For example, there is an "O" next to CP1. Thanks for your patience.

Regards, Peter

Thanks for the tip. I have used a 555 timer before, but I don't think I ever used it as a one shot circuit, so I'd have to look that up.

Thanks - I think that's exactly the approach that John Fields took in his schematic (see other posting in this thread).

--
The 'O' is used to represent what's called a 'low true' input.  That
is, a desired result occurs as a result of that input being at a
logical '0'.  In this case, that's zero volts or 'ground'  

The other "O"s (at the switch) are just a convention used to denote a
switch (or relay) terminal.

--
Well, in all fairness, Bill's is better than mine in that he has a
single current limiting resistor as opposed to my three.  Since only
one LED will be lit at any given time, there's only a need for one and
it can be connected from the common cathodes of the LEDs to ground.

He's suggested using a 555 to debounce the switch, but my simple RC
may work just as well.  Depends on the switch's bounce
characteristics.

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

Here are my links to electronics distributors (US bias)

I usually use goldmine or futurlec for hobby parts. They don't mind small orders, and don't charge me sales tax (I'm in california)

You can also get samples of parts from distributors like microchip, analog, linear, national, fairchild, etc.

--
Regards,
   Robert Monsen

"Your Highness, I have no need of this hypothesis."
     - Pierre Laplace (1749-1827), to Napoleon,
        on why his works on celestial mechanics make no mention of God.

For another possibility, try this link:

I built a circuit nearly identical to this one, which I control with a small 40MHz radio control. The main problem I have is that the radio control (which I swiped from a toy car) gets occasional hits, which trigger the device without warning. I have it hooked up to a large, lighted, mechanical pink flamingo that my wife decided she needed (and which was on sale for 1/2 price!). Thus, it goes on occasionally by itself, which is actually kinda fun.

The circuit itself is really just an inverter flipflop, like this:

R1 ___ .---------------|___|---------------------------. | | | U1A U1B | | R1 | | |\ ___ |\ | '--------| >O---|___|----------o----| >O----o---' |/ | |/ | \ o | S1 \ | \. | o | | R2 | | ___ | o----|___|---' | --- C1 --- | GND

(created by AACircuit v1.28 beta 10/06/04

except the inverters are NPN common emitter amplifiers instead of inverters. IF you close the switch for a moment, the inverter U1B changes state, thus changing the state of the other inverter. If R2 >> R1, then even when the button is pressed, it won't oscillate. The cap C1 must be large enough to allow the input of U1B to reach it's switching threshold for long enough to switch, despite the action of R1.

--
Regards,
   Robert Monsen

"Your Highness, I have no need of this hypothesis."
     - Pierre Laplace (1749-1827), to Napoleon,
        on why his works on celestial mechanics make no mention of God.

Great explanation! Thank you for providing an architectural synopsis of what's involved. Peter

That's helpful, since I do not yet know the operating characteristics of the LEDs that I will want to use. Thanks, Peter

For me, there is educational value in seeing multiple approaches to the same problem, particularly when someone explains the difference between the various approaches, as you just did. So thank you.

Would you (or any other reader without commercial bias) please recommend an inexpensive and reliable vendor for electronics parts for projects such as this one? If such recommendations are not allowed on the newsgroup, please feel free to email them to me.

Thank you, Peter

an

as

please

Well, you could try Radio Shack, but they seem to have less and less parts available nowadays.

For mail order, I can think of three, but they may require a minimum order.

Also, I have a few items for sale on my website which may be of some use.

The below LED chaser kit for $6.50 would give you most of what you want. A momentary push button, a 10k resistor and a 1uf capacitor in parallel to ground for debounce should be sufficient for manual operation instead of from the 555 timer.

Sadly no. The R/C pink flamingo is destined to remain one of a kind.

--
Regards,
   Robert Monsen

"Your Highness, I have no need of this hypothesis."
     - Pierre Laplace (1749-1827), to Napoleon,
        on why his works on celestial mechanics make no mention of God.

That looks like a handy circuit that could be adapted to my application. I might fiddle around with it and compare to the others. Thanks.

Do they sell any kits for this that include the mechanical pink flamingo? :-)

Peter

flamingo?

I can think of no better way to spend $7,750 ;-) Peter

First question: can I use more than one stage of the LED sequencer to prolong the duration of an LED being on? For example, if I want the first LED to stay on twice as long as the 2nd and 3rd LEDs, is it sufficient to connect the first two outputs to the first LED, and then only one output to each of the other two? In other words, is it a problem to connect two outputs together without using diodes?

Second question: I have decided to use the approach you recommended (using the 4017 with transistors to boost the outputs, as depicted in the link above). In order to drive the process, I would like to use a combination of the simple toggle provided here:

and the 555 for automatic operation. In other words, I would like to be able to switch back and forth between using a momentary switch to control the LEDs and using the 555 to automatically cycle through them. Could someone please explain the circuit design necessary for switching back and forth between the two?

Third question: Alternatively, since the 555 can be used as a debouncer by itself, is it possible to configure the circuit so the 555 could actually be used both as a debouncer for manual operation and as a timer (which would obviate the need for the simple toggle above)?

Fourth question (I think I've well exceeded my quota here): is there any good freeware or open source software for designing circuits and printing out those designs?

Thanks a bunch, Peter

Yes, it is a problem, you need diodes. See my traffic light circuit for an example:

-Bill

Perfect - thank you. Also, that seems like an elegant/parsimonious circuit design.

Incidentally, what software do you use for rendering your circuits designs as they appear on the links you have provided?

Thanks again, Peter