Re: Turning a light on and off with momentary switch

From: petrus bitbyter (p.kralt_at_reducespamforchello.nl)
Date: 02/17/05 

Date: Thu, 17 Feb 2005 15:34:54 GMT

"Chris W" <1qazse4@cox.net> schreef in bericht
news:vJWQd.64020$jn.59932@lakeread06...
> petrus bitbyter wrote:
>
>>
>> Chris,
>>
>> What kind of lights do you want to switch? It makes a lot of difference
>> whether you want to switch a LED (~40mW) or a 100W incandescent bulb.
>>
> For the first application I just want to switch 1 or maybe 2 LED's hooked
> in parallel. They could be of different colors and therefore different
> voltages so I am guessing even for just one led on each line I probably
> need some kind of a driver so I can match the voltage and current for each
> load. Future applications will need to switch around 10W lights, probably
> in the form of groups of LEDs, on and off.
>

One or two LEDs in series can be driven by some logic devices. For more LEDs
or lamps you will need a transistor driver or a relay.

>
>> LEDs can be controlled easily using electronics and that's where the
>> flip-flop appears. You need a so called T-flipflop but they are not very
>> common. Use an D-type flipflop instead and connect the inverted Q-output
>> (/Q) to the D-input. Every pulse on the clock input will make the
>> flipflop change state. So a pushbutton on that input will theoretically
>> do the job. But a flipflop is a high speed switching device and will see
>> a lot of pulses every time you push and you can not predict the last one.
>> So you need to debounce your pushbutton carefully which requires some
>> extra electronics.
>
> After some more reading on flip flops I figured this out on my own. If
> you read my post in 2-14-2005, you can read more about my application.
> What I would really like to find is an IC with as many as 16 D flip flops
> that are already wired up like you described. I don't suppose finding
> that is likely?
>

Missed your post of 2-14-2005. Can't even find it in the Google groups.

AFAIK such a device does not exist and its very unlikely you'll ever find
one. You can design one for yourself using PLDs but that requires quite some
skills and programming equipment. Especially if you want to incorporate
debouncing. Even then you wil need power drivers to control loads over some
hundreds of mW.

>>
>> Of course you can use a microcontoller as wel. Microchip sells 6 pins
>> ones these days and the only extra components you need is the pushbutton,
>> the LED and maybe two resistors. The problem of course is skills and
>> equipment to program them.
>
> I'm thinking about getting one of the RABBIT modules, that way I don't
> think I need a separate programmer do I?
>

FAIK RABBIT devices also requires programming which can be done using C. You
will also need a pretty expensive development system and the modules
themselves does look like to be cheap either.

Did you realise a module like you want, needs at least 34 pins? I think a 40
pins micro comes most close to that. A PIC16F877 is one of the cheaper
<$10,-- examples. Software is free from Microchip and programming tools can
be bought or home made. You can find a lot of information on
http://www.voti.nl/swp/n_index.html
but it's for sure not the only one a the on the net.

> --
> 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

petrus bitbyter

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