circuit help

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psi_wanted
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circuit help

Post by psi_wanted » Wed Mar 27, 2002 10:54 pm

I need a cicuit that has six momentary switches, each hooked to an led. when a switch is pressed the led is activated and stays on. when another switch is pressed it will shut off the previous led and turn on the one connected to that switch. i figured it out using latching relays and a lot of diodes, just looking for an easier way. any takers?? :D

bodgy
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Re: circuit help

Post by bodgy » Wed Mar 27, 2002 11:45 pm

Thyristors (SCR's ) instead of relays could do the trick! Slightly cheaper than relays.<p>bodgy
On a clear disk you can seek forever.

toejam
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Re: circuit help

Post by toejam » Thu Mar 28, 2002 3:47 am

Is this circut follow a sequence?
tj

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Joseph
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Re: circuit help

Post by Joseph » Thu Mar 28, 2002 5:32 pm

I think this idea works as an option: use one cd40106 IC, 3 resistors and two LEDs. Resistors on the LED drives are ommitted because the gate outputs are current limited to about 10mA. I would post it if it were possible. I can email the diagram if you like. Oh, sorry, I see now you want a circuit for 6 switches. I only did it for two.<p>[ March 29, 2002: Message edited by: Joseph Meisenhelder ]</p>

emerson_85
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Re: circuit help

Post by emerson_85 » Sat Mar 30, 2002 8:18 pm

All you need for this circuit is a 74LS373, an inverter (74LS04 or something else that can
invert), 6 diodes, 6 4.7K resistors, and a 220-330 ohm resistor. Oh, and the 6 LEDs and switches, of course.<p>I have posted the schematic at
http://www.apricot.com/~emerson/images/6Buttons.gif<p>where it will remain for at least a couple weeks.<p>Good luck!<p>-Emerson

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Joseph
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Re: circuit help

Post by Joseph » Mon Apr 01, 2002 6:33 am

Emerson, did you forget a pull-down resistor at the input of U2A.

Ron H
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Re: circuit help

Post by Ron H » Mon Apr 01, 2002 10:05 am

This is basically a good idea, but it might not work, due to setup and hold time requirements. The '373 latches on the falling edge of the enable input, and by the time it sees this edge, the input has already gone back high. A '374 should work in place of the '373, but I would add a couple more inverters in series with U2A in order to satisfy the setup time requirement. I still have some concerns about contact bounce causing errors, but it might not be a problem.<p>Ron H

PhilaArt
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Re: circuit help

Post by PhilaArt » Mon Apr 01, 2002 6:21 pm

How about a BASIC stamp and a little software?

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Chris Smith
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Re: circuit help

Post by Chris Smith » Mon Apr 01, 2002 9:00 pm

They make mechanical switches for this. Radios of the older style had five positions, multi line telephones had five positions, and my Video controller has ten positions. They have multiple contacts on each switch for many different things with one of them tapping off to run leds or light bulbs. Check Switch manufactures for one to suit your needs.

psi_wanted
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Re: circuit help

Post by psi_wanted » Tue Apr 02, 2002 7:07 pm

Thanks for all the help everyone. I was thinking of a stamp but thats a little more than I wanted to spend for this. I will probably try the schematic posted.
Thanks Again!! :D

emerson_85
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Re: circuit help

Post by emerson_85 » Sat Apr 06, 2002 12:18 pm

Oops! You're right, I forgot to draw the line
from the last 4.7K pullup resistor to U2A<p>Sorry about that.<p>As for contact bounce, this is not a complex requirement, as originally stated. Even when
the contacts bounce, it won't change the state
of the latched output, unless you're pressing
all the buttons at once or something crazy,
in which case you might get "indeterminate
results." The original poster seemed to be
going for simple and cheap, which is why I posted
what I did.<p>I actually built this before I posted it to
make sure it worked, and it did...mainly because
PCad wouldn't let me simulate the diodes in
the interactive mode (lame!) Guess I have to find
some other software for modelling.

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