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Old 17th July 2003, 12:08 AM   #1
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Default ever make a switch?

i need a heavy duty (for footswitch) SPDT momentary switch. i need it to toggle a D flip-flop and i can't figure out how to debounce a clock without two throws.

i figure i can get some pieces of metal and something bouncy/spongy ...

any suggestions?

know of another way to use digital stuff to toggle a relay on and off with one switch? i like the D flipflops because i can use one switch to go to all the different preset inputs to turn everything (two or three channels) on at the same time.

is it a bad idea to power a line-level opamp with the same battery (2x9V, probably) that powers the relay coils?
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Old 17th July 2003, 06:46 AM   #2
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Sounds pretty similar to a problem a lot of people have with guitar electonics. The footswitches are all made for switching 120v ac, which can burn through a little crap between the contacts, much unlike the 100 mv guitar signal. So, many times they stop working fairly quickly. To get around this, I use a switch actuator, heres a pic at http://www.smallbearelec.com/Ordering/actuator.jpg . You can buy them at www.smallbearelec.com, and you can put a pcb on standoffs with a momentary switch found at mouser and many other places for 40 cents, and they are good for at least 100k operations. From the momentary switch, its quite simple to make a circuit for whatever you want with logic chips and relays. One similar to the one i use is found at www.geofex.com/FX_images/ltchrly.gif , and its excellent for use with batteries due to the latching relay. I can put my full body weight on the switch and nothing happens due to the shoulder on the actuator. Good luck.

-Chris
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Old 22nd July 2003, 04:51 AM   #3
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Default ever make a switch?

Hi

There is an IC specifically designed for switch debouncing and needs one capacitor to be connected externally.
It is an Hex Contact Bounce Eliminator from Motorola.
The number is MC 14490

Enjoy
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Old 23rd July 2003, 09:34 PM   #4
dhaen is offline dhaen  Europe
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Default Toggle circuit with built in debounce

Hi,

I've used this circuit for years. It works.


Cheers,
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File Type: gif toggle.gif (7.6 KB, 264 views)
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Old 24th July 2003, 08:42 AM   #5
dhaen is offline dhaen  Europe
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Hi,

It has been politely pointed out to me by a fellow member, that this circuit does break one of the design rules:

Quote:
Generally but not compulsarily, unless specified, the inputs of a digital IC are not connected to timing components (RC). This leads to slow rising/falling waveforms which leads to false triggering. These slow waveforms are handled using schmitt input devices (normally gates are available).
This is true.
When such design rules are broken, one consequence can be that a circuit fails to work under certain circumstances eg temperature, different chip make, different switch type etc.

I did not design this circuit myself, but obtained it so long ago that I cannot remember it's source. I've used it 100's of times, and it has not failed (yet) for me, though by the "rules" one day it will.

If 100% reliability is required, a dedictated de-bounce chip would be desirable.

Thanks for the advice.

Cheers,
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Old 24th July 2003, 09:04 AM   #6
StuartH is offline StuartH  South Africa
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Hi

I have had similar problems in the past, but while reading the thread, had a thought.

Could one not use a magnetic reed relay? Either as the switch itself, or to trigger an instrumentation grade relay.

The spacing between the reed and magnet would be important, however it would last for ages, and no mechanical parts!

Cheers,
Stuart
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Old 25th July 2003, 02:32 AM   #7
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i think i will try that circuit. allelectronics has some pretty tough looking SPDT momentary switches.

neither digikey nor mouser have MC 14490s,
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Old 25th July 2003, 03:08 AM   #8
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looks good?
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File Type: jpg bounce.jpg (4.9 KB, 182 views)
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Old 25th July 2003, 09:34 AM   #9
dhaen is offline dhaen  Europe
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Quote:
Originally posted by travis
looks good?
Better but I don't know if it will be tolerated in the feedback from -Q to D.
It'll take no time to try though.

Cheers,
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