Push button contact debouncing
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Posted by Allen Bong on July 3, 2007, 7:16 pm
Please log in for more thread options I was constructing a circuit consisting of 20 toggling relays with 20 push buttons on a PCB measuring 7.5 by 8 inches. So I've chosen 4013 as the toggle F/F and the buttons from a VCR front panel was used to send ground to the CLOCK input of the 4013. One of the circuits is as below: (Please view in courier font) |VCC .-. | | 4093 R | | __ '-' +---| \ | | | )o- X +-----------------+----+---|__/ | | o | --- |=| C --- o | | | VCC GND GND | .-. +---+ | | | | \ | |10k GND | +--+----- o o '-' | 4013 | | )| | .--o--. 1k_ |/ V )| | +-----|D S Q|------|___|--| - _)| o | | '--o--' | | pb |=| | | | | o | +--------|--------+ | | | | GND VCC | | + || | 100k VCC +---||--+-|___|--+ || | 100nf | === GND (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de) The relay was chattering seriously and sometimes when the button was pressed, nothing happened. After gathering informations, I came across the circuit using a 4093 schmitt trigger and a pair of RC as a contact debounce, but the R and C was not stated. Can someone tell me what's the best value for a tactile button with the circuit working at 12V ? Thanks you very much. Allen | ||||
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Posted by John Popelish on July 3, 2007, 7:36 pm
Please log in for more thread options Allen Bong wrote: > I was constructing a circuit consisting of 20 toggling relays with 20
> push buttons on a PCB measuring 7.5 by 8 inches. So I've chosen 4013 > as the toggle F/F and the buttons from a VCR front panel was used to > send ground to the CLOCK input of the 4013. One of the circuits is as > below: > (Please view in courier font) > > > |VCC > .-. > | | 4093 > R | | __ > '-' +---| \ > | | | )o- X > +-----------------+----+---|__/ > | | > o | --- > |=| C --- > o | | > | VCC GND > GND | > .-. +---+ > | | | | \ > | |10k GND | +--+----- o o > '-' | 4013 | | )| > | .--o--. 1k_ |/ V )| > | +-----|D S Q|------|___|--| - _)| > | | | | |> +---- > X +-----------|> | | | relay > | | | R Qo-----+ GND | > o | | '--o--' | | > pb |=| | | | | > o | +--------|--------+ | > | | | > GND VCC | | > + || | 100k VCC > +---||--+-|___|--+ > || | > 100nf | > === > GND > > > (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de) > > The relay was chattering seriously and sometimes when the button was > pressed, nothing happened. After gathering informations, I came > across the circuit using a 4093 schmitt trigger and a pair of RC as a > contact debounce, but the R and C was not stated. Can someone tell me > what's the best value for a tactile button with the circuit working at > 12V ? > > Thanks you very much. I would go for a 10 millisecond or so time constant, minimum. That means the product of resistance and capacitance is at least .01, with resistance in ohms and capacitance in farads. One combination would be 10k and 1uF. | ||||
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Posted by Allen Bong on July 3, 2007, 8:50 pm
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> Allen Bong wrote:
> > I was constructing a circuit consisting of 20 toggling relays with 20
> > push buttons on a PCB measuring 7.5 by 8 inches. So I've chosen 4013 > > as the toggle F/F and the buttons from a VCR front panel was used to > > send ground to the CLOCK input of the 4013. One of the circuits is as > > below: > > (Please view in courier font) >
> > |VCC
> > .-. > > | | 4093 > > R | | __ > > '-' +---| \ > > | | | )o- X > > +-----------------+----+---|__/ > > | | > > o | --- > > |=| C --- > > o | | > > | VCC GND > > GND | > > .-. +---+ > > | | | | \ > > | |10k GND | +--+----- o o > > '-' | 4013 | | )| > > | .--o--. 1k_ |/ V )| > > | +-----|D S Q|------|___|--| - _)| > > | | | | |> +---- > > X +-----------|> | | | relay > > | | | R Qo-----+ GND | > > o | | '--o--' | | > > pb |=| | | | | > > o | +--------|--------+ | > > | | | > > GND VCC | | > > + || | 100k VCC > > +---||--+-|___|--+ > > || | > > 100nf | > > === > > GND >
> > (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)
>
> > The relay was chattering seriously and sometimes when the button was
> > pressed, nothing happened. After gathering informations, I came > > across the circuit using a 4093 schmitt trigger and a pair of RC as a > > contact debounce, but the R and C was not stated. Can someone tell me > > what's the best value for a tactile button with the circuit working at > > 12V ? >
> > Thanks you very much.
>
> I would go for a 10 millisecond or so time constant, > minimum. That means the product of resistance and > capacitance is at least .01, with resistance in ohms and > capacitance in farads. > > One combination would be 10k and 1uF.- Hide quoted text - > > - Show quoted text - Thanks John. If I replace the 4093 with a 4069 or 4049, does the circuit still work? The data book says the "rise and fall time" of a 4013 clock input should be 5uS or less. Can the outputs of a 4069 achieve that? Allen | ||||
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Posted by Rich Grise on July 9, 2007, 1:59 pm
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On Tue, 03 Jul 2007 17:50:43 -0700, Allen Bong wrote: >> Allen Bong wrote:
...
>> > send ground to the CLOCK input of the 4013. One of the circuits is
>> > as below: >> > (Please view in courier font) >>
>> > |VCC
>> > .-. >> > | | 4093 >> > R | | __ >> > '-' +---| \ >> > | | | )o- X >> > +-----------------+----+---|__/ >> > | | >> > o | --- >> > |=| C --- >> > o | | >> > | GND >> > GND >> > Thanks you very much.
>>
>> I would go for a 10 millisecond or so time constant, >> minimum. That means the product of resistance and >> capacitance is at least .01, with resistance in ohms and >> capacitance in farads. >> >> One combination would be 10k and 1uF.- Hide quoted text - >
> Thanks John. If I replace the 4093 with a 4069 or 4049, does the > circuit still work? The data book says the "rise and fall time" of a > 4013 clock input should be 5uS or less. Can the outputs of a 4069 > achieve that? > I'd use a 40106 to get six sections - it's got the schmitt trigger input, which is highly recommended for this sort of application, because of the hysteresis. Cheers! Rich | ||||
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Posted by John Popelish on July 9, 2007, 3:37 pm
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Allen Bong wrote: >> Allen Bong wrote:
>>> I was constructing a circuit consisting of 20 toggling relays with 20
>>> push buttons on a PCB measuring 7.5 by 8 inches. So I've chosen 4013 >>> as the toggle F/F and the buttons from a VCR front panel was used to >>> send ground to the CLOCK input of the 4013. One of the circuits is as >>> below: >>> (Please view in courier font) >>> |VCC >>> .-. >>> | | 4093 >>> R | | __ >>> '-' +---| \ >>> | | | )o- X >>> +-----------------+----+---|__/ >>> | | >>> o | --- >>> |=| C --- >>> o | | >>> | VCC GND >>> GND | >>> .-. +---+ >>> | | | | \ >>> | |10k GND | +--+----- o o >>> '-' | 4013 | | )| >>> | .--o--. 1k_ |/ V )| >>> | +-----|D S Q|------|___|--| - _)| >>> | | | | |> +---- >>> X +-----------|> | | | relay >>> | | | R Qo-----+ GND | >>> o | | '--o--' | | >>> pb |=| | | | | >>> o | +--------|--------+ | >>> | | | >>> GND VCC | | >>> + || | 100k VCC >>> +---||--+-|___|--+ >>> || | >>> 100nf | >>> === >>> GND >>> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) >>> The relay was chattering seriously and sometimes when the button was >>> pressed, nothing happened. After gathering informations, I came >>> across the circuit using a 4093 schmitt trigger and a pair of RC as a >>> contact debounce, but the R and C was not stated. Can someone tell me >>> what's the best value for a tactile button with the circuit working at >>> 12V ? >>> Thanks you very much. >> I would go for a 10 millisecond or so time constant,
>> minimum. That means the product of resistance and >> capacitance is at least .01, with resistance in ohms and >> capacitance in farads. >> >> One combination would be 10k and 1uF.- Hide quoted text - >> >> - Show quoted text - >
> Thanks John. If I replace the 4093 with a 4069 or 4049, does the > circuit still work? The data book says the "rise and fall time" of a > 4013 clock input should be 5uS or less. Can the outputs of a 4069 > achieve that? The problem with using either a 4069 or 4049 is that they do not have a snap action (Schmitt trigger), but just amplify the slow rise from the filter capacitor. You can expect a gain of at least 10, probably several times that much, but the rise time of 10 ms at the cap will only be shortened to .1 to 1ms, much slower than the 5us limit. You could cascade several inverters, to speed up that rise, but a Schmitt trigger is definitely the clean way to get a fast rise time out of a slow rise time. An example would be 74HC14. http://w3.id.tue.nl/fileadmin/id/objects/E-Atelier/doc/Datasheets/74hcXX/74hc_hct14.pdf | ||||
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