The MAX681* series of switch debouncers look useful but they're quite pricey at >$1 for the single MAX6816 and several $$ for the octal 6818. Are there any cheaper, easily available alternatives?
For those who are not familiar with the series, these are externally simple devices that have pins for each mechanical switch and for the debounced output. Nothing else apart from Vcc and ground. The 40ms debouncing is done internally without any external component.
Hex schmitt-triggers? Most versatile solution would be a small uc.
-- Dipl.-Inform(FH) Peter Heitzer, peter.heitzer@rz.uni-regensburg.de
I used a maxim reset chip.... if you can live with the 140mS odd delay.. No doubt Microchip do something similar....
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It pains me to note...
How about a magnetic switch, with the hysteresis in the Hall chip? TCS40nnn goes for under $0.20 in hundreds. It used to be common to get these in pushbutton form for keypads, but there's a dearth of supply of those nowadays (I've got a bottle of the suckers somewhere...).
Change the switch to SPDT, earth the centre and use 2 pullups with cross coupled nands as a set reset FF. Instant action, no bounce.
I've used both approches but they require external components and/or programming. The MAX chips need neither.
Examples?
There's the hoary old MC14490 hex contact bounce eliminator for about the same money ($3.50 in reels). Alternatively, use an SPDT and an RS flipflop, or a 10-ms RC and a Schmitt trigger.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
On a sunny day (Wed, 12 Aug 2020 10:27:31 +0100) it happened Tom Gardner wrote in :
An SPDT switch is less common than an SPST one and the circuit needs the pull-up resistors. Besides, if the switch has to be at some distance from the FF, it needs two lines to connect the two.
There are various ways to achieve bounceless switching and I've used them before. What makes the MAX681x attractive is that it can use common SPST switches and doesn't need any external
Please see my replies to Don Y and to Andy Bennet.
Interesting. I don't remember using any Padauk product but I've used some by Holtek.
The cheapest MCU with internal clock you can find?
Best regards, Piotr
Or simpler, less wiring, less ICs:
- Connect both ends of all SPDTs to GND and VCC
- Wire the contact to a non-inverting buffer input, with 330 Ohms between output and input. Only one signal wire per switch needed, and instant action.
/------ 330R ---\ VCC ----o\ | |\ | \----+-----| >-------+--- out GND ----o |/
Regards, Arie
Any of the 3 pin uP reset chips will work. You can get them for $0.25 and less. You do have to have an external pulldown from chip vcc to ground. Pushbutton interrupts vcc to the chip. Reset output will go low V and then high after some time period, some chips are 200ms, some 140, check the data sheets.
-- Chisolm Texas-American
The MAX809 series has all sorts of uses. The best part is that you don't have to buy them from Maxim.
But as a debouncer, you'd need more parts. Some other POR chips might not.
A Schmitt gate would need an RC per switch, which could be in quad packs.
Why do you need to debounce?
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Some flops can be forced at their outputs, so just ground Q or Qbar with an SPDT switch.
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Thanks for the 809. I've used TI and ST parts as debounce but both needed a pull down from vcc to be reliable.
-- Chisolm Texas-American
If it's got an 8 bit ADC you can debounce 5 or 6 button per port with some averaging and a state machine.
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