Simple pushbutton counter

rickrocker

Hi..

I am trying a very simple experiment: I want to use the pushbutton switches as counters to store a value of the number of times the pushbutton was pressed.

So for example: If I connect a pushbutton switch in the active high state circuit (pressed down denotes a state 1) then it should add a count to a variable, say "result" every time I push the button down. Therefore if I push the pushbutton like 5 times..the variable "result" should display the value of 5 etc etc.

I was playing around with the syntax COUNT [noparse][[/noparse]pin,duration,variable] but I did not get success since the value displayed in the variable is not always the no. of times I pushed the pushbutton ???

I'm suspecting this has something to do with the debounce of the pushbutton or something...could someone clarify!

This is the code I used:

number VAR word

init CON 0

DO

COUNT 0,3000,number

DEBUG CR,CR, "Count is:",DEC number

number = init

LOOP

AND THE RESULTS I'M GETTING ARE RANGING ALL THE WAY FROM 0 - 65535 WHEN I JUST PUSH THE BUTTON LIKE 2 -3 TIMES IN A 3000ms period.

ANY HELP WOULD BE GREATLY APPRECIATED!

thanks

Franklin

You are correct in the fact that your problem is bounce. You could check to see if the button is pressed and then released and then pressed again at a slower rate than count does. like 10 times a second or so.

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- Stephen

erco

Definitely a bounce problem. I'd avoid the count command here. Try something simpler like this and modify as appropriate:


for counter=0 to 255' 255=upper counter limit based on byte variable
DEBUG CR,CR, "Count is:",DEC counter
waithigh:if in0=0 then waithigh' wait until pin 0 goes high via button press
pause 100' wait 100 ms
waitlow:if in0=1 then waitlow' wait until pin 0 goes low via button release
pause 100
next

Those pauses limit how quickly you can press the button, about 5 times per second here with two 100 ms pauses per buttonpress.
For the BS1, change in0 to pin0.

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·"If you build it, they will come."

Tracy Allen

If your pushbutton has a pullup or pulldown resistor, try adding a capacitor in parallel. That can help to surpress the bounce. Suppose the pulldown resistor is 10 kohms. Try a capacitor of 0.1uF. You should also put a resistor of about 200 to 300 ohms out to the switch. The purpose of that is twofold: 1) to protect the stamp against static 2) to protect the switch from excess current.

            10k          220   PB
Vss --o--/\/\--o---/\/\---O^O----Vdd
        |          |
        |          |
        '---||---o----Stamp p0
          0.1 uF

With hardware debounce like that, you can use the COUNT command. It is useful for something like an anemometer or tachometer, where you really need to count pulses for a fixed amount of time. For button presses, there is often some other purpose and you need to do something when the count reaches a set number, rather than counting for a fixed time.

Here is another routine similar to erco's, and this should work even without a capacitor. It double checks the status of the switch:

DO
  DO
    DO:LOOP WHILE in0  ' stays here until pin goes low
  PAUSE 32
  LOOP WHILE in0   ' second check that the pin is really low
  DO
    DO:LOOP UNTIL in0  ' stays here until pin goes high
  PAUSE 30
  LOOP UNTIL in0  ' check it twice
  counter=counter+1
  DEBUG CR,"the count is:",DEC counter
LOOP

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Tracy Allen
www.emesystems.com

jmalaysia

I'm not sure I agree that switch bounce could add up to 65535 in 3 seconds, but I'll leave that one alone!

I don't want to over-complicate the simple experiment, but it is bad practice to use active high switching. Noise very easily causes false switching, especially if you wind up switching inductive loads. With a inactive high state noise only adds to the existing high state, but it's still a high. When your switch is active low you can go to solid ground, which again limits the possibility of noise interference.

rickrocker

Thanks guys for the helpful advice!

rickrocker

10k 220 PB
Vss --o--/\/\--o---/\/\---O^O----Vdd
| |
| |
'---||---o----Stamp p0
0.1 uF

DO
DO
DO:LOOP WHILE in0 ' stays here until pin goes low
PAUSE 32
LOOP WHILE in0 ' second check that the pin is really low
DO
DO:LOOP UNTIL in0 ' stays here until pin goes high
PAUSE 30
LOOP UNTIL in0 ' check it twice
counter=counter+1
DEBUG CR,"the count is:",DEC counter
LOOP

---

Had a question about this code - How do I put this in a subroutine which accepts a user input value of 1 through 6 and then exits the loop. I was thinking if it would be necessary for it to wait for a small period of time to exit the loop with the recorded value (eg: value = 3 and wait for like 1500ms to exit) or should I add a 2nd pushbutton to confirm the value and then exit the loop?

Thanks.