How to Calculate time between 2 times press a button

[hoa35ktxd]

My code:

[Mike Walne]

Depends on desired resolution and accuracy.

One way.

1) Create background "tick" using one of the built in timers to drive an ISR.
2) In the ISR increment a counter on each tick
3) Capture the counter value as you press each button.
4) Finish with some maths.
5) Job done.

As your code stands you've got no switch debounce so could have problems.

Mike

[kx9]

My first couple of questions are:
1. How fast do you expect the button presses? Min max
2. What kind of resolution do you need?

[PCM programmer]

These CCS example files may give you some ideas:

[hoa35ktxd]

[hoa35ktxd]

[hoa35ktxd]

[Ttelmah]

I think you need to understand, that this is a help forum for _problems with writing your own code_, not a 'write things for you' forum.
We often do generate code for people, but only once they have started doing it themselves.

Now the CCS examples for things like pulse timing, are as simple as it gets!. The only way to learn, is to start a little at a time. The point is that the PIC has timers, which are just 'counters', which run off a clock you can specify. Once started, they run on their own, whatever your code is doing. So you can time something, by reading the value of one of these, when the first 'event' happens, and then reading it again when the second happens. This is what the pulse example does.

Now step back. the first big problems is the nature of your pulse. If this is a switch signal, then you need to understand the problems of 'bounce'. Except for some very special high speed switches, all switches exhibit 'bounce'. Have a look at:

<http://www.labbookpages.co.uk/electronics/debounce.html>

Do your switches have a debounce circuit?.

Then try something simple. Just have a counter incrementing as your code goes round the loop. Clear this when the first button is seen, and read it when the second occurs. This is going to be a direct measure of the time (in 'loops' rather than mSec). Work out the scale factor from loops to mSec, and you have a working answer. If you want to get a result that won't change as your loop does other things, then try using a timer. The timer will give a figure just like the 'loop counter', but this will be a direct factor of your master oscillator (dependant on the prescaler selected), rather than depending on the code in your loop. MicroChip does a very detailed application note about how the prescalers work, and the timers themselves.

The point is solve one problem at a time.

[Mike Walne]

You've already got a loop.

Follow Ttelmah's advice

Include the following lines in your while(true) loop

[hoa35ktxd]

[hoa35ktxd]

[Ttelmah]

My last paragraph, and Mike's expansion on it, give you a simple place to start.