Hardware capture on 16F876

[Acetronics2]

Hi, Miniboost

Real world rpm happen in a ... minute !!! ( Mr de la Pallice )

if you want to count in a 1/10 of a second you count ... 15 counts for 9000 rpm ( let's be VERY optimistic !!! ) as tey are INTEGER counts ... you do with 14,15 or 16 .... never 15.238656

Ok ... let's try other methods ...

measure the period ... ahhh, better !!!

with a 4 Mhz clock, using the CAPTURE module of a pic ( 16F628 or 876 i.e ) ... you can have a 1µS resolution ... say 65535 µS period to the max.

Boooo ... can't measure less than 915 rpm !!!

sooo ... let's look at TMR1 prescaler values ... 2 will fit ( 457 rpm ... ok ) also have 4 ...

max rpm resolution ???

9000 rpm is 6.7 ms period ... 3350 TMR1 counts ( W/ prescaler of 2 ) ... say better accuracy than 0.1 %

Now, let's read something clear !!! ... you'll have to use a mean value over a reading period of .5 to 1 sec ... if you do not want the display to flicker too much !!!

but you can also add a fast + mean bargraph ....

Will be another story !!!

Alain

PS: no hardware capture function in PbP ... have to write it yourself ...