Hardware capture on 16F876

hi people ,

if I use
count PORTB.0,100,rpm
the result is poor quality ,

if I use
count PORTB.0,1000,rpm
the result is very slowly ,

if I use hardware capture resolve all that problems ?

how can I use this ?
any body trying ?

regards

COUNT is dependant on the oscillator speed. I don't know what speed you're running, but might help one of those cases if you bumped up the clock speed until you get what you want (maybe)...

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 ...

hello again friends ,
I want make a fast rpm meter ,you understand me ofcourse ,

now I just trying on my car ,its my first dynamic test for this.
Im connect pic`s (portc.2) to car ecu rpm out .
(its same to dash board tacho in )

pic is 16F876-20
osc is 4 mhz ,I can easly rise up but I thing its not enough ..
when I use count 1000 command ,I can read on the lcd "35" every second .

then I change setting ..
35*60/2=1050 rpm ..
its near real rpm ..
I read on the tacho 1000 rpm ..
1000/60 =16.6
16.6*2 =~33.2 I think

So ,count command is very slow .

@skimask ,
Its very easy for me ,
I can try with 20 mhz osc .
Can I try ?

@Acetronics ,
Yes ,
I must write my hardware capture command ,
but question is HOW :)
I understand your comment ,
if I write that codes and If I use 4mhz osc ,
I can easly and faster read on my lcd 1000 to 9000 rpm ?

Tonight Im read 16F876 pdf file and work some new codes .


http://img116.imageshack.us/img116/2946/rpm1tm9.jpg

[QUOTE=MaxiBoost;Yes ,
I must write my hardware capture command ,
but question is HOW :)
I understand your comment ,
if I write that codes and If I use 4mhz osc ,
I can easly and faster read on my lcd 1000 to 9000 rpm ?

[/QUOTE]

How ...

Take 876 Datasheet on $ 8.0, 8.1 ... CCP modules ...

an see which registers you have to deal with ...

For a first trial ... i suggest you to poll the interrupt flag rather than use an interrupt ...

for speed ... Haha ... the time is that of 1 rotation or time between two sparks ( half a rotation ...if i'm right !!! )

Alain

Quote:

---

Originally Posted by Acetronics

the time is that of 1 rotation or time between two sparks
Alain

---

What if I've got a diesel?

Hi Skimask

You get the right to come back for 2nd week challenge !!! ...

1 rotation ... fits Diesel ALSO !!!

Ok ... can try to get the 3 phases from alternator ... but I read somewhere in this thread : ECU rpm output ...

France : 2 more points !!!

LOL !!!