Hardware capture on 16F876

[MaxiBoost]

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

[skimask]

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)...

[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 ...

[MaxiBoost]

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

[Acetronics2]

[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

[skimask]

the time is that of 1 rotation or time between two sparks
Alain
What if I've got a diesel?

[Acetronics2]

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 !!!