RPM Sensing

[lwindrem]

This works but is much too slow to use with a gas engine 6,100 rpm

Main:
' clear the variables and timer
t1_count = 0
TMR1 = 0 : TMR1 = 0 ' not sure why I have to clear it twice
PIR1.0 = 0


' start the timer and let it count for 1 second
T1CON.0 = 1
PAUSE 1000 ' this has to be shorter than 131072 counts
T1CON.0 = 0 ' Stop the timer
' read the variables and check for an overflow
t1_count = TMR1
IF PIR1.0 = 1 THEN t1_count = t1_count + 65536
' send serial message with count, RPM
HSEROUT ["Count = ", DEC t1_count, " RPM = ", DEC (t1_count * 15 ) , 10,13]
GOTO main

This works but a lot of Jitter

'Each Pulse in Tick = 625nS.
'RPM = 60 / (Ticker * 625nS)
'60 / 625nS = 96000000
'RPM_In = 96000000 / Ticker
Tick = 0 ' Set Var to Zero
D_Tick = 0 ' Set Var to Zero
Ticker = 0 ' Set Var to Zero
Pulsin PortB.0 ,1, Tick ' Measure Pulse Time High Per Rev.
RCTIME PortB.0 ,0, D_Tick ' Measure Pulse Time Low Per Rev.
Ticker = (Tick + D_Tick) ' Ticker = Pulse High + Pulse Low
RPM_IN = (96000000 / Ticker) ' 96,000,000 Devide by Ticker = RPM

HSEROUT " RPM = ", DEC RPM_IN , 10,13]

I know that an interrupt code would be much more accurate and more steady do not know how to start making an interrupt driven code
Help Please

[mpgmike]

TMR1 = 0 : TMR1 = 0 ' not sure why I have to clear it twice

I think you're supposed to:

TMR1H = 0
TMR1L = 0

Your "PAUSE 1000" means that at best, you can only update your t1_count (tachometer) value once every second. Is that sufficient?

I'd like to suggest reading Microchip's AN1980 Application Note. It deals with the Angular Timer function on the PIC16F161x parts, but lots of practical information that should help you.

[lwindrem]

I have Complete Code for a Simple Ignition system 9 pages long -- it works well 100% accurate RPM Readout buut some what over kill for RPM readout
I can display it if someone would be interested helping me trim it.

[richard]

read this
http://www.picbasic.co.uk/forum/showthread.php?t=16153

what you have posted so far is unlikely to get much of a response.
the more info you provide the better, at least post your best attempt {in code tags} with chip type and config, pbp version ...
connection details better still a schematic even hand drawn along with some detail of the tacho input signal and how its been conditioned
to become a useful pic input will help

[Acetronics2]

Have a look here : http://support.melabs.com/forum/picb...-code#post8248

some similarities encountered ...

Alain