ANOTHER Tachometer Project!!!

[Tom81]

Yep, another tacho project... Just in the process of building a digital tacho - 4 x 7 segment LED display, 16F88 PIC @4MHz.

Hardware is all fine. I can get it to display numbers etc.

Input pulse period is monitored via Timer1 INT on RB0.

BUT, I'm programming in Assembly. So, I need to capture the timer1 value at interrupt, which will give me the period, in µs, in a binary format (Timer1 is a 16-Bit Timer).

My question is: How do I actually convert this into a usable REVS per Minute value?

These are the steps involved, as far as I can work out:

1. determine cycle period (time between each falling edge). This will be a 16-Bit Binary number on Timer1 interrupt.

2. determine Frequency (in revs per minute). This is tricky.

3. convert binary to decimal - can be done, although complicated.

The main problem is dealing with 16-bit numbers with an 8-bit micro.

Anyone know of a SIMPLE way of doing this? any help or ideas would be mcuh appreciated!

Thanks
-Tom

 

[Tom81]

Ok, found a straight-forward method on converting binary to decimal - see Nigel Goodwin's Tutorial website (WinPicProg Page) under tutorial 3 - thanks Nigel!

Still baffled as to how to Convert Period to Frequency (essentially just division)...

 

[Mr RB]

Didn't I send you a Shift-1 Tacho?

That has open source code on the Shift1-LCD page. It's in C but the basic measurement and conversion techniques should be easy to see. I try to use the simplest C coding possible so it can easily be converted to other languages or to assembler etc.

 

[Dragon Tamer]

i know little nothing abou programing, but you've simplified it for me. Thank you So needless to say, but i can't help with your delema too much, but i'll try as best i can. (this is all i can do); if i remember correctly, the frequency is the inverse of the time constant right? if the period and the time constant are the same in this case, just invert your result.

 

[Tom81]

Didn't I send you a Shift-1 Tacho?

That has open source code on the Shift1-LCD page. It's in C but the basic measurement and conversion techniques should be easy to see. I try to use the simplest C coding possible so it can easily be converted to other languages or to assembler etc.

Yeah I saw that. It's easy doing division in C. Not as easy in assembler though! Unless someone has a fast technique?