Injector Duty Monitor

[steve ravet]

New pwmeter.zip file uploaded to the ftp site in incoming.

This one has a .gif and .pdf version of the schematic in addition to the
.ps version.  Plus, Georg wrote me a note explaining a little more how
the circuit works, which I've put into the pwmeter.txt file.  I'll also
include his note here:

-------------------------------------------------------
As for the description, it  might be a long one, but i will try and 
keep it short.

If you look at the schematic, you will see that the signal can be 
taken from across the injector or the ecu[switchable]. It is 
optically isolated from the vehicle to eliminate any problems. The 
signal is inverted by the mosfet and the original and inverted signal 
is fed to the interrupt pins of the micro. The reason for this is that 
the int' pins are  neg. edge triggered, and because we want to 
measure pulses widths and period, this is the way it has to be 
configured. 

Now all the micro bit does is when it gets triggered when the 
injector is switched on , a previously configured 16 bit counter 
starts a count with 1us rate. When the injector is shut off, the 
counter stops. This is all done with interrupts, so that all the 
other tasks the micro has to do can carry on without spending time in 
timing loops, ie. handles display routines when not measuring.

Now that the counter has a count eg. 12354 counts x 1us = 12.345ms
This get saved and the counter reset to for the next injector pulse.
The saved value gets displayed on the LCD display in milliseconds. 
Updating of the display is done as and when pulse arrive. If no 
pulses arrive the display will hold the last pulse width.

If you look at the code you will see the bulk of the code is to 
handle the lcd wrt. to formatting the output of it.

Now we could modify the code to measure the period  between injector 
pulses, we could  calculate the duty cycle from that in terms of 
on/off time and percentage. I nfact you could display all of this on 
a 2 line display.That is on-time[ms], off time[ms] and duty cycle[%]. 
If you have eperience with micro's, it should be easy. 
------------------------------------------------------------------

So, this is a circuit that measures the pulse width and displays it on
an LCD screen.  Some small changes would make it calculate duty cycle as
well.

The LCD is part number M1632.  I found 49 of them in stock for $13 ea at
http://www.eio.com/lcd.htm

I've added all this info to a new pwmeter.zip and uploaded it to
ftp://efi332.eng.ohio-state.edu/incoming/pwmeter.zip.  You still need a
device programmer to program the atmel microcontroller though...

--steve