I can understand why if you did it for a living, it might lose its charm factor.  But, being an amateur - its a fascinating field that enables you to design and make all sorts of fascinating devices - fairly cheaply - compared to trying to do the same with an Analog design approach. 

 

My old analog EFI Fuel monitor I designed and built several years ago worked just fine, but it could only provide fuel flow and fuel total.  Furthermore it had over 7 major chips (counters, gates, inverters) not to mention the resistors and capacitors.  It had a larger foot print appro 3 x 6" and the components total cost was much more than a microchip and its relative few supporting components. I tried 3 different redesigns to give it more capability and finally decided it was just too limiting for the amount of effort - so decided to jump into the digital world.

 

 But, I will admit at times wrestling with the code, I was not certain I had made the right choice to go digital.  Fortunately after slowly getting started with the assembly language coding, I found a Pascal Compiler designed for the Microchip PIC chips - Heaven sent - I could code in English (more or less), plus it a library of many of the basic I/O functions I needed.  However, it did not have floating point nor even integer math operations larger than a word (2 byte) size. I was dealing with numbers as large as 60,000,000 (clock counts).   So I had to write most of the math routines I needed in assembly including such basic things as putting a decimal in a number at the right location.

 

But, it was truly education (and I must admit very fun and satisfying when it finally worked like I had designed it t).  Going out this morning with that offending line of code removed and the two modules I have built test and retest.

 

The only difference in the two modules  is one has an LM9040 Lambda (O2) amplifier and the other one just reads the voltage from the 02 sensor directly - wanted to see if the LM9040 did anything for the Air Fuel Indication - basically all it does is expand (amplify) the 0 -1volt O2 sensor output to 0 -5 volts for the CMOS chip. I thought that might provide more "sensitivity" through the chips A/D circuit - but as Tracy commented why worry about sensitivity when we are just using it for a "relative indication:.

 

Actually, I have coded a screen that shows the O2 sensor output in volts (millivolts), but decided that a visual indication of lean rich didn't require any mental manipulation of the voltage to A/F, so went with a visual indication on the LCD display.

 

Onward!

 

Ed