DIY-WB Display Using KC-5300 - Update

[Peter Gargano]

I finally got around to doing the schematic for the changes needed
to the three digit 7 segment LED Silicon Chip Fuel Mixture Display unit
(also known as the Jaycar KC-5300 kit). The circuit changes are here:

  ftp://ftp.diy-efi.org/incoming/FMD_update.jpg

I'll create some HTML describing the changes to the PCB and the software,
as well as some GIFs of the changes. I'm still tweaking the software to
make it easier to calibrate it using a DVM, battery and small pot.

Briefly, I changed the input circuitry to handle the voltage range of 1.4
to 3.0 Volts, rather than 0.0 to 1.1 for the Bosch LSM-11. This required
a new value for one of the presets (20k -> 5k) and a couple of 5% 1/4W
resistors were changed too.

I'll also provide software that scales to a Lambda rather than an AFR for
those that prefer it. But later too.

The display is most accurate in the rich end of the range and easily gives
0.1 AFR accuracy (which is thus limited by the accuracy of the DIY-WB unit
itself). At the AFR 20:1 range the accuracy is about 0.2 AFR, again limited
by the accuracy of the WB output.

Peter.
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