Can someone help simplify the resistor usage in this circuit?
VS is a constant 5v supply. Flex is a variable voltage between 0 and 5v.
The resistors above have been brute forced to achieve this rough voltage range above. Could someone help explain how we could go about simplifying the circuit?
It is essentially a voltage adder and divider which has two possible modes of operation. We can only use resistors as it will be in a very noisy environment and needs to be something an auto electrician can easily add to a vehicle loom.
Mode 1. Low boost with the following voltage mapping.
0v -> 0v
5v -> 700mv
Mode 2. High boost with the following voltage mapping
0v -> 750mv
5v -> 1.25v
edit: Here is the multi sim project if that is of any help https://www.multisim.com/content/ERRVHRCS93ekiEiXBNgbZH/flex-fuel-with-high-and-low-boost-1/open/
edit2: Here is the big picture, maybe someone can help design this better.
We have a single analog input into a vehicle PCM that accepts 0 - 1.66v
We have two inputs we would like to get into the firmware.
Ethanol 0-100% signal which is currently a 0-5v signal.
The state of a switch in the cabin, this is a logical 0 or 1. It is a switch so it can be anything.
We cannot modify the analog input logic as it is in low level firmware, as we are reverse engineering assembler code this would involve modifying the stack which is too complex. We can however use the signals at a higher level within the firmware and use a lookup table to infer the states.
We then have a lookup table that takes the voltage and infers ethanol content.
The lookup table looks like this:
Eg 0 to 0.7v is 0-100% ethanol low boost (eg switch off)
0.75 -> 1.45v is 0-100% ethanol high boost (eg switch on)
Lookup table of volts to % ethanol
Lookup table of high or low boost
What is the best way to multiplex this analog and digital signal into a single analog input?
We have a 5V source available however this needs to be a very simple circuit that can be put within a loom without a PCB at lost cost. Hence the resistor voltage divider/summer we came up with above.