I am tying to interface switched resistors to a micro controller (TI CC3220 - http://www.ti.com/lit/ds/symlink/cc3220.pdf) which uses 3.3VDC for its operation and has an ADC input range of 1.4VDC.
My requirements are
- ADC input should not exceed 1.4 VDC
- The switch has total 6 steps i.e 0 to 5, where in each step different resistor values are used to connect to Vcc and for 0 there wont be any connection to Vcc.
- When the switch resistor module (3 wires to the module) is removed, ADC should always read high.
With my limited knowledge and experience, I have created a schematic as shown below. Would be great if someone can validate it or suggest other solutions to solve my use case.
Note : I do have constraints on additional components and cost, hence a cheaper and optimal solution is preferred. The ADC input impedance as per datasheet is 2.12K
Proposed Schematic (updated on 15-June-2018)