Completing the triplet.
R Meter click completes the collection of these really nifty click boards that can be used for quick and dirty measurements while you build prototypes at your workbench.
Like with C Meter click and Am Meter click, there is no single chip that carries the functionality of the entire board. Rather, the design is based on a non-inverting amplifier circuit. The resistor whose value you want to determine is placed in a feedback loop that impacts the amplifier’s gain. This voltage is then fed through a 12-bit ADC before outputting the measurement to the target board MCU through SPI.
The click’s design also implements an elegant solution to enable a very wide measuring range. It has a multiplexer that interfaces directly with the target board MCU. Loaded with the firmware supplied on Libstock, the MCU continually scans the ADC value starting from the smallest resistor range and to determine if its maxed out. If it is, the multiplexer switches its output to calibrate for a stronger resistor. There are four discrete measurement ranges it can cycle through, to give a total range of 0-1 Mega Ohm.