LapX9C10X

An Arduino library to drive the X9C102, X9C103, X9C104, and X9C503 Digitally Controlled Potentiometers. The four members of the family have these resistances:

 X9C102 = 1k
 X9C103 = 10k
 X9C503 = 50k
 X9C104 = 100k

These chips are controlled by a three wire interface, consisting of:

Up/Down (U/D)

The U/D input controls the direction of the wiper movement and whether the counter is incremented or decremented.

Increment (INC)

The INC input is negative-edge triggered. Toggling INC will move the wiper and either increment or decrement the counter in the direction indicated by the logic level on the U/D input.

Chip Select (CS)

The device is selected when the CS input is low. The current counter value is stored in non-volatile memory when CS is returned high while the INC input is also high.

The library

The library allows you to set resistance values either by using the counter values used internally by the chips (0 to 99), or by specifying the resistance value you want directly in kilohms. (All resistances refer to the resistance between the low end of the potentiometer - the VH/RH pin, and the wiper - the VW/RW pin.)

When this document refers to forcing the wiper to a position, this means that it will not assume anything about where the wiper currently is, but will 'force' it. This entails either moving the wiper 99 steps up (ensuring that it is set to 99), or moving it 99 steps down (ensuring that it is set to 0). This is necessary because there is no way of reading the wiper postiton from the chip.

LapX9C10X is invoked as:

LapX9C10X(uint8_t incrementPin, uint8_t upDownPin, uint8_t selectPin, float resistance);

Where the resistance parameter can be one of:

LAPX9C10X_X9C102       (1 kOhm)
LAPX9C10X_X9C103       (10 kOhm)
LAPX9C10X_X9C503       (50 kOhm)
LAPX9C10X_X9C104       (100 kOhm)

or can be the actual resistance of the potentiometer (in kilohms), as measured between VH/RH and VL/RL (when the chip is powered on). Using the actual resistance will of course give more accurate results, as the tolerance of the parts is ±20%.

The chips contain non-volatile memory, and can be programmed to power up to any of the 100 available wiper positions. LapX9C10X has a function to save to this memory.

When using LapX9C10X functions that are passed a 0-99 wiper position, or a 0-max resistance, any value that is less than zero is changed to zero, and any value that is higher than the maximum is changed to the maximum.

The functions provided by LapX9C10X are:

void begin();

void begin(int);

This must be called before using any other function. If called with no argument, it forces the wiper to 99 – the maximum. If called with any negative value, it forces the wiper to 0 – the minimum. Any value from 0-99 tells LapX9C10X to assume the power up value to be that number, and it will not change it. Use this with care, as if you give it an incorrect value, all operations you then perform will also be incorrect.

void set(int wiper);

void set(float resistance);

If passed an integer, sets the wiper to that value (0-99). If passed a float, sets the wiper to the position that is closest to the resistance given (in kilohms).

void offset(int change);

Moves the wiper change amount – that is, it adds or subtracts change from the wiper position.

void reset(int wiper);

Forces the wiper to the value given, ignoring LapX9C10Xs idea of where the wiper currently is. It does this by first forcing the wiper to the end nearest the desired position, then moving it from there.

uint8_t get();

Returns the current wiper position.

float getK();

Returns the resistance of the current wiper position (in kilohms).

void writeNVM();

Writes the current wiper position to the chip’s non-volatile memory.