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# LTC2991

Arduino library for an LTC2991 temperature and voltage control IC.


## Description

Experimental - not tested myself, (no hardware)

LTC2991 is an experimental library for the LTC2991 IC which is typically used 
to monitor temperature and voltage. It also has a PWM out to control e.g. a fan.

The IC supports normal voltage measurement (8 lines), differential voltage 
measurements (4 pairs) and temperature measurements (4 pairs). 
These can be combined in a mix. 
As the IC has only 8 inputs available one has to choose what. 

Read the datasheet for the details.


## Interface


### Constructor and setup

- **LTC2991(const uint8_t address, TwoWire \*wire = Wire)**
- **bool begin(const uint8_t sda, const uint8_t scl)** for ESP32 and ESP8266; initializes the class.
sets I2C pins.
returns true if the LTC2991 address is on the I2C bus.
- **bool begin()** UNO ea. initializes the class. 
returns true if the LTC2991 address is on the I2C bus.
- **bool isConnected()** returns true if the LTC2991 address is on the I2C bus.


### Status functions

- **bool new_data(uint8_t channel)** true if there is a new **external** measurement (temperature or voltage) available.
- **bool new_temperature()** true if there is a new **internal** temperature measurement available.
- **bool new_voltage()** true, if there is a new **internal** voltage measurement available.
- **bool is_busy()** true if converting...


### External measurements

The following functions work on pairs

|   n  | selected  |
|:----:|:---------:|
|   1  | V1 V2  T1 |
|   2  | V3 V4  T2 |
|   3  | V5 V6  T3 |
|   4  | V7 V8  T4 |

- **void trigger_conversion(uint8_t n)** wrapper around enable(n, true), better naming.
- **void trigger_conversion_all()** triggers conversions for all 4 channels/pairs.
- **void enable(uint8_t n, bool enable)** enable or disable an external line. 
disable can be used to stop the repeat mode.
- **bool is_enabled(uint8_t n)** idem
- **void enable_filter(uint8_t n, bool enable)** enable filter - not investigated.
- **bool is_enabled_filter(uint8_t n)** idem.
- **void set_Kelvin(uint8_t n)** sets temperature mode to Kelvin, 
implicit set_mode_temperature().
- **void set_Celsius(uint8_t n)** sets temperature mode to Celsius,
implicit set_mode_temperature.
- **void set_temp_scale(uint8_t n, bool Kelvin = true)** used to switch between Kelvin and Celsius.
- **char get_temp_scale(uint8_t n)** returns 'K' or 'C'.
- **void set_mode_temperature(uint8_t n)** sets operational mode.
- **void set_mode_voltage_differential(uint8_t n)** sets operational mode.
- **void set_mode_voltage_normal(uint8_t n)** sets operational mode.
- **uint8_t get_operational_mode(uint8_t n)** returns operational mode.
- **uint8_t get_differential_mode(uint8_t n)** returns differential flag.
- **float get_value(uint8_t channel)** channel = 1..8;
depending on the operational mode it returns the temperature or the
(differential) voltage.


### Internal measurements

- **void enable_Tintern_Vcc(bool enable)** enable internal temperature measurements.
- **bool is_enabled_Tintern_Vcc()** idem.
- **void enable_filter_Tintern(bool enable)** enable filter - not investigated
- **bool is_enabled_filter_Tintern()**
- **void set_Kelvin_Tintern()** use Kelvin.
- **void set_Celsius_Tintern()** use Celsius.
- **void set_temp_scale_Tintern(bool Kelvin = true)** Obsolete?.
- **char get_temp_scale_Tintern()** returns 'K' or 'C'.
- **float get_Tintern()** returns internal temperature.
- **float get_VCC()** returns the internal voltage.


### Configuration

- **void set_acquisition_repeat()** set continuous measurement mode.
- **void set_acquisition_single()** set single shot mode. 
Note that before a measurement one needs to call trigger_conversion();
- **uint8_t get_acquisition_mode()** return mode set (0,1)


### PWM functions

- **void set_PWM(uint16_t value = 0)** value is 0..511
- **void set_PWM(uint16_t value = 0)** value is 0..511, less resolution (256 steps)
- **uint16_t get_PWM()** returns the value from the PWM register, when using PWM_fast this can differ 1.
- **void invert_PWM(bool invert)** idem.
- **bool is_inverted_PWM()** idem.
- **void enable_PWM(bool enable)** idem.
- **bool is_enabled_PWM()** idem.


### Performance

No data available yet.
To be measured when hardware is available...


## Operational

See examples..


### Future

#### must

- get hardware to 
- test test test
- update documentation

#### could

- cache registers (which) or
- cache a number of flags to speed up retrieving data
- optimize multi-byte read / write
- add Fahrenheit 
  - do low level in Kelvin and convert to KFC as needed.
  - would simplify get_value
  - need an enum
- look for code optimizations