mirror of
https://github.com/RobTillaart/Arduino.git
synced 2024-10-03 18:09:02 -04:00
172 lines
5.8 KiB
Markdown
172 lines
5.8 KiB
Markdown
|
|
[](https://github.com/marketplace/actions/arduino_ci)
|
|
[](https://github.com/RobTillaart/MAX14661/actions/workflows/arduino-lint.yml)
|
|
[](https://github.com/RobTillaart/MAX14661/actions/workflows/jsoncheck.yml)
|
|
[](https://github.com/RobTillaart/MAX31850/blob/master/LICENSE)
|
|
[](https://github.com/RobTillaart/MAX31850/releases)
|
|
|
|
|
|
# MAX31850
|
|
|
|
Arduino library for the MAX31850 / MAX31851 thermocouple sensor.
|
|
|
|
|
|
## Description
|
|
|
|
**WARNING EXPERIMENTAL** needs more testing (no hardware yet).
|
|
(feedback welcome)
|
|
|
|
his MAX31850 library is not a full featured library for the MAX31850 family.
|
|
|
|
The MAX31850/1 is a Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converter.
|
|
|
|
The MAX31850/1 supports K-, J-, N-, T-, S-, R-, and E-type thermocouples. (to be tested).
|
|
|
|
The library supports both the MAX31850 and MAX31851 but is limited to one sensor per pin.
|
|
The only feature the class supports is the asynchronous reading of the temperature.
|
|
|
|
This allowed the class to be both minimal in size and non-blocking.
|
|
In fact the class has no support for a synchronous read in one call.
|
|
This choice will teach people how to work in a non-blocking way from the start.
|
|
|
|
Finally this library will probably make it easier to use a MAX31850 with processing
|
|
boards or IC's with small memory footprint.
|
|
|
|
The MAX31851 is (for now) functional identical to MAX31850.
|
|
|
|
|
|
## Hardware connection
|
|
|
|
```
|
|
// PROCESSOR MAX31850 THERMOCOUPLE
|
|
// +---------------+
|
|
// GND 1 | o o | T+
|
|
// DATA 2 | o |
|
|
// VCC 3 | o o | T-
|
|
// | |
|
|
// | oooo |
|
|
// +---------------+
|
|
// 4 address pins.
|
|
```
|
|
|
|
This library supports only one MAX31850 per Arduino/ MCU IO pin.
|
|
|
|
|
|
#### Pull up resistor
|
|
|
|
Connect a pull-up resistor 4.7 KOhm between DATA (pin 3) and VCC (pin 2).
|
|
When the wires are longer this resistor needs to be smaller.
|
|
|
|
An **indicative** table for pull up resistors, (E12 series), to get started.
|
|
|
|
Note: thicker wires require smaller resistors (typically 1 step in E12 series)
|
|
|
|
| Length | 5.0 Volt | 3.3 Volt |
|
|
|----------------:|-----------:|-----------:|
|
|
| 10cm (4") | 10K0 | 6K8 |
|
|
| 20cm (8") | 8K2 | 4K7 |
|
|
| 50cm (20") | 4K7 | 3K3 |
|
|
| 100cm (3'4") | 3K3 | 2K2 |
|
|
| 200cm (6'8") | 2K2 | 1K0 |
|
|
| 500cm (16'8") | 1K0 | \* |
|
|
| longer | \* | \* |
|
|
|
|
\* = no info, smaller
|
|
|
|
|
|
## Interface
|
|
|
|
```cpp
|
|
#include "MAX31850.h"
|
|
```
|
|
|
|
|
|
#### Constructor
|
|
|
|
- **explicit MAX31850(OneWire \* oneWire)** constructor.
|
|
- **bool begin(uint8_t retries = 3)** initialize the library.
|
|
Returns true if addresses are found.
|
|
Nr of retries can be adjusted if needed, default 3.
|
|
- **bool getAddress(uint8_t \* buffer)** get the address if found.
|
|
|
|
|
|
#### Read the sensor
|
|
|
|
- **void requestTemperatures(void)** Asynchronous request to start conversion.
|
|
- **bool isConversionComplete(void)** CHeck if requested conversion is done.
|
|
- **float read(void)** read the data from the sensor.
|
|
Returns the temperature of the thermoCouple as this is most often needed.
|
|
- **float getTempTC(void)** returns temperature of the ThermoCouple from cache.
|
|
One must call **read()** again to get new measurements.
|
|
- **float getTempInternal(void)** returns internal temperature from cache.
|
|
One must call **read()** again to get new measurements.
|
|
|
|
|
|
#### Other
|
|
|
|
- **uint8_t getAddressPins()** binary form of the 4 address bits. 0x00..0x0F.
|
|
- **uint8_t getErrorCode()** get the internal error code. See below.
|
|
- **bool setTypeTC(char typeTC)** typeTC is one char from E J K N R S T
|
|
- **uint8_t getTypeTC()** returns the current TC type.
|
|
|
|
|
|
## Types of thermocouples
|
|
|
|
The MAX31850 comes in MAX31850E.. MAX31850T types reflecting the version of TC to use.
|
|
|
|
|
|
| Sensor type | SC in µV/°C | Temp Range in °C | Material | notes |
|
|
|:-------------:|:--------------|:-------------------|:----------------------------|:------------|
|
|
| E_TC | 76.373 | -270 to +1000 | Constantan Chromel |
|
|
| J_TC | 57.953 | -210 to +1200 | Constantan Iron |
|
|
| K_TC | 41.276 | -270 to +1372 | Alumel Chromel | most used |
|
|
| N_TC | 36.256 | -270 to +1300 | Nisil Nicrosil |
|
|
| R_TC | 10.506 | -50 to +1768 | Platinum Platinum/Rhodium |
|
|
| S_TC | 9.587 | +50 to +1768 | Platinum Platinum/Rhodium |
|
|
| T_TC | 52.18 | -270 to +400 | Constantan Copper |
|
|
|
|
(MAX31851 idem)
|
|
|
|
|
|
## Error codes
|
|
|
|
| name | value |
|
|
|:--------------------------|:-------:|
|
|
| MAX31850_OK | 0 |
|
|
| MAX31850_ERR_SHORT_OPEN | 1 |
|
|
| MAX31850_ERR_SHORT_GND | 2 |
|
|
| MAX31850_ERR_SHORT_VDD | 4 |
|
|
|
|
|
|
## Future
|
|
|
|
#### Must
|
|
|
|
- improve documentation
|
|
- get hardware to test (sponsors welcome)
|
|
- test on different platforms
|
|
|
|
|
|
#### Should
|
|
|
|
- investigate different thermocouples
|
|
- test with different platforms
|
|
- has the 31851 special features to implement?
|
|
|
|
|
|
#### could
|
|
|
|
- extend error handling
|
|
- expand to multi sensor per pin.
|
|
- first get one sensor working
|
|
- investigate range checking on type TC
|
|
- need setType() and more.
|
|
- need lower upper range = int16_t will do.
|
|
- add CRC check
|
|
- + error code
|
|
|
|
|
|
#### Wont
|
|
|
|
|