For monitoring or to control a heater/cooler you will need a temperature output. With this module concept it does not matter how the temperature is measured, all that matters is that you have a output instance that uses the reporting format. So you can have thermistors that get masured by an analog pin, whcih you convert with a conversion table to a temperature or you use a chip that you can query the temperature directly.
For all analog inputs that have a nonlinear characteristic, you will need a conversion table that converts a analog signal (value 0..4095) into a temperature in °C. You can define such a table as follows:
#define NUM_MY_TABLE 28
#define MY_TABLE \
{ 4, 864 * 8 }, { 84, 300 * 8 }, { 100, 290 * 8 }, { 116, 280 * 8 }, \
{ 132, 270 * 8 }, { 156, 260 * 8 }, { 184, 250 * 8 }, { 216, 240 * 8 }, \
{ 256, 230 * 8 }, { 300, 220 * 8 }, { 360, 210 * 8 }, { 428, 200 * 8 }, \
{ 512, 190 * 8 }, { 616, 180 * 8 }, { 736, 170 * 8 }, { 884, 160 * 8 }, \
{ 1060, 150 * 8 }, { 1264, 140 * 8 }, { 1500, 130 * 8 }, { 1764, 120 * 8 }, \
{ 2052, 110 * 8 }, { 2352, 100 * 8 }, { 2936, 80 * 8 }, { 3424, 60 * 8 }, \
{ 3752, 40 * 8 }, { 3944, 20 * 8 }, { 4032, 0 * 8 }, { 4095, -20 * 8 }
The table needs a name that is per convention all uppercase. Here it is MY_TABLE. You define a list with {analog value, temperature * 8} seperated by a comma. If you want to split it into several lines finish the last character with a backslash \. All values must be integers so us eonly integer temperatures! The second define is NUM_ plus table name, here NUM_MY_TABLE and contains the number of values.
It is also important that the analog values increase from left to right. This means for NTC sensors the temperatures decrease from left to right while for PTC sensors the temperatures will rise from left to right.
For the typically used case of a 4.7K resistor in series with a thermistor, we have already predefined temperature tables:
| Name | Thermistor |
|---|---|
| Epcos_B57560G0107F000 | Epcos B57560G0107F000 |
| EPCOS_G550 | Epcos G550 |
| ATC_104GT | ATC 104GT |
| Honeywell_135_104LAG_J01 | 100k Honeywell 135-104LAG-J01 |
| Vishay_NTCS0603E3104FXT | 100k 0603 SMD Vishay NTCS0603E3104FXT |
| Sensing_AL03006_58_2K_97_G1 | 100k GE Sensing AL03006-58.2K-97-G1 |
| RS_198_961 | RS 198_961 |
| PT100_5V | PT100 at 5V reference |
| NUM_PT100_3_3V | PT100 at 3.3V reference |
| NTC_3950 | Generic NTC curve with beta 3950 |
| DYZE_DESIGN_500 | DYZE DESIGN 500 |
| B3_innovations_500 | B3 innovations 500 |
| PT1000_4k7 | PT1000 with 4.7k resistor |
| PT1000_1k | PT1000 with 1k resistor |
Depending on the type (NTC/PTC) you can now create a temperature table instance using one of the following methods:
Creates a converter to convert a analog input into a temperature for a table with NTC logic.
IO_TEMP_TABLE_NTC(name, table)| Parameter | Function |
|---|---|
| name | The variable name used to reference this converter later. |
| table | Table name. Do NOT put it in quotes! |
Use the converter as input for temperature reading.
Creates a converter to convert a analog input into a temperature for a table with PTC logic.
IO_TEMP_TABLE_PTC(name, table)| Parameter | Function |
|---|---|
| name | The variable name used to reference this converter later. |
| table | Table name. Do NOT put it in quotes! |
Use the converter as input for temperature reading.
Uses an analog input and a conversion table to gain a temperature. Several instances can share the same conversion table. The variant with _PERMANENT_ERROR will keep an error that happened once until reset to make it easier to find the source.
IO_TEMPERATURE_TABLE(name, analog, table)
IO_TEMPERATURE_TABLE_PERMANENT_ERROR(name, analog, table)| Parameter | Function |
|---|---|
| name | The variable name used to reference this temperature output later. |
| analog | Analog input variable. |
| table | Table converter previously defined. |
Use the output for heater and cooler controls.
Uses an analog input and the equation T = (V - offset) / vPerKelvin to compute the temperature. Several instances can share the same conversion. The variant with _PERMANENT_ERROR will keep an error that happened once until reset to make it easier to find the source.
The AD8495 has 1.25V offset and vPerKelvin 0.005V/K. The AD595 has 0.01V/K.
IO_TEMPERATURE_LINEAR_ANALOG(name, analog, maxVoltage, offset, vPerKelvin)
IO_TEMPERATURE_LINEAR_ANALOG_PERMANENT_ERROR(name, analog, maxVoltage, offset, vPerKelvin)| Parameter | Function |
|---|---|
| name | The variable name used to reference this temperature output later. |
| analog | Analog input variable. |
| maxVoltage | Voltage at maximum analog read. Normally 3.3 or 5.0 |
| offset | Voltage offset for 0°C |
| vPerKelvin | Voltage change per kelvin |
Use the output for heater and cooler controls.
Uses an analog input and Steinhart–Hart equation to gain a temperature. Several instances can share the same conversion table. The variant with _PERMANENT_ERROR will keep an error that happened once until reset to make it easier to find the source. A tool to compute the coefficients from given temperature/resistance values can be found here.
#define IO_TEMPERATURE_BETA(name, analog, beta, seriesResistance, thermistorR25, cCoefficient)
#define IO_TEMPERATURE_BETA_PERMANENT_ERROR(name, analog, beta, seriesResistance, thermistorR25, cCoefficient)| Parameter | Function |
|---|---|
| name | The variable name used to reference this temperature output later. |
| analog | Analog input variable. |
| beta | Beta value from your thermistor. See datasheet. |
| seriesResistance | Resistance of extra resistor on board. Normally 4700 ohm. |
| thermistorR25 | Thermistor resistance at 25°C. Normally 100000 ohm types are used for printers. See datasheet. |
| cCoefficient | C coefficient for Steinhart–Hart equation for thermistor. See datasheet. |
Use the output for heater and cooler controls.
The MAX31855 offers a SPI interface for PT100 sensors. They return the temperatures directly with a resolution of 0.25°C.
IO_TEMPERATURE_MAX31855(name, spiDevice)| Parameter | Function |
|---|---|
| name | The variable name used to reference this temperature output later. |
| spiDevice | Name of the SPI device. SPI mode 0 (software) or 1 (hardware), Max. frequency 5MHz, MSB bit. |
Using software SPI you only need the miso pin for SPI as it is a read only chip.
IO_SPI_SW(SPITc0, 0, 0, true, CS_PIN, CLK_PIN, MISO_PIN, -1)
IO_TEMPERATURE_MAX31855(TempExt1, SPITc0)For hardware SPI you only need to know the chip select pin used.
IO_SPI_HW(SPITc0, 5000000, 1, true, THERMOCOUPLE_0_PIN)
IO_TEMPERATURE_MAX31855(TempExt1, SPITc0)Use the output for heater and cooler controls.
The MAX6675 offers a SPI interface for PT100 sensors. They return the temperatures directly with a resolution of 0.25°C in a range of 0-1023°C. Due to conversion timing required new temperatures are only sampled if at least 230ms are past since last measurement!
IO_TEMPERATURE_MAX6675(name, spiDevice)| Parameter | Function |
|---|---|
| name | The variable name used to reference this temperature output later. |
| spiDevice | Name of the SPI device. SPI mode 0 (software) or 1 (hardware), Max. frequency 4MHz, MSB bit. |
Using software SPI you only need the miso pin for SPI as it is a read only chip.
IO_SPI_SW(SPITc0, 0, 0, true, CS_PIN, CLK_PIN, MISO_PIN, -1)
IO_TEMPERATURE_MAX6675(TempExt1, SPITc0)For hardware SPI you only need to know the chip select pin used.
IO_SPI_HW(SPITc0, 4000000, 1, true, THERMOCOUPLE_0_PIN)
IO_TEMPERATURE_MAX6675(TempExt1, SPITc0)Use the output for heater and cooler controls.
Adds a fake temperature input in case you want to test already without having a working sensor connected.
IO_TEMPERATURE_FAKE(name, fakeTemp)| Parameter | Function |
|---|---|
| name | The variable name used to reference this temperature output later. |
| fakeTemp | The temperature to return on queries. |
Use the output for heater and cooler controls.