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 ====== DS18B20 Waterproof Digital Temperature Sensor ====== ====== DS18B20 Waterproof Digital Temperature Sensor ======
  
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 It also features a variety of other possibilities such a powering the device through a pullup resistor connected to the Data line (parasite mode) or setting alarms for a high and a low temperature. It also features a variety of other possibilities such a powering the device through a pullup resistor connected to the Data line (parasite mode) or setting alarms for a high and a low temperature.
  
-{{:amc2020:group_n:ds18b20_img.png?direct| Figure 1}} +^{{:amc2020:group_n:ds18b20_img.png?direct&800| Figure 1}}^ 
-**//Figure 1//** DS18B20 waterproof digital temperature sensor and pins.+|**//Figure 1//** DS18B20 waterproof digital temperature sensor and pins.|
  
 ===== 2. Data Transmission and Working Principle of the Module ===== ===== 2. Data Transmission and Working Principle of the Module =====
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 The 64-bit ROM and the 1-Wire port are connected through the memory control logic to the scratchpad. The scratchpad is a high-speed internal memory that is used for storing small, often temporary, pieces of data which can be rapidly retrieved if needed. The scratchpad memory, which gets erased after powering down, is connected to the temperature sensor itself and stores its data in a 2-byte register. Furthermore, the module has a small EEPROM (Electronically Erasable Programmable Read Only Memory), that means a nonvolatile data storage, which retains the data even when the device is powered down. The Arduino UNO and the ESP32 also have such storages, but of larger size. The module can transfer the aforementioned alarm temperatures TH and TL, as well as the configuration register from the scratchpad into the EEPROM and reload them back to the scratchpad memory after powering up again (figure 2). The 64-bit ROM and the 1-Wire port are connected through the memory control logic to the scratchpad. The scratchpad is a high-speed internal memory that is used for storing small, often temporary, pieces of data which can be rapidly retrieved if needed. The scratchpad memory, which gets erased after powering down, is connected to the temperature sensor itself and stores its data in a 2-byte register. Furthermore, the module has a small EEPROM (Electronically Erasable Programmable Read Only Memory), that means a nonvolatile data storage, which retains the data even when the device is powered down. The Arduino UNO and the ESP32 also have such storages, but of larger size. The module can transfer the aforementioned alarm temperatures TH and TL, as well as the configuration register from the scratchpad into the EEPROM and reload them back to the scratchpad memory after powering up again (figure 2).
  
-{{:amc2020:group_n:ds18b20_block_diagram.png?direct| Figure 2}} +^{{:amc2020:group_n:ds18b20_block_diagram.png?direct| Figure 2}}^ 
-**//Figure 2//** DS18B20 block diagram (Source: {{https://datasheets.maximintegrated.com/en/ds/DS18B20.pdf|DS18B20 datasheet}} p. 5)+|**//Figure 2//** DS18B20 block diagram (Source: {{https://datasheets.maximintegrated.com/en/ds/DS18B20.pdf|DS18B20 datasheet}} p. 5)|
  
 ==== 2.3 Temperature Register ==== ==== 2.3 Temperature Register ====
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 Normally the sensor is in an idle state after powering up. When the MCU issues a Convert T command, the sensor measures the temperature and does an analog to digital conversion and stores the result in the scratchpad 2-byte temperature register (figure 3) and the sensor goes back into idle state. Normally the sensor is in an idle state after powering up. When the MCU issues a Convert T command, the sensor measures the temperature and does an analog to digital conversion and stores the result in the scratchpad 2-byte temperature register (figure 3) and the sensor goes back into idle state.
  
-{{:amc2020:group_n:temperature_register.png?direct| Figure 3}} +^{{:amc2020:group_n:temperature_register.png?direct&800| Figure 3}}^ 
-**//Figure 3//** Structure of the temperature register, LS = Least Significant, MS = Most Significant, S = Sign.+|**//Figure 3//** Structure of the temperature register, LS = Least Significant, MS = Most Significant, S = Sign.|
  
 In the register, the 5 leading bits are representing the sign of the temperature. If the temperature is below 0°C, S = 1 and if it is above 0°C, S = 0. The other 11 bits represent the temperature indicated in figure 3, where bit 0, 1 and 2 can be undefined depending on the resolution stored in the configuration register: In the register, the 5 leading bits are representing the sign of the temperature. If the temperature is below 0°C, S = 1 and if it is above 0°C, S = 0. The other 11 bits represent the temperature indicated in figure 3, where bit 0, 1 and 2 can be undefined depending on the resolution stored in the configuration register:
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 The maximum range of values that can be displayed is thus -127.9375 – 127.9375, which exceeds the range of the temperature sensor. Some examples of different temperatures displayed in 12-bit resolution can be seen in table 1. The maximum range of values that can be displayed is thus -127.9375 – 127.9375, which exceeds the range of the temperature sensor. Some examples of different temperatures displayed in 12-bit resolution can be seen in table 1.
  
-**//Table 1//** Different temperature values and how they are stored in the temperature register.+^**//Table 1//** Different temperature values and how they are stored in the temperature register.^^^
 ^ **MS Byte**  ^ **LS Byte**  ^ **Temperature**  ^ ^ **MS Byte**  ^ **LS Byte**  ^ **Temperature**  ^
 | 0000 0111    | 1101 0000    | + 125 °C         | | 0000 0111    | 1101 0000    | + 125 °C         |
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 The configuration register is stored in the scratchpad memory (and EEPROM) and contains 1 byte of data. The MSB (bit 7) and the 5 LSB (bit 0 – 4) are reserved for internal use and cannot be changed. Bit 6 (R1) and bit 5 (R0) can be changed to adjust the resolution (figure 4). As can be seen, the conversion time doubles each time the resolution is increased by 1. A 12-bit resolution measurement takes 8 times as long as a 9-bit conversion. The configuration register is stored in the scratchpad memory (and EEPROM) and contains 1 byte of data. The MSB (bit 7) and the 5 LSB (bit 0 – 4) are reserved for internal use and cannot be changed. Bit 6 (R1) and bit 5 (R0) can be changed to adjust the resolution (figure 4). As can be seen, the conversion time doubles each time the resolution is increased by 1. A 12-bit resolution measurement takes 8 times as long as a 9-bit conversion.
  
-{{:amc2020:group_n:configuration_register.png?direct| Figure 4}} +^{{:amc2020:group_n:configuration_register.png?direct&800| Figure 4}}^ 
-**//Figure 4//** Schematic of the configuration register and the different thermometer resolution configurations.+|**//Figure 4//** Schematic of the configuration register and the different thermometer resolution configurations.|
  
 ==== 2.5 1-Wire Bus ==== ==== 2.5 1-Wire Bus ====
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 ===== 3. Technical Specifications and Setup of the Sensor ===== ===== 3. Technical Specifications and Setup of the Sensor =====
-When connecting the pins (figure 1), pin 1 (red) is VDD, pin 2 (black) is GND and pin 3 (yellow) is the data pin. In this project two sensors, one measuring the temperature at the bottom of the pond and one at the surface, are connected to the ESP32. As each sensor can be addressed individually by its serial code, the data pins can be connected to the same GPIO pin of the ESP32 (here pin 14 was used). As mentioned before, the sensors need a pullup resistor connecting the data pin with VDD. As both sensors are connected in the same data bus, only a single 5kΩ resistor between their data pins and VDD needs to be added.+When connecting the pins (figure 1), pin 1 (red) is VDD, pin 2 (black) is GND and pin 3 (yellow) is the data pin. In this project two sensors, one measuring the temperature at the bottom of the pond and one at the surface, are connected to the ESP32. As each sensor can be addressed individually by its serial code, the data pins can be connected to the same GPIO pin of the ESP32 (here pin 14 was used). As mentioned before, the sensors need a pullup resistor connecting the data pin with VDD. As both sensors are connected in the same data bus, only a single 5kΩ resistor between their data pins and VDD needs to be added (see figure 5).
  
 Like the DHT-22, VDD can be anywhere between 3.0 V to 5.5 V and can thus be powered by the ESP32 without a problem. Further information on the sensor’s specifications can be found in table 2 and in the datasheet. Like the DHT-22, VDD can be anywhere between 3.0 V to 5.5 V and can thus be powered by the ESP32 without a problem. Further information on the sensor’s specifications can be found in table 2 and in the datasheet.
  
-**//Table 2//** Specifications of the DS18B20 digital temperature sensor (local power supply with ESP32). +^**//Table 2//** Specifications of the DS18B20 digital temperature sensor (local power supply with ESP32).^^^^ 
-^ Sensor                                               ^ DS18B20                                 |||+^ Sensor                                               ^ DS18B20                                 ^^^
 | Supply Voltage $V_{DD}$                              | 3.3 V                                   ||| | Supply Voltage $V_{DD}$                              | 3.3 V                                   |||
 | Pullup Supply Voltage $V_{PU}$                       | 3.3 V                                   ||| | Pullup Supply Voltage $V_{PU}$                       | 3.3 V                                   |||
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 | :::                                                  | 11 bit           | 0.125 °C   | 187.5 ms  | | :::                                                  | 11 bit           | 0.125 °C   | 187.5 ms  |
 | :::                                                  | 12 bit           | 0.0625 °C  | 93.75 ms  | | :::                                                  | 12 bit           | 0.0625 °C  | 93.75 ms  |
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 +^{{:amc2020:group_n:esp32_ds18b20_breadboard.png?direct&650|Figure 5}}^
 +|**//Figure 5//** ESP32 connected to two DS18B20s, here the DS18B20s have 4 pins, white is the data bus, orange is not used.|
 ===== 4. Programming the DS18B20 ===== ===== 4. Programming the DS18B20 =====
  
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   - The variable RESOLUTION stores the resolution of the DS18B20 sensors. As the resolution is not changed during the sketch, it is by default 12 bit.   - The variable RESOLUTION stores the resolution of the DS18B20 sensors. As the resolution is not changed during the sketch, it is by default 12 bit.
   - The variable TCONV stores the time necessary for the sensor to convert the temperature reading to a digital signal and store it in the scratchpad memory with a resolution of 12 bit.    - The variable TCONV stores the time necessary for the sensor to convert the temperature reading to a digital signal and store it in the scratchpad memory with a resolution of 12 bit. 
-  - After issuing a temperature conversion command, the sensor needs a certain time (table 2) depending on the resolution for the data to be actualized. If the temperature data is read before, the old data is retrieved. When powering up the sensor first, the default value for T equals +85 °C. If the delay after the convert command is too short, the readings can be highly erroneous. The necessary time for the conversion is t_delay=t_CONV/2^(12-RESOLUTION) . As it is an integer variable, the conversion time for 10 bit and 9 bit resolution is rounded down. Therefore, a safety margin of 10ms was added here. The function pow() calculates the value of a number that is raised to a power. The first argument is the base, the second is the exponent. Instead, a fixed value for delayTime could have been chosen, but when the resolution would be changed, the fixed value would lead to unnecessary time losses. The expression used here makes the sketch more versatile when the resolution would be changed later on.+  - After issuing a temperature conversion command, the sensor needs a certain time (table 2) depending on the resolution for the data to be actualized. If the temperature data is read before, the old data is retrieved. When powering up the sensor first, the default value for T equals +85 °C. If the delay after the convert command is too short, the readings can be highly erroneous. The necessary time for the conversion is $t_{delay}=\frac{t_{CONV}}{2^{(12-RESOLUTION)}}$ . As it is an integer variable, the conversion time for 10 bit and 9 bit resolution is rounded down. Therefore, a safety margin of 10ms was added here. The function pow() calculates the value of a number that is raised to a power. The first argument is the base, the second is the exponent. It would also be possible to instead chose a fixed value for delayTime, but when the resolution would be changed, the fixed value would lead to unnecessary time losses unless it is adjusted manually. The expression used here makes the sketch more versatile when the resolution would be changed later on by adjusting the delay automatically.
   - The function measureDS18B20Tem() is defined below and performs the temperature measurements and actualizes the variables. It is to be implemented later on in the complete project sketch.   - The function measureDS18B20Tem() is defined below and performs the temperature measurements and actualizes the variables. It is to be implemented later on in the complete project sketch.
   - The actualized string objects containing the temperatures is printed to the serial monitor.   - The actualized string objects containing the temperatures is printed to the serial monitor.
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 </code> </code>
  
-The first sensor (1) was measuring the room temperature on a rather warm day. The second sensor (2) measured the temperature of my hand. Both measurements seem reasonable and when both sensors measure the room temperature, their results are almost equal. However, the temperature probes need some time to get to thermal equilibrium with their environment. When submerged in the water of the pond, this should not be a problem whatsoever.+The first sensor (1) was measuring the room temperature on a rather warm day. The second sensor (2) measured the temperature of my hand. Both measurements seem reasonable and when both sensors measure the room temperature, their results are almost equal. However, the temperature probes need some time to get to thermal equilibrium with their environment. When submerged in the water of the pond continuously, this should not be a problem whatsoever. 
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amc2020/group_n/ds18b20.1594821293.txt.gz · Last modified: 2023/01/05 14:38 (external edit)