What is the difference between DS18B20+ and DS18B20+PAR?

The DS18B20+ can be powered from an external power source through the VDD pin, or from the data line using parasite power mode. The DS18B20+PAR can only be powered from the data line using parasite power mode. The DS18B20+PAR does not have a VDD pin. In parasite power mode, an internal capacitor is charged when the 1-Wire signal (connected to the DQ pin) is held high, and is used to power the device. If the 1-Wire signal is held low for a long time, or if 1-Wire signal is heavy loaded, the charge held by the internal capacitor may sufficiently discharge causing the sensor to reset. The transfer distance of a parasite powered device is very low compared to 1-Wire ICs which are externally powered through the VDD pin. For more details please see: GUIDELINES FOR RELIABLE LONG LINE 1- WIRE NETWORKS

How to write and read scratchpad function in arm assembly for the DS18B20?

Please refer to page 18 of Data Sheet as a reference. The commands will be different due to 2 conditions: How many DS18B20s on the BUS; multiple or single? Using parasite power or external? If multiple parts, need master issue reset pulse/DS18B20 response with presence pulse/master issue match ROM/master sends room code/master issue read scratchpad/master read entire scratchpad data. If single part, need master issue reset pulse/DS18B20 response with presence pulse/master issue skip ROM/master issue read scratchpad/master read entire scratchpad data. If parasite power, add DQ line held high by strong pullup before reset.

DS18B20+PAR and cable shielding

Q: How do we shield long probe cables going to DS18B20 to protect from interference due to power cables? Should the shielding be connected to ground at the plug or at the sensor? A: You will want to ground the shield at the socket/plug, not the IC. At the plug, the ground reference should be the same as the PCB/board, and that is the ground we want to reference the shield to.

The DS18B20 outline drawing shows straight pins, but the 3D model shows bent pins, which is correct?

The DS18B20 is sold with straight pins as seen in the package outline. The 3D model shows bent pins so that there is sufficient clearance between the pins for PCB layout, the straight pins of the DS18B20 will need to be bent to suit the PCB layout either by hand or by a lead forming machine.

What is DS18B20+ EEPROM factory default value?

Byte 0 is 50h, Byte 1 is 05h, Byte 2 and Byte 3 is not defined, Byte 4 is 7Fh, Byte 5 is FFh, Byte 6 is not defined , Byte 7 is 10h, Byte 8 is the CRC value of the EEPROM.

What is the current consumption of the DS18B20+?

Current consumption of the DS18B20+ differs based on the type of operation. Standby current can be around 750 to 1000nA at75ºC and can reach 3uA at 125ºC. Standby current can be reduced by ensuring that the DQ signal is in range of GND ≤ DQ ≤ GND + 0.3V or VDD – 0.3V ≤ DQ ≤ VDD. If the sensor is performing operations like temperature conversions or EEPROM writes the current consumption can be around 1~1.5mA.

What is a silicon temperature sensor?

A silicon temperature sensor measures temperature based on the temperature characteristics predicted by the PN junction (transistor emitter junction). These sensors are fabricated by regular semiconductor processes, thus the packaging of various shapes are available, and they come in many different forms, such as: different digital ports and different types of output signals. These are the features which cannot be provided by other technologies. The working temperature range of the temperature sensor IC can be as low as -55°C and as high as +125°C. For some products the upper limit of the temperature can reach around +150°C.

Can the DS18B20 Store Data in the Scratchpad?

The scratchpad of the DS18B20 is intended for configuring the registers of the DS18B20 and should not be used for storage as the data may be lost or corrupted after the device is reset. If indexing of multiple DS18B20 devices is required, each device already has an unalterable unique 1-wire address which can be used to track each device.

In a 1-wire network with multiple DS18B20s, I can read 400 DS18B20 data with expected results when the cable is 30m long. After adding another 200 meters on the bus, the temperature read is much higher than the actual temperature while the ROM ID of DS18B2

It is recommended to measure the resistance of the extension cable. If the cable resistance is too high, the voltage on DS18B20 will drop during temperature conversion. If this is the reason, please 1. Increase the strong pull-up voltage. 2. Replace the cable with a low impedance cable. It is also possible to power the DS18B20 with an external power supply instead of parasitic power.

How can I protect the DS18B20 temperature sensor from moisture?

To ensure the longevity of the sensor in wet environments, a thin layer of conformal coating can be applied to the pins without affecting the thermal response of the device. A conformal coating is a thin, protective coating for PCBs and other electronic components from environments that contain moisture and/or chemical contaminants. Conformal coating can be purchased from a number of electronic retailers, a link to such a retailer can be found below: http://ie.farnell.com/search?st=conformal%20coating

Is it possible to change the internal, factory-set, device address?

Answer: No, it is not possible to change the internal, factory-set device address. DS18B20 does not have a user-configurable address function. Maxim does not offer another, closely similar device which does allow for user configuration of the address.

How many cycles of data acquisition can be made by the DS18B20?

There is no limit to the number of data acquisitions/temperature conversions the DS18B20 can execute. The accuracy of those conversions is guaranteed per the datasheet for the life of the product.

What is the type of temperature sensing element used in the DS18B20?

The DS18B20 uses two matched transistors with known voltage behaviors across temperature. We take the difference of those two voltages and convert that into digital value. See the attached diagram showing the concept.

How can I detect the DS18B20 in a 1-wire network with multiple devices?

The Search ROM [F0h] command will be able to identify the new devices in your network automatically. For example if you had a network of DS2413 devices, and you add a DS18B20 device. After executing the Search ROM command [F0h], you have learned all the address of the devices present on the network, including the new DS18B20 1-wire device. Then, you can send commands to the new device just as you do with your DS2413 devices. Then to address the specific device you send a Match ROM command before sending any commands, as you would when communicating with a single 1-wire device. The basic commands of the DS2413 are the same as the DS18B20, so there should be no issue adding other 1-wire devices to your existing 1-Wire bus. Always check the device data sheets to learn about the differences between devices.

Can the DS18B20 detect air temperature changes?

If the air flows across the DS1820, especially if the DS18B20 is in the TO-92 package which can elevate the package away from the pcb, then the temperature of the air can be sensed.

Do I need to use a pull-up resistor for the DS18B20?

Yes, the DS18B20's DQ pin requires a pull-up resistor to the supply voltage. Even if operated in parasite powered mode (requiring an external MOSFET for the strong pull-up), an external pull-up resistor to the supply voltage is required. The DQ pin is an open drain structure, meaning it has no internal 'high' reference. So an external pull-up resistor is required to provide that high reference.

What causes the SEARCH command to fail at high temperatures?

On some tests, the code works perfectly at room temperature, however when tested above 60°C on a temperature chamber, the 1-wire SEARCH ROM commands fails for some of the devices. One possible cause is that the timing of the 1-wire master can get affected by high heat, so make sure your design is not close to the lower limit of the specified timing requirements. An oscilloscope probe can be implemented to measure the actual tREC at 25°C and again at 60°C to see if there is any observable change in 1-Wire signal behavior. You may want to increase the tREC time (time between read/write time slots). Another possible cause could be leakage currents, which get worse with higher temperatures. It has been seen that active pull-up MOSFET can leak. A solution will be to add a discharge sequence to the code to discharge the gate during start up.

When should the active pull-up be enabled when a DS18B20 is in a one-wire network?

The active MOSFET pull-up should only be enabled after you send a Convert T command to perform a temperature conversion, or after a Write Scratchpad command to write to the EEPROM in the DS18B20. Unless you are performing these two actions, then only a pull-up resistor should be needed on the 1-Wire bus, even in parasite powered mode. If the active MOSFET pull-up is enabled during communication, the DS18B20 1-wire structure will not be able to pull the 1-Wire bus low to respond to any communication. So it is important to only enable the MOSFET for the duration of a temperature conversion or EEPROM write cycle. When not performing either of these two tasks, the MOSFET must be disabled, allowing only a pull-up resistor to act as the high reference for the 1-Wire bus .

How does the DS18B20 measure temperature?

The DS18B20 is a silicon band gap temperature sensor. The sensor is based on the principle that the forward voltage drop of a silicon diode is temperature dependent. By measuring the forward voltage drop across the diode, the temperature of the silicon is calculated.