@redplc/node-red-rpi-ds18b20

Node-RED node for ds18b20 temperature sensor using with redPlc nodes

ds18b20 digital temperature sensor

• 9..12bit resolution.
• Conversion time 93.75..750ms.
• Measure range -55°C .. +125°C.
• On range -10°C .. +85°C is accuracy ±0,5°C.
• 1-Wire connection.
• Power supply 3..5.5V external or over bus (parasite power).
• Each sensor has a 64-Bit ID.

Usage

• Install redPlc nodes.
• Use redPlc s-inject node for trigger update.
• Connect to first output on s-inject node.
• For logical operations use redPlc nodes.
• Data is exchanged with global context variable arrays.
• Array index depends on the order of the sensors.
• If you add/remove sensors, array index can be change.
• This node works on Raspberry Pi with 32bit or 64bit OS.
• The temperature values are in °C or °F.
• To prevents locks only one node is allowed.
• Enable 1-wire with raspi-config.
• Default 1-wire pin on Raspberry pi is GPIO4.

Delay with reading multiple ds18b20 digital temperature sensor

The ds18b20 digital temperature sensor needs to read temperature:
9-bit resolution -> 93.75ms.
10-bit resolution -> 187.5ms.
11-bit resolution -> 375ms.
12-bit resolution -> 750ms. (default factory set)
Because the accuracy is ±0.5°C in the range from -10°C to +85°C,
I recommend operating the sensor with 9-bit resolution.
Please note that the times apply to one sensor.
This means 10x750ms (7.5s) for 10 sensors with 12bit resolution.
There is a way to read multiple sensors more quickly.
The 1-Wire drivers from RPi Linux are not used for this,
but the sensors are addressed with their 1-Wire protocol.
In the further version I will implement this 1-Wire protocol.

Set Sensor Resolution

You can change the sensor resolution with tool in subfolder setSensor.
File readme.txt describes how the tool is used.