@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.