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Comments regarding increasing number of DS18x20 #561

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Dec 20, 2020
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Comments regarding increasing number of DS18x20 #561

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10 changes: 9 additions & 1 deletion docs/DS18x20.md
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Expand Up @@ -32,7 +32,15 @@ Sensor sends a `tele/%topic%/SENSOR` JSON reponse:
[`TempOffset`](Commands.md#tempoffset) can be used for calibrating the measured temperature. This setting affects **all** temperature sensors on the device.

### Multiple Sensors
Tasmota supports multiple DS18b20 sensors connected to a single ESP8266 chip. At this time, the maximum is set to 8 (see #define DS18X20_MAX_SENSORS 8 in https://github.com/arendst/Tasmota/blob/development/tasmota/xsns_05_ds18x20.ino#L40 )
Tasmota supports multiple DS18x20 sensors connected to a single ESP8266 chip using a single GPIO (multiple DS18x20 GPIO are not supported). The default maximum is set to 8 ([driver code](https://github.com/arendst/Tasmota/blob/development/tasmota/xsns_05_ds18x20.ino#L42)). It is possible to override this number in `user_config_override.h` by adding a line with `#define DS18X20_MAX_SENSORS <new-value>` (ESP8266 only). However one should take into account that:

* Display on the console is limited and SENSOR log will be truncated above 11 DS18x20.
* MQTT buffer length is limited and SENSOR message will be truncated above 18 DS18x20.
* Even less if other sensors are attached to the ESP device and present in the SENSOR message.
* 1-wire has been designed to be a board-bus, not to run through long distances across a whole house. At minimum, use a shielded cable.

!!! note
If you increase the value above default, you are on your own. No support will be provided.

![multiple wiring](https://user-images.githubusercontent.com/5904370/68093672-4b1a2700-fe98-11e9-8c63-3a9b566546b5.png)

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