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https://github.com/eigenein/ntc-one-wire

NTC thermistor to 1-Wire converter on Arduino Nano
https://github.com/eigenein/ntc-one-wire

1-wire adc-device arduino arduino-nano arduino-sketch atmega328p dallas dallas-temperature diy ds18b20 livolo livolo-thermostat measurements ntc ntc-thermistor onewire-slaves sensor temperature thermistor thermometer

Last synced: 21 days ago
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NTC thermistor to 1-Wire converter on Arduino Nano

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README 

        
I've made this device to connect my [NTC thermistor](https://en.wikipedia.org/wiki/Thermistor#NTC) to a [Livolo thermostat](https://www.livolo.eu/c-4632899/livolo-thermostat/) which only works with a built-in [DS18B20 digital thermometer](https://www.maximintegrated.com/en/products/sensors/DS18B20.html).



[![Latest GitHub tag](https://img.shields.io/github/v/tag/eigenein/ntc-one-wire?logo=github)](https://github.com/eigenein/ntc-one-wire/releases)

[![Built with Arduino Nano](https://img.shields.io/badge/Arduino-Nano-green?logo=arduino)](https://www.arduino.cc/en/Guide/ArduinoNano)

[![Built with PlatformIO](https://img.shields.io/badge/Built%20with%20♥-PlatformIO-blue)](https://platformio.org/)



## Instructions



### [`table.h`](src/table.h)



You need to generate the [`table.h`](src/table.h) for your particular NTC thermistor. It contains an array which maps a measured ADC value to actual temperature. You can do this via the provided [`table.py`](table.py) script.



Measure your NTC resistance at two different temperature points. Then call [`table.py`](table.py) specifying your measurements:



```sh

python table.py \

    --t1  --r1  \

    --t2  --r2  \

    --rf 

```



If your program memory is too small, you can specify `--min-t` and/or `--max-t` parameters. Then the table will be generated in a specified temperature range generating less array entries thus taking less memory.



See [Measuring the temperature with NTCs](http://www.giangrandi.ch/electronics/ntc/ntc.shtml) for more information on how the conversion is implemented.



### Schematic



- `R2` is a fixed resistor with a known resistance. Start with a one that is close to your typical NTC resistance. I recommend to measure actual resistance of the resistor before passing it as `--rf` to improve readings accuracy.

- `C1` aims to filter noise on the NTC wires. It may be tempting to remove it but then you'll sometimes get inadequate readings. You may adjust it though depending on how fast temperature changes in your setup.

- I use `MISO` pin for 1-Wire data line because then I'm able to solder the power and data wires close to each other [on the ICSP header](https://www.arduino.cc/en/reference/SPI).

- I used a self-fusing electrical tape to wrap the entire Arduino board and put it into a flush-mounted box behind the thermostat.



![Schematic](schematic.png)



### Note for [Livolo thermostats](https://www.livolo.eu/c-4632899/livolo-thermostat/)



In short, damn them! 😡



1. Livolo's 1-Wire master has non-standard timings and reads only the first 2 bytes of the entire DS18B20's response. You'll need to patch [OneWireHub](https://github.com/orgua/OneWireHub)'s `OneWireHub_config.h` and `DS18B20.cpp` using the included [`livolo.patch`](livolo.patch). See also https://github.com/orgua/OneWireHub/issues/84.

1. (Still checking this point.) Supposingly, one has to solder out the second sensor deep inside the thermostat **even before turning it on for the first time**. If you've already done that, you may try to figure out the calibrated temperature offset that the thermostat has calculated and remembered. Wait ~4 minutes and note the difference between displayed and real ambient temperatures. Then, change `livoloOffset` in the source code to compensate this.