# How to use the 1-WIRE bus on Acqua SOM

<abstract>
This article illustrates how to enable a bit banging 1-wire bus on any Acqua GPIO pin
</abstract>

1-Wire is a device communications bus system designed by Dallas Semiconductor 
that provides low-speed data, signaling, and power over a single signal. 1-Wire is similar in concept to I2C, 
but with lower data rates and longer range. 

1-Wire is typically used to communicate with small inexpensive devices 
such as digital thermometers and weather instruments. This article illustrates how to 
read a popular DS18B20 thermal sensor.

## The Dallas/Maxim DS18B20 thermal sensor

<a href="http://www.maxim-ic.com/datasheet/index.mvp/id/2812"><img src="DS18B20.jpg" width="640px"/></a>

The DS18B20 digital thermometer provides 9-bit to 12-bit Celsius temperature measurements. 
It communicates over a 1-Wire bus that by definition requires only one data line (and ground) 
for communication with a central microprocessor. 

It has an operating temperature range of -55&deg;C to +125&deg;C and is accurate to &plusmn;0.5&deg;C over 
the range of &deg;10&deg;C to +85&deg;C. ([read more on datasheet](https://datasheets.maximintegrated.com/en/ds/DS18B20-PAR.pdf)).

## Wiring

| DS18B20  | Berta D2 Board |
|----------|----------------|
| 1 - GND  | GND            |
| 2 . Data | PB5            |
| 3 - Vcc  | 3V3            |


<div class="alert alert-danger" role="alert" markdown="1">
<span class="glyphicon glyphicon-info-sign" aria-hidden="true"></span>
A 4.7kOhm pull-up resistor is requested between the Data and Vcc pins
</div>

We are using PB5 line just for example but any GPIO line can be used.

## Install the kernel drivers

To enable the Kernel drivers (master and slave) follow this tutorial: 

* @h1='compile_kernel_5_15'. 

Using this command:

	make arch=ARM menuconfig

and enable the Dallas 1-wire support and the Thermal family implementation as shown below:

	Device Drivers  --->
	    <*>   Dallas's 1-wire support
	    	1-wire Bus Masters  --->
	    		<*> GPIO 1-wire busmaster
	    	1-wire Slaves  --->
	    		<*> Thermal family implementation

## Configuring the kernel driver using the device tree

Edit the device tree source available on <code>arch/arm/boot/dts/acme-acqua.dts</code> of your kernel tree 
and add these lines inside the <code>apb</code> section:

	onewire_0: onewire_0 {
		compatible = "w1-gpio";
		gpios = <&pioB 5 GPIO_ACTIVE_HIGH>;
		pinctrl-names = "default";
		pinctrl-0 = <&pinctrl_onewire_0_default>;
		status = "okay";
	};
		
then add also these lines in the section <code>board</code>: 

	pinctrl_onewire_0_default: onewire_0_default {
		atmel,pins = 
			<AT91_PIOB 5 AT91_PERIPH_GPIO AT91_PINCTRL_NONE>;
	};

It is possible to change PB5 with the GPIO you intend to use):

Changing the gpio parameter you can change the GPIO to use as 1-wire bus	

Any GPIO can be used as 1-wire bus. The pin used depends by
the device tree definition


## Read the temperature

The 1-wire driver automatically scans every 10 seconds if new sensors are plugged on the 1-wire bus.

For each 1-wire device detected a new directory is created on <code>/sys/bus/w1/devices</code>.

Type:

	ls /sys/bus/w1/devices/
	
	28-000005970839  w1_bus_master1
	
a thermal sensors has been found and their unique ID is <code>28-000005970839</code>.

To read the temperature from each sensor type:

	cat /sys/bus/w1/devices/28-000005970839/w1_slave
	3f 01 4b 46 7f ff 01 10 7a : crc=7a YES
	3f 01 4b 46 7f ff 01 10 7a t=19937

<code>t=19937</code> indicates that the temperature read is 19.9 &deg;C 

## Read the temperature each seconds in Python3

	#!/usr/bin/python3
	
	import os
	import time
	
	w1path = "/sys/bus/w1/devices/w1_bus_master1"
	
	# Extract the sensor id
	
	if not os.path.exists(w1path): 
		print ("1-wire bus not found")
		print ("Check if the 1-wire bus is installed")
		exit(1)
	
	deviceList = os.listdir(w1path)
	
	# for deviceId in deviceList:
	#	print(deviceId)
	
	onewire_id=[deviceId for deviceId in deviceList if deviceId[0:2]=="28"]
	
	# print(onewire_id[0])
	
	
	# Read temp
	
	
	while True:
		f = open("/sys/bus/w1/devices/" + onewire_id[0] + "/w1_slave","r")
		tString=f.read()
		f.close()
	
		if tString.find("NO")>=0:
			print ("Wrong CRC")
			exit(1)
						
		p=tString.find("t=")
		value =float(tString[p+2:-1])/1000
		formatted_value = "{:.2f}".format(value)
		print(formatted_value)
	
		time.sleep(1)

### Download

* [acme-acqua.dtb](./acme-acqua.dtb) Ready to use Device tree blob file to enable PB5 line as 1wire. Save this file
inside the first partition microSD and reboot.
* [acme-acqua.dts](./acme-acqua.dts) Device tree source used
* To compile the device tree blob from source follow this article @article='compile_kernel_5_15'

##Links

* [DS18B20 datasheet](https://datasheets.maximintegrated.com/en/ds/DS18B20-PAR.pdf)
* [Wikipedia 1-Wire definition](http://en.wikipedia.org/wiki/1-Wire)
* [Previous version of this article for Kernel 4.19](/acqua_1wire_419)

@include='bio_tanzilli'