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Re: [LUG] WiringPi - 1 Wire?


On Thu, 16 Feb 2017, Tremayne, Steve via list wrote:


You get a higher quality reply if you email me directly rather than via the list ;-)

  I was "fiddling" with a Ras Pi Zero and a 1-wire temp sensor yesterday...

Does your Wiring Pi deal with 1-wire? I got no search results from the site, so I'm presuming not?

1-wire is handled very well by the Linux kernel and its owfs (one-wire filing system), so there's no need for me to write anything for something that's already there.

However, for the common ds18b20 1-wire temperature sensors, I've created a pin wrapper for them to better integrate them into the wiringPi world.

You'll need to install the latest wiringPi from source though.


then run:

  sudo raspi-config

go through the menus and enable 1-wire. Plug in the sensor - it's fixed to bcm_gpio pin 4 (physical pin 7) then

  ls /sys/bus/w1/devices

If you see a 28-????? file, then the ds18b20 is present. You can cat this file/w1_slave - e.g.:

  $ cat /sys/bus/w1/devices/28-0000053af458/w1_slave
  f6 00 4b 46 7f ff 0a 10 d6 : crc=d6 YES
  f6 00 4b 46 7f ff 0a 10 d6 t=15375

your filename will be different from mine - each device has a unique 64-bit ID and mine is: 0000053af458.

In the output above, YES means a good read and t=15375 is the temperature times 1000. Remember these are +/- 1°C devices, so round and truncate appropriately.

With the latest wiringPi:

  $  gpio -x ds18b20:100:0000053af458 aread 100

means 15.4°C.

In a C program:

  #include <ds18b20.h>

  int temp10 ;
  if (ds18b20Setup (pinBase, "0000053af458") < 0)
    .. something went wrong  exit (1) ;
  temp10 = analogRead (pinBase) ;

returns the temperature times 10 as an integer.

Reading takes about 3/4 a second.

It's been a while since I've really done much "fiddling" with electronics, so I'm finding more rust on my brain than I thought - so, if 1-wire is handled by I2C / SPI, then apologies... I'll just go and RTFM...

It's handled directly. Use BCM_GPIO pin 4 and off you go.

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