Re: [beagleboard] Re: Issue getting DS18B20 temperature sensor working

[Josenivaldo Benito Junior]

On Sun, Sep 7, 2014 at 4:14 PM, Michaël Vaes vaesmich...@gmail.com wrote:
 Is there any way to see the RAW inputs/outputs on a pin?

I would use a logic analyzer to see if the communication is going
well. I have one of this: https://www.saleae.com/ but of an old model
(maybe you still can get clones from eBay), it is very useful to debug
I2C, 1-wire and and other protocols or simple input/output.

If there is 1-wire comm going on the Pin you will be able to catch or
if not you will be able to see were it is failing.

A oscilloscope can also help to see if pin is swinging during transmissions.

BR
--
Josenivaldo Benito Jr.
PU2LBD

*Por Aurélio Buarque de Hollanda,  elite, do francês élite, significa
“o que há de melhor em uma sociedade, minoria prestigiada, constituída
pelos indivíduos mais aptos”.

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Re: [beagleboard] Re: Issue getting DS18B20 temperature sensor working

[Josenivaldo Benito Junior]

Hi Michaël,

Are you using 18ohm pull up resistor as your wiring diagram states? If so
this resistor is too low for pull up; both bone and sensor will have to
sink a lot of current to drive the line down.

See this discussion here:

https://groups.google.com/forum/#!topic/beaglebone/dosKmEE7xso

Gerald told a beaglebone pin can sink around 6mA, but using Ohm's Law to
find current over a 18ohms resistor while driven by 3.3V voltage source we
find 0.183A or 183mA. The discussion pointed above talk  about 1K resistor,
this would result in 3.3/1000 = 0.0033 or 3.3mA.

Your beaglebone and sensor might have not enough strength to hold the Data
line down (GND) and because of this there is no communication. This also
can damage the bone pin, so for test try another pin with 1k resistor pull
up.

Regards,
Benito

On Sat, Sep 6, 2014 at 10:10 AM, Michaël Vaes vaesmich...@gmail.com wrote:

 Changing the OS to Ubuntu did not change the behaviour.
 Any help is appreciated on debugging this.

 Thanks!
 *Michael*


 On Saturday, August 30, 2014 1:01:18 PM UTC+2, Michaël Vaes wrote:

 Hi -

 I'm stuck getting my DS18B20 temperature sensor working on my Beaglebone
 Black.  I installed and loaded the DTC overlay but Im not getting the '28-*'
 files in my '/sys/devices/w1_bus_master1/' directory.

 *Wiring*
 https://dl.dropboxusercontent.com/u/97513059/ds18b20-
 temperature-sensor.pdf





--
*Josenivaldo Benito Jr.*
*PU2LBD*

*Por Aurélio Buarque de Hollanda,  elite, do francês élite, significa “o
que há de melhor em uma sociedade, minoria prestigiada, constituída pelos
indivíduos mais aptos”.

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