[PD] Sensors GPIO Raspberry Pi Pd

Martin Peach martin.peach at sympatico.ca
Tue Apr 30 00:05:48 CEST 2013

Ordinary 5% resistors will work fine. Probably anything from 1k to 100k 
would work. Most likely you have a loose connection somewhere. Did you 
try running the bus at a lower speed? If your wiring is long (> 10cm) 
it may be better to run it slower.


On 2013-04-29 17:44, Julian Brooks wrote:
> Hi Martin / all,
> Possibly overly-nerdy question here:
> I'm buying the various bits and pieces we require for the multiplexer
> and I'm noticing quite a difference in pricing options for the pull-up
> resistors.
> There's this one:
> http://uk.farnell.com/welwyn/rc55-10k-0-1/resistor-10k-250mw-0-1/dp/9499938
> which is 86p each.
> Or there's something like this:
> http://uk.farnell.com/multicomp/mcf-0-25w-10k/resistor-10k-250mw-5/dp/9339060
> which is 2p each.
> The former's spec sheet talks about its very low noise ratio and
> thinking on from reading the sensors spec sheet it's also pushed there
> to use low-noise components.
> Do you think it actually makes any difference?  I have to buy a minimum
> 50 of the cheap ones so buying a couple of the dearer ones doesn't
> actually make much of a difference.
> It got me thinking as you mentioned that your getting virtually no PEC
> errors from the sensors whereas as we are getting them very regularly.
> I had been thinking it was the soldering of those pernickety sensors but
> could it also be the cheap 4k resistors currently on our board?
> Cheers,
> Julian
> On 29 April 2013 16:38, Martin Peach <martin.peach at sympatico.ca
> <mailto:martin.peach at sympatico.ca>> wrote:
>     Here's a patch to display data from two D6T sensors on the same I2C
>     bus. The clock line is switched using a 4051 analog multiplexer. The
>     control line is GPIO_17 of the Pi connected to A of the 4051 (B, C
>     and Inhibit are at 0V). 10k resistors to 3.3V are on each sensor's
>     clock line at X0 and X1 of the 4051 (I2C clock connects to X).
>     Because the code accesses the GPIO file system it needs to be run as
>     root. I have two different sensors so the code reads two different
>     packet lengths. Just a proof of concept, there could be up to 8
>     identical sensors on the same bus with this setup.
>     Martin
>     On 2013-04-25 20:04, Julian Brooks wrote:
>         Just spotted this:
>         https://github.com/kadamski/__i2c-gpio-param
>         <https://github.com/kadamski/i2c-gpio-param>
>         Could be useful
>         On 25 April 2013 15:54, Martin Peach <martin.peach at sympatico.ca
>         <mailto:martin.peach at sympatico.ca>
>         <mailto:martin.peach at __sympatico.ca
>         <mailto:martin.peach at sympatico.ca>>> wrote:
>              On 2013-04-25 10:37, Julian Brooks wrote:
>                  'Nother 2 dumb questions:
>                  What's the difference between the ones that have
>                  spider/centipede type
>                  legs and the straight ones (which would be best to get).
>              The PDIP package is what you want, not the SOIC. The only
>         difference
>              is size. DIP packages are human-friendly, surface mount is
>         for robots.
>                  And also are you attaching the MC14051 to any type of
>                  board/adaptor or
>                  just soldering straight on to the pins?
>              I have it in a breadboard right now, to make it more
>         permanent I
>              would solder a socket to a prototyping board then (after
>         verifying
>              the connections) plug the chip into the socket. Soldering
>         to the
>              pins makes it difficult to replace the IC, and risks
>         damaging it
>              with the heat if you're not good at soldering quickly and
>         to the
>              point. A CD4051 would also work, it's basically the same
>         circuit.
>              Martin

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