[PD] Sensors GPIO Raspberry Pi Pd

Julian Brooks jbeezez at gmail.com
Mon Apr 29 23:44:49 CEST 2013

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
There's this one:
which is 86p each.
Or there's something like this:
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?



On 29 April 2013 16:38, Martin Peach <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@**sympatico.ca <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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