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@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
Could be useful


On 25 April 2013 15:54, Martin Peach <martin.peach@sympatico.ca

<mailto:martin.peach@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