[PD] Sensors GPIO Raspberry Pi Pd

Julian Brooks jbeezez at gmail.com
Sun Apr 7 23:42:16 CEST 2013

Thanks Martin, really useful stuff.

I've got i2cdetect on the RPi which is how I knew that [gpio] was setting
hi & lo.  And good to hear you'll be wrestling with this on the Pi as well.

In some ways this is good news as we've setup everything from the
'instructables' page already and now just need to get the bloody thing
going (have to to sort the housings out).

Another possible issue is that from my reading it seems that the RPi
doesn't do 'clock-stretching', though I have found a link where they slow
the i2c bus down.

Another one here too:

That's interesting as they talk about setting up more GPIO pins for i2c to
run 2 sensors.

Not being able to change the sensors address is a real pain though, as one
of the things that I keep reading about i2c is it's ability to run up to
128 sensors on the same line - kinda defeats the object!  Must be a way
round it.

"You can use the 5V from the GPIO header on the pi. From the schematic pin
2 is 5V. Ground is on pin 6. Pin 3 is the i2c data and pin 5 is the clock.
Pullup resistors are already installed on those lines."

Yes, found a good diagram for the GPIO schematic.

My understanding was that what we can't do is send data from the sensor at
5v back into the RPi at 3.5v and it's there that we need to drop the
voltage back to 3.5.  Noticeably though the 'instructables' link says they
just did it anyway and was fine (with a disclaimer attached on to it).

We got some 4.7k resistors as you recommended - do we only need these
before the sensors?  The pdf from digikey has a diagram with a voltage
transformer that we've been presuming is what we need to do?? Presumably if
we put more resistors next to the Pi then we wont have enough voltage to
lift the pin high (many ???).  There's also lots of code (C?) on that pdf,
anything you've made use of?

This is the little add-on board
I did read it's doable with mos-fet but seemed like another layer where we
can screw-up so have taken the simple option.

Still don't get how we tie in the clock and the messages but I'm sure it'll
become clearer when we actually get to the point where we can start it up.



On 7 April 2013 14:28, Martin Peach <martin.peach at sympatico.ca> wrote:

> Also check this out: it seems to have everything except how to make a pd
> external from it.
> http://www.instructables.com/**id/Raspberry-Pi-I2C-Python/<http://www.instructables.com/id/Raspberry-Pi-I2C-Python/>
> Martin
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