I2C drive capability

Use a lower datarate. And/or use linedrivers.

I2C was never design to drive 5 Meters of anything !!!

Yes, find a driver chip, or isolate the cables from the relay board with a simple transistor driver.

hamilton

thanks, all, for the advice. I'll try to set up a line driver.

Or use 1-Wire temp sensors.

Considering the relay board runs from 5V I should imagine you have all sorts of issues with cable runs causing voltage drops and the 5V thresholds for I2C input not being met.

Without more details on how setup, and how many pull up resistors you have left in and what devices and pull up resistors are connected to very difficult to get a definitive solution.

There are many possibilities.

I have run 5V I2C successfully with line driver over 12m for acquisition equipment running for days.

Please remember the Pi I2C is 3V3, so check the I2C input thresholds for high and low can be met with the setup you want. Remember the cables if not good enough you will have a series resistor affetcting both thresholds.

And you use them at 15+ feet ? At what frequency ?

How often do you read them ?

once a second, once a minute ?

Try dropping the data rate. If you have wiringPi installed, then unload the I2C drivers - use lsmod then rmmod, then

gpio load i2x 10

will load it at 10Kbps. (Default is 100Kbps) Give it a go then.

Gordon

If it's this one:

then it's designed to run on the Pi at 3.3v It has an mcp23017 running at 3.3v that talks I2C on one side, and feeds into a ULN2803 at the other side to drive 4 relays and provide 4 spare open collector outputs.

The Pi's I2C bus has on-board 1K8 pullups to 3.3v

Gordon

I have four spaced at about 3 ft intervals after 10 ft plus of cable. They ought to work on cables up to 300+ m long (1000 ft), though I suspect you may be limited to the number of devices, where they are along the cable and be unable to reliably use the parasitic power. Still two pair telephone cable is cheap (or CAT5) to get the three required wires (data, ground, +V).

If you mean the data rate over the bus around 16 kbit/s.

I cheated and bought a Embedded Systems OW Server. That polls all the sensors at roughly 5 second intervals, provides a basic web interface to that data and can push the data as XML over ethernet.

It's is possible for a Pi to talk to 1-Wire devices directly, IIRC there are a few libraries for that.

On 24/12/2013 10:47, Dave Liquorice wrote: []

You recall correctly, here's a very simple example:

Consistent with rPi's minimalist approach: i2c seems very interesting. Where would I find the docos for the apparently existing rmmod gpio load 12x 10 notation/syntax, to start some experiments, with minimal initial effort?

That notation seems to imply that we have access to existing rPi software to simply, eg. connect 2 rPis via i2c. Is that right? Also the 3.3v 5v incompatibility wouldn't be a problem? OTOH I can't remember what I read: does i2c do peer-to-peer or only master-slave/s?

==TIA.

man rmmod man gpio