If they relied on the internal pull up in the uC it may not be good. There are some white paper out there and it basically said the internal pullup are not good for i2c, FWIW.
-Jerry > On Mar 9, 2015, at 2:07 PM, Greg Peek <[email protected]> wrote: > > Have you looked at the signal quality of the I2C (working with 6 boards) with > a ~100MHz scope? 6+ loads on i2c needs a stronger pull-up than 10K. > > I like the antenna idea. Maybe try shielded cables to the POTs, or "big" > caps. Who cares how slow the pot voltage changes, right? > > > > Input leakage would explain the unconnected analog pins going to Vcc. Does a > 100K to ground pull them low (just as a test). > > On Mon, Mar 9, 2015 at 1:32 PM, Jerry Biehler <[email protected]> wrote: > Might put some small caps between the pot signal wire and the ground to kill > noise. They might be acting like giant antennas. > > You also could try stronger pull-ups on the i2c. > > -Jerry > > > On Mar 9, 2015, at 1:24 PM, Jim Larson <[email protected]> wrote: > > > > Following is a description of a problem I'm having in a motor control > > system I'm working on down here in Sunny San Diego. Any thoughts or > > insights would be most appreciated. > > > > I have 8, 10K linear pots. The wiper of each pot is tied to an analog input > > of an Arduino Mega (Analog pins 0 to 7). One end of each pot is tied to the > > 5V rail; the other to ground. The pots are located 3 to 8 feet from the > > Arduino. I have a header for the power connections and another for the > > grounds. A wire from each header connects them to the 5V and GND > > connections on the Mega. There are 6 motor driver shields (ADFruit Motor > > Shield V2) stacked on the Mega and the header connections actually plug > > into the top one of these. My problem is that connecting the headers to the > > Mega with all the pots connected to the headers causes the motor shields to > > fail initialization. When I connect the headers with only 6 (maybe 7) pots > > connected, works fine. If I connect the last one or two pots, it fails. If > > the two headers are not connected, all is well. Motor boards initialize > > just fine. If I connect even the ground header(!), the initialization > > fails. By fails, I mean that somewher e > in the initialization of the very first board, the driver code hangs. I have > not yet tried to find exactly where the driver code hangs - I don't think > that's where the problem lurks. > > > > Voltages measure just fine. That is, the Arduino rails measure 4.99V > > between them with the headers connected or not connected. Using an external > > supply to drive the Arduino doesn't change anything. I'm considering an > > independent 5V supply for the pots, but I'm not convinced that will solve > > the problem (since I don't know what the problem is.) > > > > Resistance between the headers measures about 1.3K - what you'd expect for > > 8, 10K resistors in series. > > > > One possible clue: the motor shields use I2C for all control. That could be > > my "canary". > > > > Something that bothers me: There is a measurable voltage on the headers > > when they are not connected to power and ground. (4.99V). Since the wires > > only connect to each end of the pots and should not be connected to the > > circuitry otherwise, I don't know why this voltage should exist. The wipers > > of the pots are connected to the Analog pins of the Arduino Mega. I am > > assuming that these are configured as inputs by Arduino and should not be > > sourcing any voltage, right? So where is the voltage coming from? Is it > > induced by voltages elsewhere in the system? The resistance measurement > > does not indicate a short anywhere. > > > > > > --- > > This email has been checked for viruses by Avast antivirus software. > > http://www.avast.com > > > > _______________________________________________ > > dorkbotpdx-blabber mailing list > > [email protected] > > http://music.columbia.edu/mailman/listinfo/dorkbotpdx-blabber > > _______________________________________________ > dorkbotpdx-blabber mailing list > [email protected] > http://music.columbia.edu/mailman/listinfo/dorkbotpdx-blabber > > _______________________________________________ > dorkbotpdx-blabber mailing list > [email protected] > http://music.columbia.edu/mailman/listinfo/dorkbotpdx-blabber _______________________________________________ dorkbotpdx-blabber mailing list [email protected] http://music.columbia.edu/mailman/listinfo/dorkbotpdx-blabber
