I2C SCL clock problem - clock signal reduced (using DSO traces)

[gck303]

I am trying to get an ADS1110 voltage break out to work. The sample code does not work.

A few weeks ago the same code (Tutorial – Arduino and the TI ADS1110 16-bit ADC | tronixstuff.com) and breakout board worked. I needed to re-solder and reassemble my circuit and now it does not work.

Attached are a couple of DSO traces:

• The first trace shows the ADS board working, the second smaller trace when it does not work correctly.
• You can see that the arduino is sending the SCL and the ADS is returning a signal. So, I assume that the board is working and does not require replacement.
• I am not using a 4k7 pullup resistor, not a 10k. I ran out, but this does not seem to be affecting the signal.
• The arduino now only seems to be sending a single byte (8-ish) of SCL signals, and not the 50+ it did before.

What has happened? How to make it work?

Many thanks, George

[Koepel]

Everything you see in the second picture is by the Arduino. There is no one else on the bus.
At the begin and end is a START and STOP condition.
Between that are 9 clock pulses (a high level of SCL).
The first 7 pulses is to put the I2C address on the I2C bus. The Arduino is using the SDA for the I2C address. The 8th clock pulse is the R/W bit.
The 9th clock pulse is where the ADS1110 should pull the SDA low for a ACK. But it doesn't do that.

When the Arduino does not get a ACK after the I2C address, then it assumes that it is not there. The Arduino does not send data anymore, only the STOP condition.

Run a I2C Scanner sketch. Try to make it work by checking all the wires. The ADS1110 might be broken.

[gck303]

Thank you very much. That is very helpful.

I have checked the soldering/wiring and it is still not working. I have ran a I2C bus scanner, and it is not showing the ADS1110 at address 0x48, so I think it might be broken.

I will report back when the replacement arrives and is fitted.

[gck303]

Thank you again. The fault ADC was exactly the problem. I replaced it and it now works.

Best wishes, George

[Koepel]

Thanks for letting us know. I'm glad it is working
The pictures helped a lot to find to the cause.

I'm a big fan of the LHT00SU1 with sigrok/PulseView. Scrolling through data and decoding data is so much more easier on the computer.
https://www.banggood.com/Geekcreit-LHT00SU1-Virtual-Oscilloscope-Logic-Analyzer-I2C-SPI-CAN-Uart-p-988565.html.

I hope you don't get too excited about the I2C bus. I wrote this to scare new users: How to make a reliable I2C bus · Koepel/How-to-use-the-Arduino-Wire-library Wiki · GitHub.