***Question***

I2C device reading writing errors problem. How to solve it?

***Answer***

There are many reasons causing reading and writing errors.  To name a few: 

 1. Wires too long (more than 30cm) and not twisted.  A suggestion is to use twisted cable Cat 5 to reduce mains EMI noise picking up, 

 2. I2C speed too high. A suggestion it to start testing a low speed, such as 100kHz, 

 3. Pullup overloading Rpi which already has 1k8 pull up.  A suggestion is to remove ALL pullups of the I2C devices, 

 4. Rpi I2C circuit too noisy.  A suggestion is to use logical level converters such as TXS010n, TXB010n to step up 3V3 signal to 5V (high level means low risk of noise etc problem)
   
5. PSU dirty.  A suggestion is to place standard bypass/decoupling cpas 10u tantalum and 0.1 ceramic near the device and also near the Rpi mciro USB connector.  

[![rpi psu cap][1]][1]

*/ to continue, ...*

***Research Notes***

[Clean Power for Every IC, Part 1: Understanding Bypass Capacitors - Robert Keim, AAC 2015sep21][2]


[Clean Power for Every IC, Part 2: Choosing and Using Your Bypass Capacitors - Robert Keim. AAC 2015sep27][3]


> ***Introduction***
> 
> It is not inconceivable that a dedicated, successful engineering
> student would graduate from college knowing almost nothing about one
> of the most pervasive and important components found in real circuits:
> the bypass capacitor. Even experienced engineers may not fully
> understand why they *include **0.1 µF** ceramic capacitors next to every
> power pin of every IC in every circuit board they design.* This article
> provides information that will help you to understand why bypass
> capacitors are necessary and how they improve circuit performance, and
> a follow-up article will focus on details related to choosing bypass
> capacitors and the PCB layout techniques that maximize their efficacy.
> 
> ...
> 
> ***Solution***
> 
> it is convenient that such a serious problem can be effectively
> resolved with a simple, widely available component. But why the
> capacitor? A straightforward explanation is the following: A capacitor
> stores charge that can be supplied to the IC with very low series
> resistance and very low series inductance. Thus, transient currents
> can be supplied from the bypass capacitor (through minimal resistance
> and inductance) instead of from the power line (through comparatively
> large resistance and inductance). To better understand this, we need
> to review some basic concepts related to how a capacitor affects a
> circuit.
> 
> First, though, a brief note about terminology: The components
> discussed in this article are regularly referred to as both “***bypass***
> ***capacitors***” and “***decoupling capacitors***.” There is a subtle distinction
> here—“decoupling” refers to reducing the degree to which one part of a
> circuit influences another, and “bypass” refers to providing a
> low-impedance path that allows noise to “pass by” an IC on its way to
> the ground node. Both terms can be correctly used because a
> bypass/decoupling capacitor accomplishes both tasks. In this article,
> however, “bypass capacitor” is favored in order to avoid confusion
> with a series decoupling capacitor used to block the DC component of a
> signal.
> 
> ***A Standard Approach***
> 
> The foregoing analysis helps us to understand a classic bypassing
> scheme: 
> 
> ***a 10 µF capacitor within an inch or two of the IC,*** and 
> 
> ***a 0.1 µF ceramic capacitor as close to the power pin as possible***:
> 
> The larger capacitor smooths out lower-frequency variations in the
> supply voltage, and the smaller capacitor more effectively filters out
> high-frequency noise on the power line.
> 
> If we incorporate these bypass capacitors into the 8-inverter
> simulation discussed above, the ringing is eliminated and the
> magnitude of the voltage disturbance is reduced from ***1 mV to 20 µV***,
> ...


  [1]: https://i.sstatic.net/GwW5n.jpg
  [2]: https://www.allaboutcircuits.com/technical-articles/clean-power-for-every-ic-part-1-understanding-bypass-capacitors/
  [3]: https://www.allaboutcircuits.com/technical-articles/clean-power-for-every-ic-part-2-choosing-and-using-your-bypass-capacitors/