Cable matters !

I just want to share what I examined yesterday...

Background:

I used OPi one to output HDMI video when a button is pressed. It has an attached fan, a remote shutdown button and a remote switch to turn power off-on (OPi is hidden and operated through these buttons). It worked on breadboard, produced 2 working examples, tested the first two with a 24h test. All fine...

Problem:

On a third installation after the "circuits" are built, I made a last test. HDMI output had problems  Sound comes and goes with a hick-up...

Debugging:

Checked wiring, checked with other video, checked with other OPi etc. Nada... The problem persisted.

Lastly I checked the voltages. The output from the 2A power supply is 5.3V, (it goes to the switch and comes back) and the input to OPi is about 4.7-4.8 V !!!!!

What the heck...

I measured the full two way resistance of the power switch "circuit" as 1.2 Ohms. Well, not much

Ohms law does not say so. Opi amperage is around 0.3-0.55 A in my application depending on video usage.

Assuming 5 V and 0.5 A, the voltage drop on 1.2 Ohms line is 0.6 volts. Huh, this makes it 4.7 V on OPi... 

Knowing possible issues beforehand I used quality 23 AWG full copper FTP CAT6 cables for data lines, but just used simple 2x1.5mm2 power cable - a 5.4 mt long two way trip. But it was not the problem either... Measured the switch, measured the 5.4 mt cable... But:

I used some cheap jumper cables (which I ordered from China), and connected the switch to a protoboard with them (easy to solder and plug), and those 2x20 cm cables had a huge resistance... 

I connected the switch with a thick cable and voila, the voltage at OPi is 5.0 V...

Other installations did not have this issue because the wire lengths were now so high.

Just wanted to share for those having issues... Bad voltage may manifest itself in very different ways.

Actually, the most problematic part while working with *Pi's is usually the USB power cable quality. What happens to your phone (did I hear you complain on slow charging?) also happens here. In my experience a simple SMPS with 2A rating usually works well in those amperage, but cheap power cables suck !

Did we get through all our copper resources on this planet? Damn!