Hardware » Cablemeter

h1. Eval

h1. Overall design

* 4 x red+green LEDs for condition
* Restart button
* Rotate over the ADC channels and get Voltage level
* draw 100mA
* Die Kabel haben AWG28, 212.9 Ohm/km, 1.4 A nach erde, 0.23 A versorgung
* 0,2129 Ohm/m; 1,0645 Ohm/5m; 2,129 Ohm/10m;
* https://de.wikipedia.org/wiki/E-Reihe#/media/Datei:E12_values_graph.svg

U2=((U*R2)/R_GES)

U
R*I

5V/0,1A= 50 Ohm
5V*0,1A= 0,5 W

5V/0,5A= 10 Ohm

RGes = R1+R2 = 50

3V=(5*R2)/50
R2 = (3*50)/5 = 30 -> 27
R1 = 22
RGES = 49

U2 = 5*27/49 = 2,755102

theoretically an device that draws 0,1A and 5m:
U2=((5*50)/ (50+1,0645) ) = 4,8957691; that should work

theoretically an device that draws 0,5A and 10m:
U2 = ( (5*10) / (10+2,129) ) = 4,1223514 V



h1. MCU

* "stm32f051c4":https://www.mouser.de/datasheet/2/389/stm32f051c4-1851079.pdf
** I have 17;
** 16 ADC channels
* STM32G030C8T6
** nearly same specs but smaller footprint; LQFP 48
** 2,68€ inc. Mwst.