Eval¶

Overall design¶

• 4 x red+green LEDs for condition
• Restart button
• Iterate over the ADC channels and get Voltage level
• Self-Calibrating via MOSFET (shortcuit cable interface)
• draw 100mA. Why? Sonst habe ich keinen Spannungsteiler. Je mehr Strom desto hoeher der Spannungsabfall; optional via mosfet.; 3/0,1= 30 Ohm
• ADC loesst theoretisch auf "3 / 4096 = approx. 0,0007" Volt auf.
• 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
• Buzzer would be nice for indication; durchklingeln Da werde ich lieber Multimeter nehmen.
• PWM Output
• Pinsocket connected to wires to measure resistance/Voltage directly
• https://www.aeq-web.com/spannungsteiler-microcontroller-berechnen-und-dimensionieren/
• Spannungen einzeln schaltbar damit auch kurzschluesse detektiert werden koennen

Schema¶

3V
        |
       | |  Cable
        |-------------->ADC
       | | 30Ohm
        |
       ===

Theoretische Spannungen bei AWG28¶

theoretically an device that draws 0,1A, 5V and 5m AWG28 cable:
U2=((5*50)/ (50+1,0645) ) = 4,8957691; that should work

theoretically an device that draws 0,5A, 5V and 10m AWG28 cable:
U2 = ( (5*10) / (10+2,129) ) = 4,1223514 V

theoretically an device that draws 0,1A, 3V and 5m AWG28 cable:
U2=((3*30)/ (30+1,0645) ) = 2,8971978; that should work

theoretically an device that draws 0,1A, 3V and 10m AWG28 cable:
U2=((3*30)/ (30+2,129) ) = 2,8012076

theoretically an device that draws 0,25A, 3V and 10m AWG28 cable:
U2= (3 * 12) / (12 + 2,129) = approx. 2,547951

theoretically an device that draws 0,5A, 3V and 10m AWG28 cable:
U2= (3 * 6) / (6 + 2,129) = approx. 2,2142945
U2= (3 * 6,8) / (6,8 + 2,129) = approx. 2,2846903

Calculations I¶

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

Calculations II¶

• Ein Kabel >= 10m soll durchfallen. Koennen trotzdem groessere Wiederstaende verwendet werden?

Ohne Widerstand:

U2 = 2,755102

Obige werte 1fach, 10m Kabel:

R2 = 27
R1 = 22
mit 10m
U2 = (5*27)/(49+2,129) = 2,6403802
2,755102-2,6403802=0,1147218
0,1147218/0,00073242188 = 156,6335

Obige werte 10fach, 10m Kabel:

R2 = 270
R1 = 220
mit 10m
U2 = (5*270)/(490+2,129) = 2,7431832

Bei 12Bit ADC: 3 / 4096 = approx. 0,00073242188 V pro ADC-Wert.
2,755102-2,7431832=0,0119188
0,0119188 / 0,00073242188 = approx. 16,273135. Thats not super much

Calculations III¶

Keyfeatures¶

• Cable checker
• Buzzer Durchgangspruefer
• PWM Output

MCU¶

• stm32f051c4
  • I have 17;
  • 16 ADC channels
• STM32G030C8T6
  • nearly same specs but smaller footprint; LQFP 48
  • 2,68€ inc. Mwst.
  • ADC faster
  • Mentions an 16Bit ADC value via oversampling, but thats complicated: adding white noise in order to calculate further 2 bits by software. Every MCU can do that.