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Topic: measure a resistor? (Read 1 time) previous topic - next topic

cjdelphi

Measuring how many ohms?

5v ~~~~ 1k ~~~~ A0

sure i get a voltage reading... but how many ohms? Cheers

James C4S

Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

Goofballtech

http://arduino.cc/forum/index.php/topic,21614.0.html

marco_c

#3
Sep 14, 2012, 05:56 am Last Edit: Sep 14, 2012, 06:16 am by marco_c Reason: 1
You already have the ohms written down as 1k ohm
Arduino Libraries http://arduinocode.codeplex.com
Parola for Arduino http://parola.codeplex.com

Goofballtech


cjdelphi

Cool... a 2nd resistor's required.... cheers

marco_c

How do you propose to use this second resistor to measure resistance?
Arduino Libraries http://arduinocode.codeplex.com
Parola for Arduino http://parola.codeplex.com

danb35


How do you propose to use this second resistor to measure resistance?

Simple voltage divider.  5V -> R1 -> analog input on arduino -> R2 -> ground.  Given the voltage reading at the Arduino and the value of one of the resistors, the value of the other can be calculated.

CrossRoads

Voltage divider: Vin - R1 -Vout-R2- Gnd
Vout = Vin *R2/(R1+R2)
Do some rearranging:
Vout(R1+R2) = Vin*R2
VoutR1 + Vout R2 = VinR2
VoutR1 = VinR2 - VoutR2
VoutR1 = (Vin - Vout)R2
VoutR1/(Vin - Vout) = R2

Ex: Vout 3V, Vin5V, R1=10K
3*10000/(5-3) = 15000

check Vout = Vin *R2/(R1+R2)
Vout = 5*15000/(10000+15000) = 3V
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

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