Pages: [1]   Go Down
Author Topic: measure a resistor?  (Read 922 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Edison Member
*
Karma: 29
Posts: 2441
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Measuring how many ohms?

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

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

Austin, TX
Offline Offline
Faraday Member
**
Karma: 71
Posts: 6146
Baldengineer
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Ohms Law
Logged

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

South Louisiana
Offline Offline
Full Member
***
Karma: 0
Posts: 178
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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

Sydney, Australia
Online Online
Edison Member
*
Karma: 33
Posts: 1270
Big things come in large packages
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

You already have the ohms written down as 1k ohm
« Last Edit: September 13, 2012, 11:16:31 pm by marco_c » Logged

Arduino libraries http://arduinocode.codeplex.com
Parola hardware & library http://parola.codeplex.com

South Louisiana
Offline Offline
Full Member
***
Karma: 0
Posts: 178
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

You already have th ohms written down as 1k ohm

 smiley-eek-blue
Logged

Offline Offline
Edison Member
*
Karma: 29
Posts: 2441
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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

Sydney, Australia
Online Online
Edison Member
*
Karma: 33
Posts: 1270
Big things come in large packages
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

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

Arduino libraries http://arduinocode.codeplex.com
Parola hardware & library http://parola.codeplex.com

Offline Offline
Full Member
***
Karma: 1
Posts: 107
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

Global Moderator
Boston area, metrowest
Offline Offline
Brattain Member
*****
Karma: 533
Posts: 26943
Author of "Arduino for Teens". Available for Design & Build services. Now with Unlimited Eagle board sizes!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

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
Logged

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Pages: [1]   Go Up
Jump to: