Pages: [1]   Go Down
Author Topic: resistor noob  (Read 693 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Newbie
*
Karma: 0
Posts: 34
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset



Hi,
 picture above is what we done... we test it using multi-meter v=2.64 i=12.8 r=470

The question ...why dosen't it follow the v=ir ?
Logged


Valencia, Spain
Offline Offline
Faraday Member
**
Karma: 150
Posts: 5649
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Measurement error.
Logged

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

Offline Offline
Newbie
*
Karma: 0
Posts: 34
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

I am sure my measurement using multimeter was correct
Logged


Brisbane, Australia
Offline Offline
Edison Member
*
Karma: 33
Posts: 1123
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I presume your I value is in milliamperes so should actually be 0.0128A for I in the equation leading to V=6V ?

Can you explain where each of those measurements were taken?
Logged

"There is no problem so bad you can't make it worse"
- retired astronaut Chris Hadfield

Valencia, Spain
Offline Offline
Faraday Member
**
Karma: 150
Posts: 5649
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I am sure my measurement using multimeter was correct

I'm not saying you copied the numbers down incorrectly, I'm saying that maybe your multimeter isn't good at measuring this, maybe the current flowing isn't constant, etc.

The alternative is that the laws of the universe are wrong. Which do you think is more likely?

« Last Edit: March 27, 2013, 06:46:25 am by fungus » Logged

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

Offline Offline
Newbie
*
Karma: 0
Posts: 34
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Voltage after the resistor or at the pin. Ampere before resistor or near sensor device. Did i did my wiring wrong?
Logged


Offline Offline
Newbie
*
Karma: 0
Posts: 34
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

I am sure my measurement using multimeter was correct

I'm not saying you copied the numbers down incorrectly, I'm saying that maybe your multimeter isn't good at measuring this, maybe the current flowing isn't constant, etc.

The alternative is that the laws of the universe are wrong. Which do you think is more likely?


My arduino reading is also the same. So i thought mybe my wiring is wrong?
Logged


Central MN, USA
Offline Offline
Tesla Member
***
Karma: 74
Posts: 7255
Phi_prompt, phi_interfaces, phi-2 shields, phi-panels
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Really strange here. What are you measuring? I saw a resistor but how is it connected into the circuit and why is this measurement even related to arduino, just because it is photographed?

What is the unit of the current? Have you measured currents before? It's different from measuring resistance or voltage.
Logged


Valencia, Spain
Offline Offline
Faraday Member
**
Karma: 150
Posts: 5649
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Really strange here. What are you measuring?

He didn't say.
Logged

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

Offline Offline
Newbie
*
Karma: 0
Posts: 34
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Really strange here. What are you measuring? I saw a resistor but how is it connected into the circuit and why is this measurement even related to arduino, just because it is photographed?

What is the unit of the current? Have you measured currents efore? It's different from measuring resistance or voltage.
Miliampere. Arduino reading from analog pin about 400..i just read the device manual it has current output, passive ouput ,and active output. I connect to current output but maybe i should connect to passive output
Logged


Johannesburg. UTC+2
Offline Offline
Faraday Member
**
Karma: 105
Posts: 4681
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I don't think anyone trying to help here, is actually sure of what you've tried to show in the photo or what / where / when you're trying to measure.

I suggest you make a sketch of the circuit and show clearly where and when you are taking the measurements. As liudr said above, measuring current is different: he was (I think) hinting that you need to realise you have to break the circuit to measure current with your meter in series and measure current in the circuit as opposed to voltage across a component.
Logged

The Elders of the Internet know who I am
I'm on LinkedIn: http://www.linkedin.com/in/jimbrownza

San Diego, CA
Offline Offline
Jr. Member
**
Karma: 1
Posts: 66
A sociable geek chemist
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I can see the resistor but I am not sure what its doing, how its doing it etc.

While several members have said measurement error, its about as useful as saying car won't start you need to fix it. The problem is they don't have enough information to tell you WHAT is wrong, just the end result.

You don't mention how you measure:
resistance - was the resistor still in circuit (any voltage present will throw off the reading)
voltage - is the voltage source strictly DC, is it PWM DC, is it an AC signal with DC component etc. these can have dramatic affects on the readout voltage.
Current - did you place your multimeter in-line with the device or did you try measuring voltage drop across said resistor (assuming its inline with the current you want to measure).

Logged

Pages: [1]   Go Up
Jump to: