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Topic: resistor noob (Read 747 times) previous topic - next topic

kmkn



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 ?
http://malaysiascada.blogspot.com/

fungus

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

kmkn

I am sure my measurement using multimeter was correct
http://malaysiascada.blogspot.com/

strykeroz

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?
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fungus

#4
Mar 27, 2013, 12:43 pm Last Edit: Mar 27, 2013, 12:46 pm by fungus Reason: 1

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?

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

kmkn

Voltage after the resistor or at the pin. Ampere before resistor or near sensor device. Did i did my wiring wrong?
http://malaysiascada.blogspot.com/

kmkn



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?
http://malaysiascada.blogspot.com/

liudr

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.

fungus


Really strange here. What are you measuring?


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

kmkn


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
http://malaysiascada.blogspot.com/

JimboZA

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.
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No PMs for help please.
DO NOT power servos from Arduino 5V: give them their own power and connect the grounds.

PedroDaGr8

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).


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