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Topic: analogRead with Potentiometer / Watt (Read 942 times) previous topic - next topic

Frank Burns

i found an example where a potentiometer was connected to
+5V, GND and A0 on a arduino uno.... i tryed the same, butt
my potentiometer (0,25W) died.
my question: do i need a potentiometer for more Watt or did
i made a  mistake in the circuit ?

thanks

JimG

I do this all the time using 10K pots.  Wattage is extremely small (way less than 1/8 watt).  So you must have either hooked it up wrong or used a too small resistance.

Make sure the wiper (usually pin 2 on the pot) is connected to the A0 pin and you can't really go wrong.

Jim
TC4 Open Source Digital Thermometer and Temperature Controller
http://code.google.com/p/tc4-shield


Frank Burns

i have to corr.my first post.
at the moment i work on a breadboard. just a atmege 328, cups and the poti.

the potis wiper is connected to A5.

i also use a 10k poti, but when i turn it to zero, it smokes :-)
is there a diff. between A0 and A5 ?
is there no high resistance in the A0-A5 ?

i connected the potis first pin direct to the +5V power that also
feeds the breadboard.

ARef (Pin 21) of Atmega328 is NOT connected to a cup. could
this be the problem ?

Grumpy_Mike

Quote
i also use a 10k pot, but when i turn it to zero, it smokes :-)

This means you have not wired it up correctly. You have the wiper either at 5V or ground.
Supply a photo and we can tell you which error you made.

GoForSmoke


i also use a 10k poti, but when i turn it to zero, it smokes :-)


That may be real bad news for the Arduino.
I find it harder to express logic in English than in Code.
Sometimes an example says more than many times as many words.

Frank Burns

i can upload a photo later.

but am i wrong ?
at a 10k poti the resistance on the wiper is between 0 and 10000 ohm ?

retrolefty

Quote
but am i wrong ?
at a 10k poti the resistance on the wiper is between 0 and 10000 ohm ?


You are correct. However if you miswired the pot into a circuit such that the wiper is wired to ground or +5vdc and one end or the other end of the pot is also wired to +5vdc or ground, then you can create a short circuit condition between the wiper and one end of the pot when the pot is turned to one extreme position. How you are wiring up the pot is the problem, not the pot itself.


Frank Burns

ok, i tested the poti in on a fresh breadboard and it works.
on the new breadboard the ARef is conn. to +5V. maybe
thats the different.
now i will test the poti in the complete circuit of the PCB
(this time with conn. ARef).

i will report if it DONT work. otherwise thanks for help :-)

Grumpy_Mike

Quote
on the new breadboard the ARef is conn. to +5V. maybe
thats the different.

No, you should not connect th ARef to anything.

Can't you face the fact that while you knew what to do correctly, when it came to actually doing it you got it wrong? That happens all the time in electronics to everyone, even me!

Frank Burns

ok, it works.....

the only thing i done is to connect ARef with +5V.

somewhere i read that without a connection to ARef
the Atmega uses a 1.1V Ref.Voltage.
Maybe this is why my poti smokes if i use it with 5V.


Grumpy_Mike

Ok let me say it again.
1) Don't connect ARef to anything, it is not needed and could potentially damage your arduino.
2) You smoked your pot because you wired it up wrong, plane and simple. The fact it works now is that you have it wired up right now.

Quote
somewhere i read that without a connection to ARef
the Atmega uses a 1.1V Ref.Voltage.

You either miss understood it or it was rubbish.

The value of the reference voltage has absolutely no affect on your pot. If you used a lower VRef and 5V on the pot all that would happen is that the maximum reading would be reached sooner in the rotation.

retrolefty

Quote
somewhere i read that without a connection to ARef
the Atmega uses a 1.1V Ref.Voltage.
Maybe this is why my poti smokes if i use it with 5V.


Your read wrong, or misunderstood what you read. For normal analogRead functions where you are reading a DC voltage between 0 and +5vdc applied to a analog input pin, you should have nothing wired to the Aref pin. Miswiring the Aref pin can also cause internal damage to the chip and should be used only when you fully understand the why and how of using external reference voltages for the arduino chip.


Lefty



Frank Burns

plz read my post nr. #4.

iam on a breadboard where ARef was not connected

AWOL

Quote
plz read my post nr. #4.

Post #4 was Grumpy Mike's.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

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