Device to act as 0 - 9V source

barry said:

That's not a great picture, but it sure looks like you've got the battery connected to the wiper.

See post #11.

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No, like the guy below said, the markings on the red board is right, the positioning of the pins dont match with the positioning of the tabs on the pot itself.

ads-ee said:

The labels on the "pins" that are on the red circuit board are labeled S + - so if those are correct it's hooked up to the battery correctly.

I'd disconnect the potentiometer and check using the "tabs" at the top of the potentiometer and measure the resistance across the outer pair with a multimeter.

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Youre right. I have now tested the pot and measured the ohms, and i got 10k from each end of the pot, and the wiper seemed to work like it should, from 0-10k ohms when turning it, with 5k at the middle.

barry said:

What did you mean when you said the voltmeter range is 2.5-30V? Can it measure below 2.5V? And have you tried using a DVM to verify the readings from your little meter?

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It can measure below 2,5V but its only a 2 wire voltmeter, so the voltage measured is also the voltage powering the voltmeter. Could this be the problem? When measuring it the intrument barley moved, so i would guess 50kohm>.
I am currently working on modifying it so that i can supply the voltmeter power from a seperate wire.

Audioguru said:

It is obvious that the pot is a logarithmic volume control, not a linear pot.
Without a load when it is turned to half then its output voltage is 0.45V to 0.9V. If it is turned down 20% then its output voltage might be 2.5V.

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Im not sure that i get you right, but i got 5kohms in the middle position and 10k ohms to the far side.

Venkadesh_M said:

not only a logarithmic pot but also in linear pot if the potentiometer resistance is high and if the load resistance is low the same non linearity will arise ..... try a pot with lower resistance if your source doesn't support try a voltage regulator (output voltage controllable), if you still thought it was inefficient you can use a switched regulator (If you want linearity)..
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In all the images the pot is in center position according to the load the output voltage varies.....
For better operation the Potentiometer resistance shd be lower than load resistance.....

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I have yet to find an easily controllable voltage regulator.
I will look into the switching regulator.

shatruddha said:

Hi barry!!
sorry to misread you, I was thinking something else.

BTW for Pot based circuit, I think your device will turn up more into a device dependent voltage as well, since your device impedance will matter a lot when you are setting a voltage.
I would still go on with a buck converter, making one is pretty easy, you can just google it and you'll find some really easy solutions. You just need a capacitor, inductor, a mosfet and a comparator. And of-course a pwm signal

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The buck converter sounds awfully complicated to build and hard to control when i just want a 0-10v output.
How will a transistor work ?

Many digital voltmeters cannot measure the voltage that powers them.
Your voltmeter obviously does not have enough voltage to power it when the voltage is 2.5V or less.

Now that you measured the ohms of your pot then it is linear, not logarithmic.

when you taking the power from measuring end It takes a lot power from the source so that also loads the potentiometer, It takes the current for All LEDs in the meter... so it should be connected separately and it can take 10 uA in the measuring probe......

I think I would try powering the meter directly from the battery.
Use the pot across the battery as you have and add a rail to rail opamp wired as a non-inverting buffer.
The opamp would be powered from the battery (same as meter) and the +in terminal will go direct to the wiper.
The -in is wired directly to opamp output for 100% feedback.
Depending on the opamp this will allow 20mA or more o/p drive.

This will provide near zero to near Vbatt as your output not 0 to 10V as per the post title.

Heres an update for you who is still curious about this
Its been a while scince ive done anyting with it, but lately ive managed to salvage a LM317 voltage regualtor from an old VFD. Couldnt be bothered to order something online with a month shipping time...
I made a little circuit and it does its job well enough for me to use it. Range is from ~0,9V (0V if you turn it off of course) to ~8,9V.
**broken link removed** **broken link removed**
Ive done some modifications to make it work properly. First i poked around the voltmeter and found a spot to connect another wire so i coud push constant voltage from the battery to power it, now its as bright as the sun
**broken link removed**
Note: Ive separated the new wire from the old circuit by cutting it off at the edge of the white plug.
As some of the voltage drops over the LM317 ive gone over to a smaller 12V battery (23A).
The circuit:
**broken link removed**
I have yet to find a nice box to put it in.
Ive added 2 wires(red twisted pair) for battery test, however this measures only 10V even though the batt is 12V, my guess would be that there is some loss somewhere while the circuit is live. A pushbutton is going on these wires when put in a box.
Else the voltmeter is suprisingly accurate.
Note: Be careful when soldering on this type of switch as i use for my power switch for the circuit. IF it gets too hot it will melt and come loose inside.

Closeup of the circuit board:
**broken link removed**
I could make it one "hole" smaller in each direction but i want to have room for expansion.
Not the prettiest but i like it

The tiny 12V battery is very overloaded and will be dead very soon. A new one will be the same.