EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Hextejas on February 13, 2018, 06:09:26 pm
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I have a cheap function generator with a PCB. There is a YouTube review and suggestions as to how to fix it.
One of the suggestions is to wire 2 of the pots in parallel. I have no clue how to do that. My 1st guess was to wire them together pin to pin. But that seems wrong somehow plus what do I wire into the PCB in place of the 2 pots ?
Maybe after wiring them together, put them back into where they came from.
The resultant impact on the rest of the circuit is beyond me.
I cannot see how to do this.
Thanks
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You haven't given us enough context to guess. We don't even know what the problem you want to fix is.
Perhaps you should ask the person who made the suggestion what they meant?
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You haven't given us enough context to guess. We don't even know what the problem you want to fix is.
Perhaps you should ask the person who made the suggestion what they meant?
Well, let me see if I can make it clearer. The pots are very simple like these.
So, I have 2 of them to be wired in paralle. Resistors and capacitors i can do, but these are a puzzle.l
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Do you understand what a pot is first of all?
Basically it is effectively 2 resistors that add up to the total value with the cut off point adjustable so all the way clockwise might be (assuming a 10K pot) 0 between the right pin and the centre and 10K between the left pin and the centre. As you turn the pot anti clockwise the value of the resistance between the right pin and the centre goes up whilst the other goes down but they always add up to the total ie 1K and 9K, 2K and 8K, 3K and 7K, 5K and 5K....10K and 0
With that explained leaving the original pot in and adding a second pot is just like adding two more resistors. So with pot1 all the way clockwise and pot2 all the way clockwise it is like having two 0ohm resistors in parallel between the right and centre with 2 10K resistors (parallel) between the left and centre. As you turn each pot you will get different results so turning one all the way in the other direction would give 0 and 10K in parallel for both pairs.
I'm not sure why you would want to do that without seeing the problem and solution but that explains it. How you do it matters not so long as the centre pins match up. Having them mirroring each other will mean that you would turn the added pot in the opposite direction. Having them matching pin for pin would be harder to fit BUT they would turn in the same direction.
HOWEVER
I would suggest that what you need to do is remove the original pot and fit ONE new pot of a different value and fitting two in parallel is just going to cause it to be difficult to adjust to a relevant value. This is why we need to know what is going on.
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Do you understand what a pot is first of all?
A pot is short for potentiometer which is a variable resistor.
My 1st shot at it and when I did it on a breadboard I got the correct ohms as calculated.
And schematic.
The 2 pots are 100k and 1meg.
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Now we have the actual circuit basically the dual pots now make sense. Just wire them pin to pin and set the fine control one in the middle then adjust the rough control one to about right. At that point you can fine tune with the fine one......
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That is kind of a weird scheme. The 1M "fine" control will have a small influence when it is at the high resistance end of its range, but at the low resistance end of the range it will totally swamp the "coarse" control!
A better way to to get coarse/fine is to use series connected pots.
Still wire up the 100K coarse just like it is.
Get rid of the 1M pot.
Wire up a smaller 10K pot as your new "fine" control in series, in between the fixed 5.1K resistor and the 100K pot.
You can still use the 10K as a 2 terminal device, by wiring the center "wiper" pin to the upper pin.
The total resistance range will now go from 0 to 110K, with at most 10K coming from the fine control
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That is kind of a weird scheme. The 1M "fine" control will have a small influence when it is at the high resistance end of its range, but at the low resistance end of the range it will totally swamp the "coarse" control!
A better way to to get coarse/fine is to use series connected pots.
I agree with using them in series :) This is how I would actually do it if I were designing the circuit from scratch. If the coarse only needs setting once and the fine is a big enough sweep then you could use a cheaper board mounted preset pot for the coarse instead.
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Do you understand what a pot is first of all?
A pot is short for potentiometer which is a variable resistor.
My 1st shot at it and when I did it on a breadboard I got the correct ohms as calculated.
And schematic.
The 2 pots are 100k and 1meg.
A pot is short for potentiometer.... but simply viewing it as a "variable resistor" is oversimplification. After all, a "variable resistor" only needs two terminals, not three. The potentiometer is a "potential" (meaning voltage) "meter" (meaning a regulation or setting device.) As typically used, there is a voltage across the entire unit (between the fixed terminals) and the tap makes this into a voltage divider: Two resistors in series, with a tap at the connection point -- an adjustable voltage divider.
But of course the same device can also be used as a mere 2-terminal variable resistor, by tying the tap to one of the end terminals. As I see they are being used in the schematic.
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Curious, but that is the original design. 100k course, 10k fine, in series. The reviewer didn't like it and came up with this config. I will try and find it. It was on facebook.
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Anyone can fiddle with a circuit - but it takes a bit more skill to actually design one.
I'd be curious about the reviewer's reasons for not liking the original design.
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Anyone can fiddle with a circuit - but it takes a bit more skill to actually design one.
I'd be curious about the reviewer's reasons for not liking the original design.
OK. Let me find a link to his video. I think that the dude is pretty highly regarded.
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Found it. Kankai Labs.
[urll]https://www.youtube.com/watchv=f_gnoU22Dj0&sns=em[/url]
Its about 45 minutes and the dude sounds like he knows what's what.