How do you clip the range of pot? I dont quite know the resistance I need yet but on a controller I want to clip the range so my motor cant go past a certain speed. By clipping the bottom end I limit the speed but dont want to go over 10k.
Is there a cheat sheet that if you attach to certain posts this happens? I assume adding a 5k resistor in line will yield a 5k-15k pot so not quite what I want.
Thanks,
Presumably there is an Arduino is the mix somewhere?
Why don't you use analogRead() to get the potentiometer (voltage) value, and use that in your code to determine how fast to drive the motor?
5e simplest way to do this is to add a resistor between one end of the pot and where that end would normally go.
If it restricts in the wrong direction, then change the end of the pot you use.
it would help to understand what it is exactly that you are trying to achieve?
From you post we can probably assume you already have a 10k pot?
You said if you add 5k in (presumably in series) then this would result in a total resistance of 15k which is NOT what you want. I am guessing therefore that you want to achieve something like a 7k/3k split? Or maybe something else?
If you decide to use your 10k pot and with analogread() as red_car suggests, then you can also use map() to map the range of returned values to a range of your choice, but again, I am only guessing here as t what is required and in what way the Arduino might be involved.
Perhaps you could share your sketch and a diagram of what you are trying to accomplish?
If I understand correctly, you simply want to map the potentiometer values (0-1023) to your motor speeds. Look into the 'map' function, which might be exactly what you're looking for. To cap the top speed, just change the high-end of the mapped speed value.
Why not?
While a pot being read by an analogue input ideally should be 10K, a 15K pot will work just as well. I use 22K pots because they were cheaper when it came to buying a batch, and they are every bit as responsive as 10K pots.
It is only when using pots with a total resistance of 100K or greater that you can get a problem if you want to use them to quickly scan a number of them.
I would agree with patduino and just map your analog in from a pot to whatever you want your motor to do using PWM.
Next using your given numbers of 15K and 5K If you place the 5K to ground and we assume 5.0 volts applied the Rtotal is 20K so 5 Volts / 20K = 250 uA for the current. The 5K will drop 1.25 Volts off the bottom so the pot wiper out will vary between 3.750 volts and 5.00 volts. Move the 5K to the top of the divider and you get 0 volts to 3.75 volts.
Personally I would just use a single 10 K potentiometer giving you 0 to 5.0 volts analog in which will be 0 to 1023 bits and map the analog in to what you want between 0 and 255. Also as Grumpy Mike points out you can use a higher value than 10K and it will work fine just using 10K here as an example. I would also use a 10K 10 Turn pot simply for better control.
No cheat sheet, you just apply the basic math. Bottom line in your example of 5K and 15K it's a matter of where the fixed resistance verse the variable resistance (the pot) is in the circuit.
Also my bad I see what you mean as to adding 5K and 10K getting 15 K but really matters not. With Rtotal = 15K just do the math 5 Volts / 15000 Ohms = 333 uA so the 5K would drop 1.666 Volts. Just do the math and again I would just use a 10K ten turn pot to your analog in and map it. I am also assuming an Arduino Uno so 5.0 Volts?
Ron
If you put a 10k fixed resistor in parallel with your 10k pot, you should get something that behaves like a 5k pot. Connect that in series with a 5k pot, and the circuit should give you 5k to 10k.
(I'm not sure, offhand, whether the linearity would change.)
Ok, im struggling to quote in mobile.
So I am not planning on using an Arduino in the project.
I am using a cytron 30A dc motor driver which has a spot for a Pot that would basically control speed. Im guessing its just doing a voltage divider as a signal to control the pwm.
Im looking to do this analog with just resistors across the potentiometer.
So the current range of the pot is 0-10k. I want to clip the bottom end so it becomes 2.5k-10k or 5k-10k range. That way the speed can be adjusted but it doesnt go super fast. Im trying to limit the end user from going to fast.
I could easily do it with an arduino but dont want to have to use one if I dont have too since there is a pot available to it and its battery powered so I dont want to add any more current draw no matter how small.
Im just trying to figure out a resistor attached to which posts does what to the pot. I can just do it on a bench and figure it out when it arrives but wanted to have it sorted before it showed up?
Hopefully this paints a clearer picture.
Thanks
A 2.2k resistor between Vcc and one end of pot (the other end grounded) would make the pot voltage 0 to 82% of Vcc.
I think what you really want to to clip the voltage that is seen at the analog pin that controls the onboard PWM generator.
Your pot is essentially connected like this...
and the voltage at Vout is given by...
Vout= (Vin x R2) / (R1 + R2)
So... if you add a resistor (as @JCA34F suggested), you are effectively increasing R1, which will then reduce the voltage at Vout. This will reduce the top speed of the motor.
This is a lot easier to do if you use an external pot for the driver rather than the one on the PCB.
Hi,
Try this circuit;
Use the two trip pots to set your min and max speeds.
The trimpots may interact with each other so you may have you repeat adjustments to get your range setup.
The 2K value is arbitrary, you may have to change them if you cannot get the range you want.
Not sure what your supply voltage is, assumed 5V, but even higher voltage should not be a problem.
This is how some industrial, out of the box DC/AC Universal small motor controllers provide the user with preset speed limits.
Tom.. 
What is the voltage across the pot? What is the maximum voltage you want from the pot?
This is the user manual for your motor controller. I would use the schematic suggested by Tom George in post #12 above. That gives you a low end and high end trim. If you don't want or need low end trim just omit the low side pot. I would still run with a 10 turn pot for the main control.
Ron
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