How do I choose a potentiometer?

kelvinhall05 · December 23, 2018

Yes, I know. It's a noob question. But everyone starts somewhere, so I'd appreciate if someone could help me out. I mentioned in another post on this subforum that I'm building a simple little circuit to control a character LCD. I'd be using this by using SPDT switches to pull the 8 data lines on the LCD itself high or low, which would translate to binary which translates to ASCII, yata yata yata. I everything mostly figured out except for one big thing: I need a potentiometer to control the contrast of the screen. The problem is that I don't know which one to get. The only thing I know I want is for it to be a dial and for it to be panel mounted. I found these two on Digikey, and was wondering if these would work (I'm powering everything off 4 rechargeable AAs, so 4.8V total IIRC).

https://www.digikey.com/product-detail/en/tt-electronics-bi/P0915N-FC15BR10K/987-1649-ND/4780740

https://www.digikey.com/product-detail/en/bourns-inc/3310C-001-503L/3310C-001-503L-ND/1088212

If it helps anyone, here are the switches I'm planning on using, and here's the screen I'm gonna use:

Switches: https://www.digikey.com/product-detail/en/100SP1T2B3M2QEH/EG2361-ND/378830/?itemSeq=280312988

Screen: https://www.digikey.com/product-detail/en/NHD-0216K1Z-FL-YBW/NHD-0216K1Z-FL-YBW-ND/1701171/?itemSeq=280313021

One last thing: here is a schematic from 8bitguy's video series that inspired this idea named "How does a character LCD work?", as well as a pinout for the LCD:

Spoiler

Thank you!

r4tch3t · December 23, 2018

1 hour ago, kelvinhall05 said:

Yes, I know. It's a noob question. But everyone starts somewhere, so I'd appreciate if someone could help me out. I mentioned in another post on this subforum that I'm building a simple little circuit to control a character LCD. I'd be using this by using SPDT switches to pull the 8 data lines on the LCD itself high or low, which would translate to binary which translates to ASCII, yata yata yata. I everything mostly figured out except for one big thing: I need a potentiometer to control the contrast of the screen. The problem is that I don't know which one to get. The only thing I know I want is for it to be a dial and for it to be panel mounted. I found these two on Digikey, and was wondering if these would work (I'm powering everything off 4 rechargeable AAs, so 4.8V total IIRC).

https://www.digikey.com/product-detail/en/tt-electronics-bi/P0915N-FC15BR10K/987-1649-ND/4780740

https://www.digikey.com/product-detail/en/bourns-inc/3310C-001-503L/3310C-001-503L-ND/1088212

If it helps anyone, here are the switches I'm planning on using, and here's the screen I'm gonna use:

Switches: https://www.digikey.com/product-detail/en/100SP1T2B3M2QEH/EG2361-ND/378830/?itemSeq=280312988

Screen: https://www.digikey.com/product-detail/en/NHD-0216K1Z-FL-YBW/NHD-0216K1Z-FL-YBW-ND/1701171/?itemSeq=280313021

One last thing: here is a schematic from 8bitguy's video series that inspired this idea named "How does a character LCD work?", as well as a pinout for the LCD:

Hide contents

Thank you!

The first one you linked should work fine. You need a 10k potentiometer.

mariushm · December 24, 2018

A potentiometer is an adjustable resistor , you can think of it like two resistors in series, with the wiper (3rd pin) in the center :

0 ohm ------[ resistance ] ---(wiper)--- [ resistance ] ---- max ohm value

If you want to save space on the board, you can use a potentiometer to set the contrast initially, then take out the potentiometer and measure the two resistances and install two resistors of values very close to those you measured.

You can use any potentiometer, the differences between them are mostly how many turns you can do to reach the maximum value and whether it's a linear potentiometer (value increases linearly as you turn the knob) or if it's a logarithmic (a bit more expensive and used mostly for audio applications)

The datasheet for the display you linked to recommends a potentiometer with the values between 10-20 kOhm so you should probably be fine with a 10kOhm or a 25kOhm potentiometer. These are standard and popular values, so they're bound to be cheaper.

Above these values, 47kOhm and 50kOhm should be very common.

Of the ones you linked the style of the Bourns one (the blue 50k potentiometer) is the most user friendly imho.

Any of the ones in this pre-filtered list should work fine for your needs : https://www.digikey.com/short/pcb2nz

You probably also ignored or didn't notice the trimmer potentiometers : https://www.digikey.com/short/pcb22v

They're much cheaper and they'll work fine for this purpose, adjusting the contrast maybe a few times. They're not designed for constant use, but for this use case where you set the contrast a couple of times and then forget, they'll work great.

You can just solder wires to the pins if they're not spaced to fit directly on breadboard and you can use a regular screwdriver (though plastic tip is recommended) to adjust the value.