# Trimmer pots and resistance values

Discussion in 'Electronic Basics' started by max-man, Oct 29, 2005.

1. ### max-manGuest

I need to get hold of a 1.5K trimmer pot for an old arcade game
monitor but cannot find one of this value anywhere. Seeing as it's
essential that I use 1.5K but the closest that I can find is 1K or
2.5K, is there any way that I could modify, for example, a 1K pot with
a 0.5K resistor to give the correct value, or won't that work seeing
as it would be external to the pot and wiper?

2. ### John FieldsGuest

---
Depends.

If you need one end of the control to look like zero ohms and the
other end to look like 1.5k, and the pot is wired like a rheostat,
that's one requirement.

If it's wired like a voltage divider, that's another.

However, if all you need is a trimpot and all you can get is a
2.5kohm unit, and you need a rheostat, solder it in and trim it up
until it looks like 1.5K and you should be fine.

If not, post back and I'm sure at least one of us will be happy to

3. ### max-manGuest

Thanks. I should have said that all three pins of the pot are used so
I assume that makes the pot value even more critical?

4. ### ChrisGuest

Hi, Max. I kind of wish you'd have given some more information on the
circuit, and how your trimmer is being used.

Anyway, there are a number of things you can do. First, 2K is actually
very common for trimmers -- check the Digi-Key catalog. Since many
pots are rated at +/-20%, the high end of the tolerance might be close
enough. You might want to try it.

Another thing you can do if it's being used as a voltage divider is to
put a 5.6K 5% resistor across the legs of the pot. The total
leg-to-leg resistance will then be almost 1.5K, and the wiper will
scroll across the right voltage range.

.-----o
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.-. .-.
5.6K | | | |<--
| | | |
'-' '-'2K
| |
| |
'-----o
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

If you don't need the top 1/3 of the range, you might want to put a 510
ohm resistor in series with a 1K pot. This would have some value for
some applications.

o
|
.-.
510| |
| |
'-'
|
|
.-.
1K| |<--
| |
'-'
|
o
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

If you absolutely, positively have to have exactly 1.5K, and nothing
else will do, you might want to contact some manufacturers' reps, and
ask for a couple of samples. You'd be amazed at what a well-placed
request from a one-man engineering firm needing a sample for a
potentially good volume prototype can do.

Good luck
Chris

7. ### max-manGuest

<snip>

Excellent, many thanks.