Variable resistor

I'm starting with electronics and I don't have a lot of resistors. Every new project I try to do, I have to buy new resistors, but they take a long time to arrive.

What's the solution? What variable resistors should I buy?

Thanks

• Why not just get one of those multi-packs of common values? – JustJeff Oct 10 '10 at 13:53

There is a thing named resistance decade. It is like a programmable resistor, you can set the value and it precisely holds it. Costs about 100 to 1000 USD depending on precision and wattage.

Other cheaper solution is to buy a Resistor Assortment Kit. It includes 20-50 pcs of every value of resistors. You can find it on ebay from 10 USD

• but it simulates just 1 resistor... i need an good solution that can 'simulate' like 5 resistors... – Andrew Oct 10 '10 at 15:03
• Yes. It is used to test/tune a circuit by finding the correct value for one resistor. If you need more, then the assortment kit is the solution. There is one more thing, the potentiometer. This is the variable resistor used in analog controls like volume. If you buy 5 pieces of 1K, 10K, 100K, 1M values, you will have more than enough variable resistors :) – csadam Oct 10 '10 at 15:10
• any link from some variable resistor kit in ebay? // thanks for your help – Andrew Oct 10 '10 at 15:32
• I've found only this assortment: cgi.ebay.com/… But it is US only. Anyways there are 5 pcs packs in each values if you search to "5pcs 1K potentiometer" then 10K, etc. And make sure to get linear ones, not the logarithmic type. – csadam Oct 10 '10 at 17:04

Another idea is to just buy resistors.

I buy resistors in packs of 100 for about 50p each; packs of 1,000 are also available for £2.88 each. They are 1/4W, 5%, carbon film.

First, I'd recommend you stock up on the most common values: 10, 47, 100, 470, 1k, 4.7k, 10k, 47k and 100k provide a good range. Then get the in-between values. You'll rarely find a use for 1M+ resistors, so I don't have any of them.

• There's too much of a gap between 10 and 47, 100 and 470 etc for my taste - I like to have no more than a factor of two jump. So add in 22, 220, 2.2k, etc. ohms. – DarenW Oct 19 '10 at 3:03
• @DarenW, I like your power-of-2 approach, but I've been thinking about going the opposite direction -- limiting the unique resistor values in my "carry with me everywhere" box to only power-of-10: 10, 100, 1K, 10K, 100K, 1M -- with at least a dozen of each. As Joby Taffey mentioned, we both can still form any possible resistor value to almost any desired precision with parallel and series combination. I don't know if the advantages of having 1/3 as many resistor bins in my box will outweigh the disadvantage of occasionally using 3 or 4 resistors in a location where you would only need 1 or 2. – davidcary May 2 '11 at 2:13

I would recommend getting an assortment of some kind from your electronics dealer, they should have some. You'll probably get them cheaper that way, too. If you do SMD, you might need separate sets for different sizes plus a pth kit. But the price still isn't bad and usually those kits are so big you won't have to worry about it after you buy one set. If you find yourself running out of one size (220Ω, 10kΩ), you can get a strip/tape of 100(0) and be set for a long while again.

In many cases you can get away with rounding the values a lot, so you'll probably only need a few per magnitude. You can combine values and a few pots/trimmers can help test values quickly (while prototyping).

That decade box (or such) can be made if you can find the switches. There should be ready schematics for various types.

Either way, I'd say stock up on a wide set of values. If you're doing anything more than putting together a ready kit now and then, you can probably use the selection. There's also a couple of other questions here about how to keep those parts in order, what parts to keep in stock, and what belongs into a "basic electronics kit".

One option is to combine resistors in series and parallel to produce the resistance you need.

Sometimes you can use a good emulator like qucs, that is free.

• Yeah, someday, when QUCS has a "print reality" button to click and out pops the physical part you just drew! – DarenW Oct 19 '10 at 3:00

you can buy a number of resistors at one time as there is a set of standard values for resistors.