Resistor and Capacitor Values

Hi John,

A lot of the values were selected based upon a lot of the early tube circuits.

AM radios and amplifiers were mostly standardized around a few designs for cost and performance.

Since there was a ready DIY market around the world, having a steady supply of kit parts helped manufacturers to decide what to produce.

In many ways, your basic low pass, band pass and high pass RC circuits remain unchanged from tube, transistor, to IC implementations.

So many of the old favorites are still useful today.

I am not sure how long the discrete components will still be available with all of the SMT and internal circuitry available on SOC designs.

I know I have a small stock of parts that I dip into all the time for projects.

DAB

There are good articles about this at Wikipedia: https://en.wikipedia.org/wiki/Resistor#Preferred_values  which links to https://en.wikipedia.org/wiki/Preferred_number#E_series

Each resistor has a tolerance like 10%, 5%, or 1%.  You want resistors that can cover all possible values, but since they vary there's not much point in having 10% resistors with values 1% apart.  So instead you cover a decade of resistors (e.g., 10 to 100 Ohms) with a minimal number of values that overlap each other when you consider the tolerance.  The values have a geometric progression, where each resistor is (for example) 10% larger than its predecessor.

For example, here are the familiar values for 10% resistors: 10 12 15 18 22 27 33 39 47 56 68 82 100

Hi DAB,

Thanks for your reply. I have lots of discrete components stored away so I will probably not run out but I too am concerned about the loss of discrete production to SMD. It is the new and interesting SMD components that will be harder to experiment with. If there is enough demand I bet there will be a company that takes the SMD and repackages it with an adapter so that experimenters like you and I can still work with them. I have already seen many little adapter boards that will turn an SMD into a more usable through the board mount.

John

This is in response to John Beetem

Hi John,

Thanks for the WIKI link. I read it and it all makes sense. It is strange how we take for granted the way things are without asking questions. I like to think that I do not do this but here I am an old guy asking a question I should have asked many years ago.

John

E14 just choked on my link to you !!!!

There is no reason not to use SM parts at home and it isn't hard to solder Rs and Cs down to 0603 using only a headband magnifier and a fine tipped iron. To do 0.5mm pitch QFPs you'll probably need a microscope.

You can use copper clad board to prototype on - scratch out gaps with a scalpel or Dremmel (or copy of one).

Google 'copper clad board rf' and look at the pictures - I did post some links but E14 dies when it tried to understand them.

if you hang out on sci.electronics.design and look for picture links posted by John Larkin you'll get some ideas of how to do this kind of prototyping. (Be warned - there is a lot of Off topic noise on sed !!)

MK

John Wiltrout wrote:

 

I have already seen many little adapter boards that will turn an SMD into a more usable through the board mount.

Schmartboard has a nice collection of these: http://schmartboard.com/index.asp?page=products

I agree with michaelkellett that some SMDs -- e.g., down to 0603 -- are pretty easy to work with.  In fact, I often prefer fixing a problem by adding a few friendly SMDs to a board with #30 wire instead of trying to find room for through-hole devices.

Hi Michael,

Thank you for your reply. I will check out the site. Sorry your posting got eaten by E-14.

John

Hi John,  The Schmartboard site is a keeper. This type of innovation is exactly why we will not have to worry about experimenting disappearing until the dimensions of the SMDs shrink out of sight.

John