by circuits.dk:

The first approximation is based on a modification of an expression developed by Wheeler; the second is derived from electromagnetic principles by approximating the sides of the spirals as current-sheets; and the third is a monomial expression derived from fitting to a large database of inductors (and the exact inductance values).

**Single layer Planar spiral coil inductor calculator –** [Link]

tanishqjain340 wrote this instructable detailing the build of his analog calculator project:

Do simple calculations with your math box.

The next time you need to crunch a couple of numbers, resist the urge to grab a digital calculator. Instead, round up some variable resistors, also known as potentiometers, and wire them into an analog mathematics rig. By twisting the potentiometers’ knobs and measuring the resulting voltage or resistance with a digital multimeter, you can perform simple multiplication and addition without a microprocessor in sight.

[via]

**Go analog with a resistance-based calculator –** [Link]

desmith.net hosts a nice little script to generate socket footprints for various CAD packages:

This program lets you determine the pin circle diameter of a tube base from measurements more readily made with a micrometer. The data should be entered in millimetres and the results will be in the same units. Script output for a package definition of the resulting socket can be generated for several CAD packages. Create a disk file from the output script and execute it in the relevant package – for Eagle execute the script as a SCR from the library editor.

**Valve & Nixie Socket Calculator –** [Link]

PCB design toolkit – PCB Via Current | PCB Trace Width | Differential Pair Calculator | PCB Impedance – [via]

The Saturn PCB Toolkit is the best resource for PCB related calculations you can find. It incorporates many features that PCB designers and engineers are in regular need of like current capacity of a PCB trace, via current, differential pairs and much more. Please download our PCB Toolkit today for free and enjoy!

**PCB design toolkit – PCB Via Current | PCB Trace Width | Differential Pair Calculator | PCB Impedance –** [Link]

Electro-Calc is a free software developed to facilitate the design of electronic and electrical projects. Unfortunately is not in English.

**Eletro-Calc Calculator v4 –** [Link]

**Amitor 1.1 – toroidal core coils Calculator**

The identification for the Amidon toroids consists of one or two letters (T=toroid and FT=ferrite toroid), followed by a number (for ex. T50), which represents the outer diameter dimension expressed in 0,1 inches, followed by a separation mark (dash, dot, stroke), followed by another number indicating the frequency mixture and the frequency range at which it would be recommended to use the toroid.

It should be taken in account that a toroid with a X declared frequency will be able to operate with fairly good performances even at 10 times higher frequencies and only the A factor will decrease.

The iron powder toroids are colored according to their mixture; the first color covers three sides and the second color the remaining side.

**Bobcalc 2.0 – Simple air Coil Calculator**

Simple software to calculate the air core coils, the most widely used in RF circuits and may use the software to determine the data to build a coil, knowing that the inductance of this coil. The software will give the result of how many turns will be required to achieve certain inductance value, and provides the wire diameter … In addition has a table with wires AWG mm thick.

**Toroidal Coil + Simple Air Coil Calculator –** [Link1]+ [Link2]

electronicsblog.net writes:

This is the very first and I hope not the last post of this blog. With this event I want to share with you LED calculator. It is also my first project with Visual C++ Expression 2008, this software development environment is free for students.

Calculator is capable of finding suitable standard E12 (10%) resistor value and power for one LED designs. There also some tips for user to find LED forward voltage:

**LED resistor calculator for windows –** [Link]

a resistor divider calculator spreadsheet [via]

Don’t we all have had frustrations galore when we were trying to fine tune the resistor divider for our voltage feedback on PS and LODs? Well, my good friend Art Nace came up with this wonderful tool to calculate the best fit values for the resistors for dividers. It even lets you specify voltage tolerances over temp. give it a try and let me know what you think?

**Resistor divider calculator –** [Link]

Neat small unit converter for electronic engineers. If you found this useful, but lack of features, please be free and report/ask for updates. This tool is completely free.

**DBCalc – dB Calculator freeware –** [Link]

Using this tool you can find closest simple resistors net of standard resistors values. Select net, select required resistance and you will got pair (or triplet) of resistors with combined value closest to your needs.

**EqResistors 2.0 – Resistors Combination Calculator –** [Link]