Online calculators have proliferated. Consider that one site dubbed omnicalculator.com now hosts over 1,800 online calculators in various disciplines. But when it comes to electronics and engineering, the pickings are slimmer. Calculatoredge.com provides numerous online calculators for engineers of which a little over 100 are in electronics and electrical engineering.

That brings us to Digi-Key which has assembled a set of electronics converters and calculators that aim to accelerate workflow in the lab or shop. Hosted on the Digi-Key site are highly instructive conversion and calculation tools, each with a quick tutorial. Some are simple, one-step operations, while others are more complex. Here are few highlights:

*Battery-life calculator*: The battery-life calculator depends upon one simple algebraic formula: Battery life = (battery capacity in mAh/load current in mAh). This calculator is handy if, in the first stage of designing a mobile device, you must choose a battery and allocate space for it.

*Capacitance conversion*: This tool converts capacitance values into units of picofarad, nanofarad, microfarad and Farad. An accompanying chart lets you find the capacitance by looking up the capacitor code: The first two digits are the value in picofarads, while the third is the multiplier. If no multiplier is given, the result is capacitance in pF.

*Capacitor safety discharge calculator*: The tool is used for calculations involving the discharge of a capacitor through a fixed resistance. Given a capacitance value as well as beginning and end voltages, this calculator solves for either time or resistance, calculating the resulting initial power dissipation in the resistance and the total energy to zero volts.

*Current-divider calculator*: This tool calculates the current flow through each of up to ten parallel resistances connected to a power source. The formula is I_{n} (the current through resistor R_{n}) = I_{s} (R_{total} /R_{n}) where R_{total} = The total equivalent parallel resistance of the resistor array across the current source and I_{s }is the current from the source.

*dBm to watts conversion*: To operate this converter, the user fills in either the decibel-milliwatt field or the watt field. The power conversion formula for dBm to watts is: P(w) – 1 w × 10^{P(dBm)/10}/1,000 = 10^{(P(dBm) – 30)/10} .

*Decimal fraction conversion*: This tool converts decimal values to their equivalent fractional values. The resulting fractions use the closest value based on the denominator selected. A related graphic with a slider locates the fractional result when a decimal is entered.

*Energy conversion*: The fields that can be populated are British thermal units, Joules, kilowatt hours, therms, calories (nutritional) and calories (thermochemical). For example, enter one Joule and you are instantly informed about the amount of energy in each of the above measurements. A Joule, for example, is equal to 0.2390057361 thermochemical calories, each of which is about a thousand times larger than a nutritional calorie.

*Force conversion*: Fields are newtons, gram-force, metric ton-force, short ton-force, sthene (if you’re wondering, this is an obsolete unit of force or thrust in the meter–ton–second system of units introduced in France in 1919), pound-force, dyne, poundal and long ton-force (UK). Relevant formulas are: 0ne newton = one Joule/meter. One newton = one kilogram meter/second squared. A newton, accordingly, is a function of space, time and mass.

*Inductance conversion* has these fields, which can be populated, any one of which translates into the other fields: Picohenry, nanohenry, microhenry, millihenry, henry and kilohenry. A chart is provided showing the inductances.

*LED series resistor* calculator: This tool is used to calculate the resistance needed to drive one or more series-connected LEDs from a voltage source at a specified current level. The calculator advises that the user choose a resistor having a power rating about two to ten times the calculated value to avoid excessive temperature rise. The relevant formula is R = (V_{s} – V_{f})/I_{f }where V_{f} and I_{f} are the forward voltage drop and forward current of the LED. Typical V_{f} ranges for LEDs are: Red, 1.8 to 2.1; Amber, 2 to 2.2; Orange, 1.9 to 2.2; Yellow, 1.9 to 2.2; Green, 2 to 3.1; Blue, 3 to 3.7; and White, 3 to 3.4.

*Length conversion*: The input ranges from fractions of one micron to kilometers, yards, feet and inches. The generic conversion equation is one cm = 0.393701 in.

*PCB trace width calculator*: This calculation can be critical because trace width equates to ampacity. An undersized trace becomes an overloaded fuse. Too wide possibly means less separation between opposite-polarity lines and possible solder bridges. To use the calculator, you need to know current, trace thickness, temperature rise, ambient temperature and trace length.

The* time constant calculator* computes the product of resistance and capacitance values, i.e. the RC time constant, the time needed for the voltage present across the capacitor to reach approximately 63.2% of its final value after a change in voltage is applied. The total energy stored in a capacitor charged to a specified voltage is also calculated. The inputs are voltage, capacitance and load resistance. The outputs are time constants and energy. The relevant formulas are: E = (V^{2}× C)/2 and τ = RC.

*Wire size conversion calculator*: Used to calculate the nominal equivalent values of wire sizes such as American Wire Gauge (AWG), square millimeter area, circular mil area and more. Just put in a known measurement or value and all of the equivalent sizes are automatically calculated and displayed. The conversions are all based on solid wire. The American Wire Gauge, also known as the Brown and Sharpe Wire Gauge, was developed in 1855. The measurement originated by counting the number of times the wire needed to be drawn through a die to reach the desired size. Because of this, the sizes are inversely and logarithmically proportional, meaning larger wires have a smaller AWG number. A 10 AWG wire has approximately ten times more area than a 20 AWG wire. AWG is commonly used in North America and over 65 other countries.

*Frequency to wavelength conversion*: The ITU radio frequency-to-wavelength converter lets you to enter a frequency from 8.3 kHz to 11.2 GHz and calculate the wavelength. It also demonstrates the primary ITU allocation for the frequency.

*555 timer calculator*: The 555 timer is a commonly used IC that can be configured to produce a square-wave output. In astable configuration, this output is a free-running square-wave. In monostable mode, the output is a single high pulse generated for a single input event. This calculator will determine the pulse width if the output based on the resistance and capacitance values are entered.

*Tee attenuator calculator*: The Tee attenuator calculator will calculate the values of R_{1} and R_{2}. Enter the required attenuation and the impedance of the line to be matched.

*Bridge Tee attenuator calculator*: A bridge tee attenuator is a modified pi topology attenuator. It permits you to attenuate the signal without changing the system impedance. Enter attenuation (db) and impedance. R_{1} and R_{2} are displayed.

*Reflection attenuation calculator*: A reflection attenuator uses two equal resistors grounded and tied to the same node to attenuate a signal. There are two possible outputs depending on whether or not the resistance is higher than the system impedance. This calculator allows the user to find two possible resistor values for the attenuator. Attenuation (dB) and impedance are the fields to be populated. The outputs are R_{1} > Z0 and R_{1} < Z0.

*Pi attenuator calculator*: The pi attenuator uses a series resistor and two shunts to ground to attenuate a signal. This calculator allows you to enter the desired attenuation in dB and the system impedance. It calculates the required shunt resistor and series resistor.

*SMD resistor code*: The surface-mount resistor code calculator uses the markings found on the device. Choose the code format: three-digit EIA, or four-digit EIA, or EIA-96. Standard tolerance SMD resistors use a three-digit code to mark the resistance. The first two numbers indicate the significant digits and the third is the multiplier. R is used to indicate the position of the decimal point.

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