# Robin Barton

### General

Beaufort Wind Scale
Convert Units
IP Rating

### Electronics

Basic Calculations
Resistor Calculator
Resistor Circuits
Resistor Colour Code

### Mechanical

Centre of Gravity
Centre of Mass

# Resistor Circuits

Resistors are commonly combined in one of the following configurations: Series, Parallel or Bridge. These circuits are discussed below.

## Series Resistors

If the resistors are connected in series, the total resistance is equal to the sum of the individual resistances i.e.:

RTotal = R1 + R2 + ... + Rn

 Example: Three resistors are connected in series.They have values of: 1kΩ, 2kΩ and 3kΩ.RTotal = 1kΩ + 2kΩ + 3kΩ = 6kΩ

Series resistors are often used as voltage dividers to provide a reference voltage of a fixed percentage of the supply voltage. Below is an interactive example.

⚠ The application of these circuits requires careful consideration as the load can affect the effective resistance of the part of the divider that it is connected across - see parallel resistors.

 Resistance: m kM Ω m kM Ω RTotal: Circuit: Ⓐ— R1 ———┬——— R2 —Ⓑ Current: Ⓧ Voltage: ⬑ VR1 ⬏ ⬑ VR2 ⬏ VⒶ VⓍ VⒷ

## Parallel Resistors

If resistors are connected in parallel, the total resistance is equal to the inverse of the sum of the inverse of the individual resistances i.e.:

⅟RTotal = ⅟R1 + ⅟R2 + ... + ⅟Rn

 Example: Three resistors are connected in parallel.They have values of: 1kΩ, 2kΩ and 3kΩ.⅟ RTotal = ⅟1kΩ + ⅟2kΩ + ⅟3kΩ = 545.455Ω ☀Handy Hint: The result will always be less than the lowest resistor value.

Parallel resistors are often used to obtain non-preffered resistance values i.e. where a value is required that cannot be bought off the shelf or as current dividers (shunts). Parallel resistance calculations also come into play when you introduce a load across part of a voltage divider. Below is an interactive example.

 m kM Ω ╭ — R1 — ╮ Circuit: Ⓐ— ┤ ├ —Ⓑ ╰ — R2 — ╯ m kM Ω Is equivalent to: Circuit: Ⓐ— Ω —Ⓑ

## Resistor Bridge

Resistor Bridges are generally used for measurement circuits for example Wheatstone Bridge circuits. Normally one of the resistors would be replaced with a device such as a thermistor or light dependant resistor. They combine series and parallel resistances.

 VⓍ: V m kM Ω Ⓧ m kM Ω ╭ — R1 — ┴ — R2 — ╮ VⒶ: │ VXY V │ VⒷ: Ⓐ— ┤ ├ —Ⓑ │ │ ╰ — R3 — ┬ — R4 — ╯ m kM Ω Ⓨ m kM Ω VⓎ: V