RMCybernetics - Electronics - Building Circuits

This page should help you learn about how different components can be combined to create useful circuits. We've included a range of example circuit diagrams and explanations of how they work. The circuits start from the very basics and move on to more advanced practical circuits.

Connecting Resistors Together

Resistors are commonly used for limiting the current available to part of a circuit, but they are also used together in networks to allow voltages to be distributed how you want it around a circuit.

Resistors in Series
Connecting resistors together in series allows you to increase the overall resistance of the chain. The values of each resistor can simply be added together to get the overall total value of resistance.

Resistors in Parallel
When resistors are connected in parallel the overall resistance is reduced. This is because there are more paths for the current to follow making it easier than just flowing through one device. Connecting two resistors in parallel that are of the same value simply halves the total resistance, connecting four in parallel makes the total resistance 1/4 of a single resistor, and so on.

When connecting resistors in parallel of different values the following formula is used. 1/R_T = 1/R₁ + 1/R₂ + 1/R₃

Voltage Dividers
A common use of resistors is to put them together to form a voltage divider. The term voltage divider (aka potential divider) is quite self descriptive as they are used to divide up the voltage into portions determined by the resistor values.

This diagram shows a simple example using a single battery and two resistors. The three points (A,B,C) on the circuit are where the voltage measurements can be made.

If this battery is 10V then the voltage between 'C' and 'A' will also be 10V. The voltage at 'B' is determined by the ratio of the values of the resistors R1 and R2. For example; if R1 and R2 are of the same value then the voltage at 'B' will be exactly half the voltage between 'A' and 'C'. The polarity of 'B' can be considered as either positive or negative depending upon whether you use 'A' or 'C' as reference for the measurement.

From this simple example you can have a three rail power supply with outputs of either 10V, 5V, 0V, or 5V, 0V, -5V with respect to A,B,C.

To get different voltage ratios you just alter the resistance ratio. For example; if R1 is 1k Ohms, and R2 is 9k Ohms, the voltage between 'C' and 'B' will be 1V, while the remaining 9V can be measured between 'B' and 'A'.

Connecting Capacitors Together

Capacitors are used as temporary energy storage devices and are often used for generating or tuning signals. Capacitors can also be connected up to work in the same way as as the voltage divider described above. The formulae used for capacitor networks are similar to those used for resistors but they are used in reverse with respect to series and parallel configurations.

Capacitors in Series
Connecting capacitors in series divides the voltage between each capacitor in a similar way to how it works for resistors. This is useful for creating high voltage capacitors from a series of lower rated ones. This technique is often used for making DIY homemade high voltage capacitors (known as an MMC) for use with devices like Tesla Coils. When capacitors are connected in series the total capacitance (C Total) is reduced. If two identical capacitors are connected in series the overall capacitance is half the value of a single one. This is usually expressed using the formula below.

When making a high voltage capacitor like an MMC, it is common to create several series strings of capacitors to match the desired voltage rating, and then to connect these in parallel.

Capacitors in Parallel
Capacitors are often connected in parallel to create a larger overall effective capacitance. The voltage tolerance remains the same while the capacitance of the capacitors can be added together to get the total. This is usually expressed using the formula;

RC Circuits (Resistors & Capacitors)

An RC circuit is simply some combination of a resistor and a capacitor. The value of the resistor in a circuit with a capacitor will change the rate at which the capacitor can be charged and discharged. This relationship is known as the RC time constant. The combination of resistors and capacitors can be very useful for timing circuits and also filtering signals.

Here a capacitor is placed in series with a resistor and an LED. The LED is simply used to give a visual indication to what is happening in the circuit. When the battery is first connected the capacitor will begin to charge and therefore a current will flow around the circuit. As the capacitor charges the current flow will decrease until the voltage across the capacitor is equal to the battery voltage. While C1 is charging you will see the LED light up and gradually fade out when C1 is fully charged. Releasing the switch will not reset the circuit. The capacitor must be discharged before the process can start again

This circuit is the same as before except the LED is placed in parralel with the capacitor. The LED will now light when the capacitor is charged. When SW1 is pressed there will be a small time delay before the LED gradually lights up. When SW1 is released, C1 will discharge through R1 and the LED causing it to gadually fade out.

Making Electronic Circuits

Connecting Resistors Together

Connecting Capacitors Together

RC Circuits (Resistors & Capacitors)

Questions and Comments on the Electronic Circuits