An electrical signal is a changing pattern of voltage or current that carries information or triggers an action. Every time you flip a light switch, send a text, or feel your heart beat, electrical signals are doing the work. They exist in two broad forms: the continuous waves found in nature and older electronics, and the discrete on-off pulses that power modern digital technology. Your own body runs on electrical signals too, using tiny voltage changes to fire neurons and contract muscles.
How Electrical Signals Work
At the most basic level, an electrical signal is a voltage that changes over time. That change is what makes it a “signal” rather than just a static charge sitting on a battery terminal. The pattern of change, whether it rises and falls smoothly or snaps between two fixed levels, encodes information. A microphone converts sound waves into a smoothly varying voltage. A computer processor encodes data as rapid switches between high and low voltage states. In both cases, the underlying principle is the same: a controlled change in electrical energy represents something meaningful.
Electrons themselves move through a wire surprisingly slowly, drifting at only a fraction of a centimeter per second. But the electromagnetic wave that pushes them along travels close to the speed of light, which is why a lamp turns on the instant you hit the switch. Think of it like a long tube filled with marbles: push one marble in at one end, and a marble pops out the other end almost immediately, even though no single marble traveled the full length.
Analog Signals: Continuous Waves
An analog signal is a smooth, continuously varying voltage, typically shaped like a sine wave. It can take on any value within a range, not just specific steps. A vinyl record stores music as an analog signal: the grooves physically mirror the shape of the original sound wave, and the turntable’s needle translates those grooves back into a continuously changing electrical voltage that drives a speaker.
Analog signals represent physical measurements directly. Temperature sensors, old-fashioned radio broadcasts, and the electrical activity of your heart all produce analog waveforms. The strength of the signal (its amplitude) and how quickly it cycles (its frequency) together describe what’s being measured. The tradeoff is that analog signals pick up noise easily. Any stray electromagnetic energy in the environment gets added to the wave, and once it’s there, separating the original signal from the noise is difficult.
Digital Signals: Ones and Zeros
A digital signal represents information as a sequence of discrete values, almost always the binary digits 0 and 1. Instead of a smooth sine wave, a digital signal looks like a square wave, snapping between a low voltage (representing 0) and a high voltage (representing 1). Every photo on your phone, every streamed song, and every website you visit is encoded this way.
The major advantage of digital signals is resilience. Because the system only needs to distinguish between two states, high or low, small amounts of noise don’t corrupt the data. A slightly distorted square wave is still clearly “high” or “low.” This is why digital audio doesn’t degrade the way a cassette tape does after repeated plays. The tradeoff is that converting a real-world analog measurement into digital form always involves some approximation, since a continuous wave must be sampled at specific intervals and rounded to the nearest available value.
Electrical Signals in Your Nervous System
Your body generates its own electrical signals, and they work differently from anything in a wire. Neurons communicate using brief voltage spikes called action potentials. At rest, the inside of a nerve cell sits at roughly negative 70 millivolts compared to the outside, a tiny charge maintained by an uneven distribution of sodium and potassium ions across the cell membrane.
When a neuron receives enough stimulation to hit its threshold, channels in the membrane snap open and let positively charged sodium ions flood inward. This rapid influx drives the voltage from negative 70 millivolts up toward positive 30 or 40 millivolts in about one millisecond. That swing of roughly 100 millivolts is the action potential. It’s an all-or-nothing event: the neuron either fires completely or doesn’t fire at all. There’s no half-strength nerve impulse.
Almost immediately, a second set of channels opens to let potassium ions flow out of the cell, dragging the voltage back down. The whole cycle, from resting state to spike and back, takes just a few milliseconds. This pulse then triggers the next stretch of membrane to fire, sending the signal racing along the nerve fiber toward its target, whether that’s a muscle, a gland, or another neuron.
How Your Heart Uses Electrical Signals
Your heartbeat is coordinated by a specialized electrical signaling system. It starts in a cluster of pacemaker cells called the sinoatrial (SA) node, located in the upper right chamber of the heart. These cells spontaneously generate an electrical signal about 60 to 100 times per minute without any input from the brain.
That signal spreads across both upper chambers (the atria), causing them to contract and push blood down into the lower chambers (the ventricles). The signal then reaches a second relay point, the atrioventricular (AV) node, which deliberately slows conduction for a fraction of a second. This brief pause gives the ventricles time to finish filling with blood. The signal then travels along specialized fibers in the walls of the ventricles, triggering them to contract powerfully and pump blood to the lungs and the rest of the body. The ventricles relax, and the cycle starts again at the SA node. An electrocardiogram (EKG) is simply a recording of these electrical signals picked up through the skin.
Measuring Electrical Signals
Engineers and technicians visualize electrical signals using an instrument called an oscilloscope, which plots voltage on the vertical axis and time on the horizontal axis. The result is a real-time waveform that reveals everything important about a signal: how strong it is (amplitude), how fast it cycles (frequency), and whether it’s behaving as expected or showing irregularities.
Oscilloscopes can be tuned for sensitivity. The vertical resolution determines the smallest voltage change the instrument can detect, which matters when measuring faint biological signals like those from nerves or muscles. The horizontal time base controls how finely the instrument slices time, which is critical for capturing extremely fast pulses in digital circuits. By adjusting these settings, the same tool can analyze anything from a slow heartbeat waveform to a billion-cycle-per-second processor clock.
Signal Quality and Noise
No electrical signal exists in perfect isolation. Noise, unwanted electrical energy from nearby circuits, radio waves, thermal vibrations in components, or even the amplifier used to measure the signal, inevitably gets mixed in. The standard way to quantify how clean a signal is uses a metric called the signal-to-noise ratio (SNR), expressed in decibels (dB). A higher number means the useful signal is much stronger than the background noise.
In practical terms, an audio recording with a high SNR sounds crisp and clear, while a low SNR recording has an audible hiss or hum. In medical devices like EKG monitors, a poor SNR could obscure the very heart rhythms a doctor needs to see. Engineers manage noise through shielding cables, filtering out unwanted frequencies, and using digital encoding, which is inherently more noise-resistant than analog transmission. Understanding that every electrical signal exists on a spectrum from “pristine” to “buried in noise” helps explain why signal processing is such a large field in both electronics and medicine.