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How Do I Read a Motion Detector Schematic?

By R. Dhillon
Updated May 16, 2024
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If you want to build your own home security system, you need to know how to read a motion detector schematic. This displays all of the required components for building the motion detector circuit and shows how those components are connected to one another and the power supply. Such schematics are read just like any other schematic, since they use the same symbols. If you haven't read a motion detector schematic before, you can do so by learning to identify the components by their symbols and how complex components, such as integrated circuits (ICs), are identified. You'll also need to learn to identify the power supply and be able to piece together schematics for areas where some of the components are connected to one another indirectly.

Almost every schematic uses the same symbols to identify components. You can learn to identify these by using a beginner's electronics book or an online chart. When looking at the symbols, you should notice that lines protrude from one or more ends of the symbol. These lines represent a component's leads or pins. Occasionally, there are small variations in the symbols used in a schematic. For example, a resistor can be represented by either a zigzag or rectangle.

It is common for a motion detector schematic to include complex components, such as ICs. ICs, which are sometimes referred to as chips, are typically represented by rectangles and triangles. If you see a triangle, it means the IC is a specific type called an operational amplifier (op-amp). Each IC is also identified with a model name that typically consists of numbers and letters. The model name allows you to look up the IC and purchase the correct component.

The sensors, such as passive infrared (PIR) sensors and cameras, in a motion detector schematic might also be identified by rectangles. In some cases, the designer of the schematic might use a special symbol that he or she has designed. Typically, the sensors in a schematic can be identified by their part numbers or model names. If a part number is given, look it up in the circuit's parts list.

Usually, three or more pins of an IC or sensor are connected to other components. In a motion detector schematic, these pins are typically identified by their numbers, and sometimes by their functions. If a schematic identifies pins by their functions, you'll need to locate the component's datasheet, which should be available from the component's manufacturer. Occasionally, the pin numbers are listed out of order in a schematic, so it is important to pay close attention to the locations of the numbers.

Like all schematics, a motion detector schematic uses solid lines to indicate connections between components. It is common for the lines in a schematic to overlap, especially when one shows the design of a complex circuit. For example, you might notice that a series of horizontal lines are overlapping a series of vertical lines. The intersections of these lines don't always represent connections. Typically, a circle is used to identify connections between overlapping lines.

For an electronic circuit to function, it must be connected to a power supply consisting of a ground, also called earth, and a positive voltage. The ground is typically represented by three horizontal lines and the positive voltage is usually represented by a plus sign. Schematics also indicate the type of power required, such as direct current (DC) or alternating current (AC), and the number of volts required for proper functionality. The power supply is often displayed at the top or on the left side of a schematic.

Large motion detector schematics might be broken up into several chunks within a page or across several pages. You can determine how the pieces of the schematic come together by looking for symbols, numbers, or words on the lines representing the connections. For instance, the first part of a schematic might contain an IC with numbered pins and the second part might contain additional components with numbered lines going into those components. In this case, the numbers represent the IC's pins.

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