How to connect motion detectors to a lamp retroactively

There are various ways in which you can connect a motion detector to a lamp at a later date. The main differences lie in the effort and the required knowledge of electronic circuits, although simple basic knowledge and basic experience in soldering are almost always sufficient.

Suitable types and designs of motion detectors

Motion detectors are divided into three different types based on the method of detection, each with its own advantages and disadvantages. Usually a passive PIR sensor is used for retrofitting a lamp, which directly switches the power supply via a connected relay. Only in some special cases do you need a high-frequency or radar detector – for example, if you want to install a presence detector instead of a motion detector. For a subsequent connection, choose from the following approaches according to your knowledge, the characteristics of the lamp and the amount of work:

  • Pre-assembled and ready to use systems for insertion into a wall socket
  • Ready motion detectors for direct wiring
  • Modular circuits made up of several components
  • Own design of a circuit on a circuit board

For the first two, ready-to-use solutions, you need no or very little knowledge at all and can expect to spend just a few minutes. On the other hand, you have less freedom in certain areas – for example, when mounting the sensor or installing it in the housing of the lamp. The last one, on the other hand, is suitable only for experienced electrical engineers and is recommended only for learning purposes, prototypes or under special conditions because of the high amount of work involved.

Difference between a presence and motion detector

A passive PIR sensor is a component that only registers motion and turns a device on or off for a specified duration during a time delay. A presence detector, on the other hand, is usually based on detection by ultrasound, radar or radio frequency and registers your presence even if you are sitting still and motionless. A PIR sensor is able to imitate this property in only a certain frame by restarting the time frame at each movement.

Basic functioning in case of a subsequent connection

If you subsequently connect a motion detector to a lamp, control usually takes place via the power supply, as with a switch. The sensor uses a data cable to operate a connected relay that opens or closes an electric circuit. If the lamp has another switch of its own, you must therefore switch it on permanently.

Combination with other switches in series or parallel connection

You can expand the functionality of the motion detector by connecting it to other switches. For example, if you switch a light switch in parallel, it will bypass the sensor and allow additional ordinary and independent operation. However, it cannot switch off a lamp that the sensor has activated. If, on the other hand, you use a switch in series in front of the motion detector, you can switch it on or off as desired. However, this variant does not allow you to control the lamp independently of the sensor.

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