Touch Controlled Capacitive Sensor Circuit

Touch Controlled Capacitive Sensor Circuit

Touch Controlled Capacitive Sensor Circuit #2
Part List
Circuit Project Description

The circuit was specially designed for shop windows animation as it makes use of a capacitive sensor that is triggered by touch control system.

Terminology BC337 – a small signal NPN Silicon AF medium power transistor used for general purpose switching and amplifying applications with features such as TO-18 manufactured package, suited for AF driver stages and low power output stages, and divided into three group types Circuit Explanation

The circuit may be placed in a banner in the shape of a post card where the capacitive sensor is placed behind it, as the shop windows gets animated by this circuit. The sensor can be made of a thin sheet aluminum or copper with dimensions at approximately 15×10.5 cm, similar to eh size of a post card and be glued at the rear. Inside the shop window, the card is placed against the glass. By placing the hand of the visitor on the card from the outside, it can activate the relay with single pole dual throw 220 V at 2 A switch and a coil voltage of 12 V at 200-300 Ohms.

The relay is by driven by a super Darlington configuration that is made up of Q1, Q2, & Q3, to provide high impedance. It amplifies the 50 Hz and 60 Hz frequency coming from the alternating current mains supply. This frequency is induced by the human body on the capacitive sensor. The switching of the relay is ensured in an orderly manner by the combination of C1, D2, & D3.

The power supply of the circuit may come from any commercial transformer that can be plugged in to the wall sockets as long as it can supply the necessary voltage and current to power the relay of choice. To achieve this, the transformer adapter should have a smoothing capacitor and a rectifier. The grounding of the circuit is hooked up in a capacitor with a small value but high-voltage rating, which is located to one side of the mains supply socket where the right side holds the live connection. This is to ensure the proper operation of the circuit.


The touch controlled capacitive sensor circuits are suitable in toy shops where it can be used to activate small electric racing cars, lighting equipments, model trains, and other similar plaything. This can serve as an added attraction on the shop window in any holidays especially Christmas. There are advanced designs that are also useful in automation applications and any applications that require the monitoring and measurement of a conductive target by its position, dynamic motion, thickness, non-conductive thickness, and assembly testing.

In oil refineries, capacitive sensors are used to measure the percent of water in oil and in grain storage facilities where the moisture content of wheat is being measured. In homes, the soft-touch dimmers are operated by a cost-effective capacitive sensor while it provides aid to home craftsmen with wall stud sensors and digital construction levels. In laptop computers, the two dimensional cursor control uses capacitive sensor while in retail kiosks, the touch screen monitor is also using transparent capacitive sensors.

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