Free circuit diagrams

Bookmark and Share
privacy policy

Capacitive Sensor

Note: For proper operation, circuit ground must be connected via a small value, high voltage-rating capacitor to one side of the mains supply socket. The "Live" side is the right one.

Special design for shop-windows animation
Useful for many types of touch controls

Circuit diagram

R1,R2 1M 1/4W Resistors
R3,R4 47K 1/4W Resistors
C1 10F 25V Electrolytic Capacitor
C2 470pF 630V Ceramic or Polyester Capacitor
D1-D3 1N4002 100V 1A Diodes
Q1-Q3 BC337 45V 800mA NPN Transistors
RL1 Relay with SPDT 2A @ 220V switch
Coil Voltage 12V. Coil resistance 200-300 Ohm
J1 Two ways output socket
Sensor Aluminium or copper thin sheet with the dimensions of a post-card,
glued at the rear of the same (approx. 15x10.5 cm.)
Thin screened cable

Circuit description:
The purpose of this circuit is to animate shop-windows by means of a capacitive sensor placed behind a post-card-like banner. The card is placed against the glass inside the shop-window, and the visitor can activate the relay placing his hand on the card, from the outside. Especially suited for toy-shops, the circuit can activate model trains, small electric racing cars, lights etc. Further applications are left at user's imagination. Adopt it to increase the impact of your shop-window on next Christmas season!
Q1, Q2 & Q3 form a high impedance super-Darlington that drives the relay, amplifying the 50Hz alternate mains-supply frequency induced in the sensor by the human body. C1 & D2, D3 ensure a clean relay's switching. Power supply can be any commercial wall plug-in transformer with rectifier and smoothing capacitor, capable of supplying the voltage and current necessary to power the relay you intend to use.

author:RED Free Circuit Designs,

Link to this page for forums and blogs:
All content on this site is provided as is and without any guarantee on any kind, implied or otherwise. We cannot be held responsible for any errors, omissions, or damages arising out of use of information available on this web site. The content in this site may contain COPYRIGHTED information and should not be reproduced in any way without prior permission from the authors. Be aware! Electricity can kill! © 2008.
page generated in :0.0219