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External hardware is not strictly within the scope of Beltower software, but a few hints are offered here.

Proximity detector sensors, which respond to changes in the resonance of a tuned circuit, are amongst the most reliable for tower bells.  

A new design developed by Aidan Hedley, using a TDA 0161 chip, is illustrated below.  

Wiring Diagram

  from STMicroelectronics with amendments
wiring diagram
The receiving circuit could be the timer section of the Old Design - see below.

Internals

  of the detector circuit
internals

The IC is a TDA0161 available from Farnell (see http://uk.farnell.com: search for part number 146-7823).   It is easy to use and has a 1/10mA current loop output.

Interfacing is two wire into a simple resistor transistor current to voltage conversion and a series LED will give supply/activation indication.

Performance is excellent - the activator is detected from 60mm, a sheet of aluminium will not be detected until within 15mm.

Components


C1:   680 pF
C2, C3: 1nF
R1:   10 K
L1:   Coil 20 turns 0.25mm wire supported on T0220 mounting washers and nylon screws.

The Finished Product


side view front view

Further details can be found at http://www.st.com/internet/analog/product/75594.jsp   from   STMicroelectronics.

Timer Circuit


The receiving circuit could be the timer section of the Old Design, from and including R3 and the LED through to R6 at the ouput, and the whole thing could be built on a larger board inside the casing.

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    Proximity Sensor Design and Construction

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