Information on Abel simulator sensors.

The Abel bell ringing simulation program for PCs is written by Chris Hughes and Simon Feather. More information may be found at http://www.abelsim.co.uk.

Sensing the position of the bell.

In order to detect the position of a (silenced) swinging bell, a sensor is used. This detects a "target" on the wheel of the bell and sends this signal to the simulator which can then make the bell sounds.

Two types of sensor are commonly used, one which uses a proximity detector circuit (designed by Aidan Hedley), and one which uses an optical "photohead" to detect light back from reflective tape on the wheel.

The two target method.

There are two methods of setting up the sensors. The first of these has two targets, one positioned to give a signal when the clapper would normally hit the bell at handstroke, and one for backstroke. It is possible for the simulator to mis-count the pulses and ring at the wrong time in the swing. The tapes are positioned to give the correct signal when the bell is rung full circle only. Setting the tapes up to strike at the correct time without any oddstruckness can be difficult. If the bell is rung faster (ie lower), it will appear to strike later and later until it stops striking completely.

The delayed (single target) method. 

The second method uses a single target positioned to give a signal when the bell is mouth downwards. An electronic circuit then delays the signal until the bell is at the point in its swing when the clapper would hit the bell.  Any adjustments in this delay to make the bell strike at the correct time are made from the simulator itself. This system can never get out of step, and it is also possible to simulate raising and lowering the bell (apart from chiming). It is the method used by the "multi bell interface" for use with a PC running Abel or the Ringleader simulator.

Sensors.

There are two main types of sensor, inductive and optical. The inductive design is published in the Abel documentation, but the integrated circuit it uses is now very difficult to obtain. It also has a very short operating range, but will operate in all light levels.

The circuit I use for optical photoheads sensors is as shown:

The reflective tape is self adhesive and is placed on the wheel of the bell, and the output is "low" when the reflective tape is detected. This will work well in all but high light levels at up to a distance of about 8"-10" (providing D1 and Q1 are well aligned and side by side). The value of R4 adjusts the sensitivity, increase its value for longer ranges, but this also reduces its performance in high light levels.

This circuit is placed inside a small plastic tube mounted on an aluminium bracket. The 50p piece gives some idea of its compact design.

Interfacing to a PC or Ringleader simulator.

Both Abel 3 and the Ringleader can be connected to all the bells in the tower using a "multi-bell interface" (MBI). This is a junction box in the belfry into which all the sensors are connected and it makes use of the delayed (single target) method of sensing the position of the bell.

The MBI contains a small microprocessor which scans the sensor inputs rapidly, and when a sensor is activated, it starts a timer. This timer counts in 1/100ths of a second steps and after a pre-programmed duration, it then sends a signal (via a RS232 serial interface) to the simulator. There is one timer for each bell and the value the timer stops at is set over the serial link from the simulator.

The MBI comes in versions for 6, 8, 10 or 12 bells, and when all the bells are connected in this way, it provides a facility for a completely "silent" practice. It is still possible using the MBI to ring just one bell with the simulator ringing the rest to use the simulator for developing listening skills.

On PCs without a COM (serial) port, it is possible to use a USB-serial port adapter to connect the MBI to the PC.

Examples of photohead installations.

Fabricated metal low side frame, Ashchurch, Glos

Standard H-pattern frame, Moulton, Northants

Standard low-side frame, Bury St. Edmunds (photo - Tim Hart)

For details of pricing and availablilty, please email me at:-

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David Bagley