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Thursday, 2 October 2008

Church Bell Simulator

The first question bound to get asked is what has this got to do with QRP?

Well 2 years ago I used to commute to London on the train and one of the passengers is the manager of a local (to my QTH) church bell ringing group. (Now I am not the least bit religious having been througha Roman Catholic boarding school kind of drums all religion out of you!)

Anyway discussions on the somewhat boring commute every day had to come to his 'hobby' and that was bell rining, not campanology that is hand bells, and the problems he had when newcombers were first starting out. The noise when they get it wrong or when they ding when someone else should have donged or whatever... when practicing they sometimes silence the clapper (think that is what it is called) anyway I am not into the hobby but what interested me was the option to add some electronic sensors to the silenced bells and the signals from these transducers could be fed into a PC/Laptop and interpreted and the PC/laptop could 'play' the bell. So the worst/best group of bell ringers could ding and dong all they wanted without disturbing Mr & Mrs Grumpy Guts who live near the church and started to complaign about the noise of the bell ringing. Far be it fro me to say that moving next to a Church from the 1500's with bells is not going to mean you will hear bells but the parish council stated the bell ringers had to silence operations or only be active at certain times. I think that is the story it was a long time ago....

The idea is not new and you can read about it here

Anyway enough diversion onto the electronics and radio.

So the sensors on thebelfry are basically IR LED and IR detectors mounted in a little box adjacent to the bells. On the wheel cage the bells sit inside I will attach two (as the bells ding and dong at 2 places when pulled) pieces of reflective tape. As the bell wheel rotates and passes the tape a signal will be created. I use a 555 timer to widden this signal into a +5V pulse of about 50-100ms and this is then fed into a PIC. There will be 8 of these as this particular bellfry has 8 bells so I will use 8 input lines on the PIC.

The PIC then through the magic of code converts the input signals into a series of ASCII data signals that can be input into a PC/Laptop. I'll cover the why in a minute. Enter the qrp bit. The church being a historic monument and all that means that you cannot then put up wires etc to transfer the signals to the PC/Laptop so I have investigated several different ways of doing it and the easiest was to use (in the UK) licence free 433MHz TX and RX modules so the connection is wireless. This adds a bit of complexity as the serial ASCII signals have to be converted to Manchester code to be transmitted and then decoded before being presented as the ASCII code at the PC/Laptop. As side note is I tried Bluetooth and COM port/Modem signals but it just wouldn't work reliably.

Now why an ASCII data stream... the Bell Ringers use a piece of software called ABEL and this allows the connection to external bell interfaces and the signals to be 'read' so that a simulation of the sound can be created.

All sounds good so far...

Well the sensors are the easy bit.
The PIC code is causing a few headaches but it seems to be working for a single signal and I am about to connect up the 433 MHz TX/RX modules.

The bit in the bellfry will be called Quasimodo and the bit in the bell ringers chamber Esmarelda.

More as project progresses.

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