Polyphonic Doorbell (September 2003)

Title basically says it all

Postby thomas » Wed May 30, 2007 12:00 am

I have built the following project but it still is not working correctly. It does the following
It will play a tune when first powered up and then again if you press the switch quickly.

If I check the VDD and MCLR pins with a multi meter you can see the power go off to 0v after the 1st and 2nd times but after then the PIC does not switch the power off and it stays at about 5v. If I power the circuit off and wait it will work again.

I built a MCLR circuit to Microchip's spec but this does not seem to have helped.

All of my capacitors in the circuit are rated at 10v but the 1uf caps are rated at 63v as I can't get any that are lower voltage, does this make any difference?
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Postby cosmicbob » Wed May 30, 2007 12:00 am


"caps are rated at 63v"

Using a cap with a higher voltage rating won't hurt or change anything. The only consideration when using a higher voltage cap is that they are usually bigger physically. In another(different) circuit the voltage won't matter either but the size may restrict what you can use.


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Postby philip987 » Wed May 30, 2007 12:00 am

When you say the PIC fails to switch the circuit off check at pin2 of IC1 and see if the signal goes low there. If it stays high I would bee looking for a short on that track to Vcc. I f on the other hand the signal goes low then your problem lies in the transistor circuit. Does the collector of T2 change state to a high. Dare I say, have you triple checked that all your resistor values are right

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Postby thomas » Wed May 30, 2007 12:00 am

Thanks Philip

I have checked that the resistor values are correct. I will check for shorts or check the transistor circuit. I have checked that the pin outs of the transistors are correct with one of those peak component analysers.

Will post more when I have done some more investigation

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Postby fredmond » Wed May 30, 2007 12:00 am

Thomas it's not you mate it's the project itself, they obviously havn't tested it properly, very erradic behaviour, will play a succession of tunes and then hang, each time it completes a tune pin 2 goes low but before it zeros out it bucks it up again to play the next tune, many other problems, I have to admit that the design is a brilliant concept but in it's present state is unworkable, I believe the problem is the firmware itself, although i shouldn't have too i will have a look given some time and see what i can do, although i distaste the idea of trying to follow somebody elses other than my own code, will post back if i find a cure.
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Postby s1d3k71 » Wed May 30, 2007 12:00 am

I've tried this circuit, and it doesn't play even a single sound. I used 16f84a because 16f84 is hardly available, I recompile the source code, and programmed it into pic.

Do you guys have other sample code that's works.
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Postby mmani » Sat Jan 19, 2008 12:00 am

s1d3k71 even i used pic16f84a instead of 16f84
even my circuit does not work
now i am checking out entirely hope if i find some fault i well tell u
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Joined: Thu Jan 02, 2014 10:40 am

Re: Polyphonic Doorbell (September 2003)

Postby supravat » Wed Nov 19, 2014 2:48 pm

I want to make polyphonic doorbell project which is appeared elektor sep 2003 issue.But I am facing a problem while programming the microcontroller pic16f84a the hex file which is given not include the fuse setting.Wll anybody help me for correct fuse bit for pic16f84a?I am waiting to receive a reply in forums.
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