Resurection of Capricorn Elctronics "Caroling Christmas Bells"

Bells


Box Front	Box Back	Box Back Hi-Res	Power Supply	Power Connection

Some quick notes addressing feedback I've gotten about this page:

First and foremost, the musical data I've extracted (see below) is not my intelectual property so, no, I won't share it. If I could it would already be posted on this site.

Next, I'm often asked about MIDI capability for the bells. These bells aren't MIDI. There's no place to just "wire in." They're not hard to opperate electronically from a microncontroller, however. So a MIDI interface could be added if you're capable and so inclined - but that is left as a rip-and-replace excercise for the reader.

As seen in the photos above, the power adapter for the bells I have is 12 volts DC at 200 ma with the center positive and outside negative (or ground).

If you have a set of the bells and are having mechanical problems with them (adjusting the clappers, etc.) see the directions in the hi-res image of the back of the box shown above.

For possible electrical problems... Your problem is either a bad power supply, a broken wire, a blown driver chip, a bad bell coil or a bad microcontroller. If all of the bells are effected it's likely the power supply or the microcontroller. If only one or some bells are effected it's probalby wires (which can break when stressed or flexed too much) but it could be the drivers, coils or the microcontroller, depending. If all 6 bells on one of the two connectors has failed it could still be a break in the "common" wire (usually slightly larger than the others) that powers all 6 of them rather than something more sinister.

The power supply is testable with a meter (or replacmenet) and easily fixed with a 12VDC replacment from Fry's, WalMart, Radio Shack, etc.

The wires/coils would have to be checked with a meter. Without a meter, if you're lucky you might be able to check the wires by flexing them various ways in various places hoping to find the break by closing it. If you do find the break you might be able to tape the wires just right or splice in a fix with twisting and electrical tape but soldering in a splice would be best. Not much can be done with the coils unless you know how to rebuild one.

The driver chips (MC1413P data sheet) are soldered in on all the versions that I have seen, making them difficult to test and impossible to fix without soldering tools and skills. If you have a unit with a cartridge, like mine, you can yank the cartridge (the microcontroller) and pull each of the driver inputs high - that should actuate a bell (it might "clank" instead of ring if you actuate it for too long). I wouldn't try pulling any pins high with a soldered in microcontroller, you might cause damage. If you have socketed drivers (which I've never seen, but you could get lucky), you can swap them to see if the problem moves with the chip, replacing the bad one if it does. Elsewise you'll need an osciliscope to see if the pulses going into the driver are coming back out (inverted, I beleve - and ONLY if the bells are plugged in and there are no breaks in the wires!)

There's no way to test the microcontroller per se but if everything else is working, that's probably the problem. If you have an oscilisicope and you have an idea of what you're looking for you can look for pulses that should be ringing the bells being sent from the microcontroller to the driver chips. Single notes can be corrupted (in the microcontroller's "ROM"), individual bits/bells can be damaged or the whole microcontroller can be in la-la land, as mine was. Not that there's much you can do about it if the microcontroller is fried short of replacing it, as I did. Though you could get lucky on ebay and find a unit with bad bells and a working microcontroller and do a transplant.

This is the story of the resurection of a set of "Caroling Christmas Bells" made by Capricorn Elctronics.

Back in the day mom and dad had a set of these bells. During the holidays they'd put 'em out on the front porch and let 'em ring. They were pretty. They were Chrismasy. They were fun. Then they broke. And, alas, parts were lost, fixes given up and they were thrown away.

I got it in my head to replace them. I searched for 'em high and low. I found Capricorn Electronics easily enough, but not a way to buy the bells and no one from Capricorn returned my E-mails. I found online shops with the bells listed "for sale" but with no price - which, when you calll them up to order, means they're no longer available. Swell. Then I went prowling eBay and found several sets.

One set in particular looked pretty good and claimed to be in working order, though you never can tell, and the bidding was a little high... Another set looked less well kept and the seller said something about "they worked fine last year but couldn't be 'tuned' quite right this year." Bidding was naturally low. I took the hit in shipping and bought both sets figuring that A) odds are at least one set will work, B) if both did I'd have spare set for parts in case the other broke like the original set did, and C) if neither worked I'd probably have enough parts between them to salvage one set.

Happily the one set worked spot-on out of the box as advertised. Tah-dah, goal met. The second set however was toast. It didn't just need "tuning" all of the bells just sat there and buzzed as if they might be trying to ring all at once. Further investigation showed that it had a "cartridge" feeding notes to a pair of MC1413 driver chips, each driving 6 of the 12 bells. The hum went away when the cartridge was removed. The driver chips were intact and each bell would ring when it's "bit" was driven (?high?) manually with a jumper wire. But nothing sensible would come out of the cartridge. Popping the cartridge open I found that inside there was just a single chip, a microcontroller of some kind made by Texas Instuments. Which got the ol' creative juices flowing. If there was a way to replace it... And if I could extract the music from the working set... I'd have two working sets... Hmmmmm...

With too many irons in the fire already I almost passed on this project. But as I thought about it I realized that my current 16 bit PIC24F based project had exactly 12 I/O pins free that I was about to tie up. The work was half way done and it would be easier now than later. So I put that project on hold and ran with the bells.

The first step was recording the original bells, which was simple in theory but a little tricky in practice. (*** The extracted data isn't my intelectual property, so I can't share it or it would be posted on this site. ***) I started with a simple adapter to bring my I/O pins out to wires with their ends stripped. Then I added $50 worth of "pico-hook to pico-hook" jumpers from Fry's. Finally I cobbled up some code to read the bits as the working set played them and spew 'em out the serial port where they were record by a terminal program. If I knew then what I know now - namely that the recording could have been able to fit into the PIC's memory - I'd have done it that way instead. Hind sight is 20-20...

The second step was to fit the cartidge with a new microcontroller. I never could figure out what TI chip they used originally. Not that it would have mattered since I'm not versed in TI stuff or set up to program them. So I selected a PIC from the ones I had on hand that would both fit in the cartridge and hold the array of notes to play, a surface mount PIC18F2550. The matchup between the old and new chips wasn't even close. The pins were the wrong type, the pin spacing was different and none of the pin's functions lined up. So I mounted the PIC on "stilts" (two stacked pieces of a popsicle stick) and wired each pin to the corresponding hole one at a time. Simple enough but tedious. Then I added a little code there you have it.

Of possible interest is the way I reused some of the existing holes in the PCB. I typically use a strip of 5 machined socket pins to attach the programmer in my various projects and this was no exception. But I wanted to make it stil fit in the original cartridge case and be sturdy enough to plug and unplug lots during development and debugging. So I cut the traces away from a few existing holes in the PCB, bent the pins in the strip to make 'em line up drunkenly (sort of) and wired to that. Worked like a charm.

I stil have one bell that sometimes rings and sometimes "thunks." That might be the "tuning" the original seller was refering to. Seems like a mechanical problem. And it moves with the bell regardless of which controller is used. I'll be tackling that one of these days... For now, back to our regularly scheduled projects...

The cartridge and driver board.