Conversion of motor driven door bell chime to electronic.

[retiredtech]

I have a 40+ year old Nutone 8 chime door bell that is end-of-life. It is a great sounding unit and before I scrap the unit and go out and buy a similar one at $400 plus I was wondering if anyone has built an electronic circuit to drive the solenoids instead of the motor driven mechanism. It would, of course, also require the additional circuitry for timing and interface with the existing 16 VAC power.

Richard

[sghioto]

Doesn't sound complicated at all. It's just a sequencer. Are you needing someone to build a circuit or looking for designs?

Steve G

[haklesup]

First you need to find a way to mount the right kind of solenoids in front of the chimes. Driving the coils should be straight forward.

An SCR can be used as a switch (or a SS relay) and that can be driven by a logic IC, perhaps with a transistor. It would be easier if there was a DC supply for logic, if you really want to go all AC, I'm kind of at a loss as to how to implement a sequencer to drive the solenoids without going back to some kind of motor.

[dacflyer]

i am guessing it is 4 chimes..
perhaps this is a job for a small PIC ?

or perhaps, a dual 555 ( 556 ) timer.. a 1 shot to start it... the 2nd half as the clock pulse for a 4017 ic..
0-3 chimes 4-5 pause 6-9 chimes, you can adjust clock pulses for speed you want.. ( assuming Westminster chimes )
of course you'd need a ac-dc power supply.
what exactly is worn out on yours ?

[dyarker]

retiredtech said 8 chimes, not 4; unless he meant 8 strickes on a smaller number of chime bars.

Not much hardware work to do. There is already a solinoid on each chime bar. They just to get the 16VAC through something other than the motor driven cam contracts. Either triacs, or contacts of small relays with 12VDC coils.

I believe 16VAC should still be used for the door bell buttons with a bit a AC current flowing through the button when pressed. That should make the button contacts last longer. That signal will need conditioning before being connected to sequencer.

The DC power needed by sequencer logic (and relay coils, if that route) is paralelled off 16VAC supply through full-wave rectifier. Pre-regulated to 12V for 5V or 3.3V logic, and relay coils.

A 16 pin microcontroller would have enough I/O for eight relays, and two door bell button inputs. Separate button inputs allow for different tunes for each door.

retiredtech,
How many solinoids?

Cheers,

[retiredtech]

There is physically 4 solenoids that can strike either 4 or 8 times determined by a switch. The solenoids are in place and work just fine. They do not need to be moved. First I would be looking for a circuit that had already been built such as a kit and then go with individual designed circuits. I do not have a problem with building but am a little slow on designing! I am still searching the internet for a possible solution.

Richard

[Lenp]

If it is 8 note front door and 4 note rear door unit, a power supply, a cheap micro, 4 triacs and some small parts is about all that is needed. I would consider opto-isolators for the micro I/O because of the long wire to the buttons and the inductive spikes from the solenoids.
The software code is pretty strait forward and a pot can be user to set the timing of the chimes. A board could be small enough to go inside the existing chime cover.
You can pm me if you want specific help or post here.

[retiredtech]

Thank you all for your comments...
I have stumbled upon a circuit I believe will satisfy my requirements. Take a look at it and see if you agree.
attached is the doorbell circuit labeled doorbell.jpg

[dyarker]

Quik check by eye looks good. Using 1N4001s for D1 thru D8 seems like over-kill, but won't hurt anything.

Cheers,

[Lenp]

That looks like a workable solder logic fix. I see the design also uses isolators for the I/O. The two IC's, diodes and most of the wiring could be replaced with a micro. That would offer the same operation plus the possibilities of adding doors. You could create different melodies and select them with jumper or switches, without changing any wiring. (if you are creative composing tunes with just four notes )
The possibilities are boundless....

[retiredtech]

I noticed there was no designation of a component type for U1. Ideas?

Richard

[sghioto]

A TLP222AF solid state relay will work for U1. From Digikey at only a dollar and eight cents.

I don't see any current limiting resistors for the opto electronics. Since only one MOC3023 is on at a time a single 1.8K ( with a 12 volt supply) resistor from ground to the common connection of the LED cathodes will suffice. You will also need to connect a resistor in series with the LED in U1. Another 1.8K will do either on pin1 or pin2.

By the way I agree with Len, this project is screaming for a micro.

Steve G

[dacflyer]

the circuit you posted, was basically like the one i was describing earlier
the 555 should have some sort of clock adjustment to control speed of the chimes.
you do not want the chimes to play the notes too fast or slow. as for getting the right pause for the chimes, 0-3 is good 4-5 should not be used, then 6-9 for the last bits
this is considering your playing in 1/2 note mode, then your pause would be a whole note count.
if you need more explanation let me know, i'll describe more in detail.
the way the circuit is laid out does look like it plays Westminster chimes.

[sghioto]

the 555 should have some sort of clock adjustment to control speed of the chimes

R5 is the speed adjustment.

Steve G

[dacflyer]

ya, i saw that after i went back and looked at the schematic