Single chime circuit

[rogs]

Glad you've got it working OK!

Several 'tweaks' possible to change the sound envelope slightly.
To reduce the 'max active' time you could reduce the 1 meg resistor value slightly - say between 470K and 680K. Makes the 'decay' start faster.
To reduce the actual decay time, reduce the value of the 100K resistor across the 10u capacitor ( not the 100K resistor in series with pin 16). Try 68, 56, 47 or even 33K?

Increasing the resistor value of the 1K, in series with the !N4148 diode, would make the 'ping' more gentle.

You might like to try reducing the value of the 100nF capacitor between pins 7 and 2/3 of the 571. I've used it as low as 10nF in the past. Changes the feedback gain slightly, and affects both the amplitude and sine purity.

Minor value changes like this allow you to 'tune' the chime to your needs.

 

[KMoffett]

I just ran across this thread, and have to go back and through in a relay solution for the all-relay Jeopardy game chime. The attached is a relay monostable that would be used to pulse the chime solenoid when the responding contestant's relay is closed and held.
The pulse width depends on the relay's coil resistance, the relay's dropout voltage, and the size of the capacitor. It's old technology, but it does work well.

Ken

 

[Gabe]

Ok, I put this on a board and have an issue. I *think* it's in the tone generation part, because when I hit the trigger, I can hear a barely audible hiss (I have this hooked up to an amp to test it) that fades away at the same rate as the tone would, but I don't actually hear the tone.

I haven't etched a board in a long time, so I bought a perfboard at Radio Shack. I hate those things, but it's all I have to work with right now. I'm sure there's some FUBAR in there that I created, but I'm not sure which part of the circuit to study.

Thanks!

UPDATE: I didn't have the 100nF cap connected to pin 14 on the 571, so I fixed that. When I did, the fading hiss went away, but I still get no tone. I love multiple failures

 

[Gabe]

To all the people sending in solenoid-based suggestions - I wish I would've asked when I first made this! Truth be told, though, the doorbell never lived up to expectations. It was too quiet when in a large room, and I always had to put a mic next to it, which was cumbersome. This solution that Rogs has sent generates a tone that I can send directly to the house audio (I use this at conferences) so that everyone can hear.

I only make this comment in case someone else finds this thread and decides to go the doorbell route. If you just want this in your basement, it would work fine. If you're in a big room at a school or bar or conference, though, you need to find something that's easy to amplify.

 

[rogs]

And I thought it was going so well.....!

571 has two identical halves. One half (pins 1-8 we are using as a twin 'T' sine wave oscillator. Should run all the time. The output is taken from pin 7, as an audio input to the gain cell (pin 14) of the second section (pins 9 -16), which is used as a VCA (Actually, strictly speaking it's a current controlled amplifier, but that's just going to confuse the issue here!!)

Sounds as if the oscillator is not running. Check that you have the twin 'T' components connected correctly (3 x 22nF caps, 2 x 15K resistors, and 1 x 1K5 resistor). It's easy to miss a ground connection here.

Check you have the 100nF capacitor connected between pin 1 and ground.

Try a different value for the capacitor between pin 7 and pins 2/3. (Say another 22nF for example).

The oscillator has always been pretty reliable in my experience (the circuit has been used several hundred times!), so it sounds like a faulty connection somewhere.

To test that the oscillator is running (I'm guessing you don't have access to an oscilloscope at the moment?) connect pin 7, via a capacitor (100nF will do) to the input of your amplifier. There should always be a tone present, regardless of the 'trigger' condition.

(Don't forget to check that both pins 4 and 6 of the 571 are grounded, by the way. And that pins 2 and 3 are linked. Easy to overlook!)

 

[Gabe]

I thought that section had something to do with it (with the symmetry and all), so I've gone over it probably 10 times. I guess 11 & 12 won't hurt, though

Still, I'm 99.9% sure I've got that section correct, but the proof is in the pudding, I guess. I'll check again.

It seems odd that I heard that decaying hiss until I connected that 100nF cap to pin 14, then it went away. It was definitely a hiss that decayed when the trigger was...well...triggered. I did it 3-4 times just to be sure. The only sound I hear now is a slight 60 cycle hum (which I had on the breadboard until I connected pin 13 to +12v, which was the first thing I looked at here, too).

Oh, and by NO MEANS do I doubt your circuit! Hell, it worked once already for me. I'm 100% sure this is me...

Another update:

A 100nF cap across Pin 7 and the high side (not the grounded terminal) out to the amp does result in a tone. Does that mean that 'T' section is ok?

I know I'm in my 30's with two kids because I now can't wait to work on my electronics project on a Friday night instead of...you know...going out.

 

[rogs]

Not quite sure what you mean by 'high side'. I was thinking of simply taking the output, via a capacitor directly to the amp input positve, with the amp input negative connected to gnd. No connection to the circuit audio out.

Any way,does sound as if the oscillator is running.

Remake the connection between pin 7 and pin 14 with the 100nF, and we'll try 'forcing' the VCA on.

Connect the junction of the 1n4148 cathode and the 1K resistor dirctly to 12V. That should force (and keep) the voltage controlled amplifier at maximum gain. Do not try the same thing from the other side of the diode. You'll probably destroy the 4093!!
If that forces that sound on, we need to look at the trigger circuit.

 

[Gabe]

Sorry, I forgot "high" is logic term. I was just typing what was in my head as I was going through the schematic - the positive audio connector is the one on the top of the schematic - the "higher" one There was no connection to the circuit, though.

Anyway, connecting the junction between the diode & resistor to 12v did make it hum a bit louder, but there was no tone. I'll check that section some more.

I take that back - I do get a tone. Now I need to find out why I didn't before...

 

[Gabe]

All right! It's this damned perfboard. Well, really it's my soldering on the perfboard, but if I would've made a board I wouldn't have to do it this way, so I'll blame in on that. I cleaned up my solder connections. It looks like the 12v that I was connecting to that diode/resistor junction didn't have a good connection, and that was the 12v going into the trigger section.

I hear a little bit of a hum or distortion right after I hit the trigger, like vvvvbeeeeeeeeee (with vvvv being the noise, and beeeeee being the tone), but I didn't on the breadboard, so I'll chalk that up to soldering as well.

With that, I guess I'll clean up my solders and call it day.

Thank you so much for your help. If you're by any chance near Chelsea (London, in case there's more than one), I'd be happy to buy you a beer in a few weeks!

 

[Gabe]

Hi guys, sorry to revisit this old post, but I'm having an issue with this thing and I hope you can point me in the right direction. The trigger sets off the ding all right, and by and large it behaves perfectly, however there is a background buzz going on all the time. I recorded a couple seconds of it: [video]http://dl.dropbox.com/u/51030/buzz.mp3[/video] (apologies for the background talking...this was with my phone).

My only guess is power, so that's the route I'll take for now, but if you guys have any thoughts, I'd love to hear them!

Thanks,
Gabe

 

[KMoffett]

Please post the circuit you are using.

Ken

 

[rogs]

Assuming you are using the circuit I sketched out in post #6, try the following, and see if any (or more) of these options stop the 'buzz' .

Try them one at a time.

Remove the capacitor connected to pin 14 of the 571 ic.

Remove the in4148 diode connected to the 4093 output

Remove the capacitor connected to pins 2 and 3 of the 571 ic.

Do any of those actions stop the buzz - and if so, which one?

 

[Gabe]

That is the same circuit. I will try that. Thanks!