Adding Chime to 45 minute Counter on Reset

[11flint]

Hello to all, and many thanks in advance for any assistance.

I built a 45 minute timer for a friend using 4510 BCD counteers, 4511 decoders, some NOT and AND gates. To get the minutes to reset on 45, I simply send the correspong outputs to an AND gate, and it resets accordingly.

I need to add a chime to sound on the counter reset, and I was thinking that all I would need is to feed the output of the AND gate responsable for the 45 minute reset into a small signal emittor-ground amp, and get out a little tone from a small buzzer, but that really is not coming together as I would have liked!

It seems that when the AND gate sends the output signal to reset, that I get no voltage on the output pin, which is impossible since the counter does in fact reset! But my multimeter is reading a big fat 0!

What the hell is going on! The output pin of the AND gate shows a steady mV output of around 18-23mV, which does not change when the output is supposed to be high!!! But as I mentioned, something is going on because the counter resets! The output high voltage of the 4002 AND IC I am using should be around 8 volts according to the power supply voltage I am using.

I really am at a lose here. Any insight would be greatly appreciated.

 

[KMoffett]

Could it be that the reset pulse is too short to read on your multimeter? If that's the case, you would need to add a monostable multivibrator to stretch the pulse to a usable length. I've used 555 monostables to pulse a SONALERT, paralleled by a capacitor, to get a very nice decaying-chime sound.

Ken

 

[11flint]

Thanks for that KM! Nice looking circuit! I don't know if the output plse is too short, I am able to measure the input pulses of the AND gate, who's length are the same I presume.

 

[crutschow]

Thanks for that KM! Nice looking circuit! I don't know if the output pulse is too short, I am able to measure the input pulses of the AND gate, who's length are the same I presume.

That's an incorrect presumption. The inputs are the counter pulses, which are long. The reset pulse only occurs when all the counter pulses have become high, and only lasts long enough for the counter to be reset.

 

[11flint]

That's an incorrect presumption. The inputs are the counter pulses, which are long. The reset pulse only occurs when all the counter pulses have become high, and only lasts long enough for the counter is reset.

Well, that actually is very good news then! I will setup the monostable circuit as per KM's design, and give it a go.

 

[11flint]

Nope, it doesn't work. What's the voltage rating on the buzzer? Funny enough, the buzzer chimes when I power off. Must be the discharge voltage.

 

[crutschow]

Nope, it doesn't work. What's the voltage rating on the buzzer? Funny enough, the buzzer chimes when I power off. Must be the discharge voltage.

Does the monostable sound the buzzer if you momentarily apply 5V to the trigger input?

If so then the reset pulse may be too short to trigger the monostable. You might try reducing the 10kΩ transistor base resistor to 2kΩ or so.

 

[11flint]

No it doesn't. It does though when I apply 5v to pin 3 (ouput), actually buzzes, and stays on till I apply 5v to to ground of the 555. I'm guessing I didn't build the above circuit correctly.

 

[11flint]

Yeah, looking back over the circuit I built last night, the errors are obvious. Obviously the buzzer went off when applying voltage to pin 3, I was turning on Q2.

 

[KMoffett]

It's been a while since I used that circuit, so I went back and bread-boarded it to see if I made mistake. Worked OK, but it was meant to take a input that was high longer than the monostable pulse... a leading-edge trigger. I modified it, to simplify it for your purpose. The output tone depends a lot on the particular electronic tone annunciator you use. A Sonalert works great with a nice decaying chime tone. Another 5V annunciator from my junk box gave a rather unpleasant rising tone on decay.

Ken

 

[11flint]

It's been a while since I used that circuit, so I went back and bread-boarded it to see if I made mistake. Worked OK, but it was meant to take a input that was high longer than the monostable pulse... a leading-edge trigger. I modified it, to simplify it for your purpose. The output tone depends a lot on the particular electronic tone annunciator you use. A Sonalert works great with a nice decaying chime tone. Another 5V annunciator from my junk box gave a rather unpleasant rising tone on decay.

Ken

Thanks Ken! Will give the new cicruit a spin tonight!

 

[11flint]

Yes SIR!!! Works like a charm )) I can't thank you enough Ken!

 

[KMoffett]

Happy that it does what you need. I used that as a "pleasant" alarm on a hospital ICU nursing unit.

Ken

 

[11flint]

Nice! I might suggest that to my mom! She's a nurse in the ICU