It goes on and off with each cycle of the incoming tone.

Note - in this description, C1 is charged "down". That is, as the voltage across it increases, the bottom end moves more and more in a negative direction toward GND because the positive end of the cap is clamped at Vcc. Also - The Trigger input threshold voltage is 1/3 Vcc, but that is measuring up from GND. Measuring down from Vcc, it is 2/3 Vcc. Actually, ( Vcc - (2/3 Vcc )).

The #19 schematic is almost correct. If you move C1 so it goes from the Trigger input to Vcc, then it holds the trigger input is high on power-up, and the monostable is not triggered falsely.

With each positive half-cycle of the tone, the "NPN trigger" (reference designators - !) transistor "Q1" pulls the left side of R2 low and partially charges C1. During the tone negative half-cycles, Q1 is off and C1is partly discharged through the serial combination of R1 and R2, but not enough to empty it. Thus, with each positive half-cycle, C1 is charged up a little bit more through R2. Eventually, the voltage across C1 is greater than 2/3 Vcc, and the 555 is triggered.

ak

 

It goes on and off with each cycle of the incoming tone.

Maybe or maybe not depending on the NPN trigger circuit which we don't have all the details of.
I asked the TS if the output from the trigger was a steady low but did not get confirmation.

 

The #19 schematic is almost correct. If you move C1 so it goes from the Trigger input to Vcc, then it holds the trigger input high on power-up, and the monostable is not triggered falsely.

Correct.

 

If you locate R2 the same as in #19, there is more independence between the two time constants.

ak

 

If you locate R2 the same as in #19, there is more independence between the two time constants.

ak

AK,
Would the circuit input above trigger directly off of the speaker output? With the .75 second delay the timer will only trigger on the longer beep, then what driver can I connect on the output to just close a small relay. I was ordering a few parts to start experimenting and suddenly I'm getting e-mails that the person was hired and asking about a solution. My hobby solution shifted into 2nd gear when I said I could think about something when a question was raised a while ago. I'm reaching out for a few more answers please. Thanks,

 

Would the circuit input above trigger directly off of the speaker output?

I just re-read all of your posts. Nowhere do you say what the speaker output signal amplitude is. If you know the voltage level, either peak or peak-to-peak, please post it. Without it, can't say.

This will be difficult to do with just a meter, because a meter do not measure AC voltage. It converts it to an approximately equal DC voltage, and measure that. That approximation is calibrated at 50 or 60 Hz, and most low-cost meters to not specify a frequency range and tolerance. The two most common frequency bands for piezo beepers are around 2 kHz and 4 kHz, far enough away from 60 Hz to matter.

If the signal amplitude is above 0.7 Vpeak, it probably will work. To test this, add a 1 K resistor in series with the base to protect it from possibly high signal voltages and/or currents.

ak

 

Good monostable circuit.
The application can make a difference. A deaf person can benefit from a chair actuator.
The delay pulse studied with chickens
(4) Chicken Coop Door Opener | All About Circuits

 

With the .75 second delay the timer will only trigger on the longer beep, then what driver can I connect on the output to just close a small relay.
Thanks,

How long does the relay need to be activated?

 

How long does the relay need to be activated?

It’s going across the battery powered wireless doorbell switch contacts so I guess as long as a normal person usually pushes a doorbell. I’m guessing .25 of a second?
AK’s question about speaker output voltage. AK, would an analog VOHM meter reading give me the AC and DC reading that you are asking for during the beeps? If so I’ll have to buy one, since I grew up using analog meters but no longer have any around.

 

It’s going across the battery powered wireless doorbell I’m guessing .25 of a second?

In that case you can probably connect a relay directly to pin 3.
What is the supply voltage for the 555 circuit?
Do you have a particular relay in mind?

 

In that case you can probably connect a relay directly to pin 3.
What is the supply voltage for the 555 circuit?
Do you have a particular relay in mind?

No specific relay in mind. That’s why I’m here hoping to get some part numbers to order from an electronic supplier. I’ll probably use a common wall charging device and a 5v regulator circuit or maybe a common 5v usb device charger to simplify troubleshooting after I no longer support this customer. Thanks for helping.

 

One suggestion is using a 5 volt relay module.
Connect pin3 of the 555 to the "IN" terminal of the module and set the jumper for high level trigger.
Similar to this:

 

I would like to thank this site and all of you that responded quickly when I asked for help with this circuit. I was able to assemble a small circuit to assist a restaurant franchisee, who hired a hearing-impaired employee and needed to automatically signal her when a device sent out a 1 second tone. The device is currently installed, and I'm told it is working as expected.
My test devices are working so well that I'm pushing it off to a guy to supply more if needed. On to other things!
Thank You,
Thank You,
THANK YOU!
This site and some of you are mentioned in part 1.
Part 1

Part 2

to be continued......