I need some help creating a circuit that takes 12V of power for half a second and then uses that power to

beep
*wait half a second*
beep again

And to do this whenever power is applied for one second.

This circuit should not have a constant power supply for it to work. So I am unsure on how to make this work.

Can anyone help me? Thank you.

 

Not a big problem. How much power is available when the 12 V is on, and what are the specs for the beeper. How long are the beeps? If you don't have one picked out, how loud does it have to be? Quiet room, shopping mall, football game...

Also, where are you located, what is your skill set for building a small circuit, and what kinds of components do you have or have access to?

First thoughts, one CMOS logic chip or a one-chip transistor array that makes three time periods (first beep, 0.5 s delay, second beep), some resistors and capacitors, maybe a transistor to drive the beeper, some perf board, a 12 V input connector, maybe an enclosure of some kind.

ak

 

Still missing lots of information about the project, but here is a first pass.
R1-C1 times the first beep.
R2-C2 times the delay between beeps.
R3-C3 times the second beep.
Beeper current must be less than 10 mA.

There is a more complex version where a single timer is used for both beeps, triggered by both the initial power-on and after the delay. This is handy if having a single adjustment point for both beeps is important.

Depending on how long power is off between cycles, the circuit might need two additional resistors to shorten the reset time.

ak

 

Not a big problem. How much power is available when the 12 V is on, and what are the specs for the beeper. How long are the beeps? If you don't have one picked out, how loud does it have to be? Quiet room, shopping mall, football game...

Also, where are you located, what is your skill set for building a small circuit, and what kinds of components do you have or have access to?

First thoughts, one CMOS logic chip or a one-chip transistor array that makes three time periods (first beep, 0.5 s delay, second beep), some resistors and capacitors, maybe a transistor to drive the beeper, some perf board, a 12 V input connector, maybe an enclosure of some kind.

ak

About 2 amps are available when 12V is on.

The beeper https://www.radioshack.com/products/radioshack-102db-piezo-siren
The two beeps should sound for 250 ms with a 250 ms delay between them.
It should be as loud as it was intended, 102db.

I am in Washington. I have access to a soldering iron, some basic parts. I can order online or buy from radioshack if needed.

Thank you.

 

Actually I will be using this one instead https://www.radioshack.com/products/radioshack-76db-piezo-buzzer

So the beeps should be 76db

 

Changing R1 and R3 to 240 K should get you those times.
To wring the last bit of loudness out of the circuit, U1C and U1D can be replaced by a 2N7000/7002.
What is the minimum *off* time between 12 V pulses?

ak

 

1 - 2 seconds

 

In that case, add a 10K ohm resistor in parallel with C4. This will discharge C1 and C2 when the power is disconnected and the caps would be floating, to assure that those two timers start with discharged caps every cycle. C3 is reset by U1A.

ak

 

In that case, add a 10K ohm resistor in parallel with C4. This will discharge C1 and C2 when the power is disconnected and the caps would be floating, to assure that those two timers start with discharged caps every cycle. C3 is reset by U1A.

ak

VCC is the positive from the power source, why is positive connected to + and - of the buzzer?

So the power source branches off into multiple wires to connect to each vcc point? Or only ground branches and positive is connected straight to the + of the buzzer?

 

Standard schematic shorthand - all identically-named nodes are connected. All Vcc points are connected together and all ground-symbol points are connected together. AND, the chip's power pins are not shown. Back when large schematic pages had hundreds of gates, not showing any device power and ground pins removed a ton of clutter. That is a common practice today. U1 pin 14 goes to Vcc (actually Vdd) and pin 7 goes to ground (actually Vss).

The + pin of the beeper goes to Vcc. The - pin of the beeper is connected to U1C and U1D output pins in parallel. Why do you think both beeper pins are connected to Vcc?

ak

 

Standard schematic shorthand - all identically-named nodes are connected. All Vcc points are connected together and all ground-symbol points are connected together. AND, the chip's power pins are not shown. Back when large schematic pages had hundreds of gates, not showing any device power and ground pins removed a ton of clutter. That is a common practice today. U1 pin 14 goes to Vcc (actually Vdd) and pin 7 goes to ground (actually Vss).

The + pin of the beeper goes to Vcc. The - pin of the beeper is connected to U1C and U1D output pins in parallel. Why do you think both beeper pins are connected to Vcc?

ak

Before R1, R2, and R3 is VCC which eventually goes to the - pin by following the circuit.

 

Oh I see what you mean now.

 

In that case, add a 10K ohm resistor in parallel with C4. This will discharge C1 and C2 when the power is disconnected and the caps would be floating, to assure that those two timers start with discharged caps every cycle. C3 is reset by U1A.

ak

Since 2 amps are available, would my resistors need to be rated for 24 watts? That doesn't seem right

 

Since 2 amps are available, would my resistors need to be rated for 24 watts? That doesn't seem right

It isn't. If you combine Ohm's Law: E = I x R

with Joule's Law: P = I^2 x R

You get Watt's Law: P = E^2 / R
Power dissipated in the resistor equals the square of the DC voltage across the resistor divided by its resistance.

For a 10 K resistor across 12 V, P = 144 / 10,000 = 14.4 mW. For good reliability practice, a resistor should not dissipate more than 1/2 its rating. In this case, anything rated above 50mW will be fine. Small through-hole resistors are usually rated for 250 mW.

ak

 

Don't forget 0.1uf bypass cap across IC power pins and diode across buzzer.

 

Don't forget 0.1uf bypass cap across IC power pins and diode across buzzer.

C4 is on the schematic. The beeper is a self-oscillating piezo, and doesn't need one. Besides, hanging a cap on the CMOS output stages increases the transient current at each transition.

ak

 

C4 is on the schematic. The beeper is a self-oscillating piezo, and doesn't need one. Besides, hanging a cap on the CMOS output stages increases the transient current at each transition.

ak

Then C4 is too big. Needs to be way smaller.or place a smaller one in parallel

 

No, it doesn't. In fact, this circuit will work perfectly without *any* decoupling, but that's another thread.

Decoupling a digital logic gate is much easier than an analog part, and CMOS is very tolerant. 0.01 uF is probably too small for the newer high speed bus driving parts, but just about anything will stabilize a jelly-bean part; their edge times aren't fast enough to cause an internal instability and they have a high output impedance. In fact, a 1.0 uF ceramic is a much better general purpose everywhere decoupler, but back when decoupling became a thing they were much more expensive than the 0.1. uF parts so the smaller ones became the "standard". For this circuit it does not matter at all to the 4093, a larger decoupler is better for a switched 10 mA load if the power source is iffy, and it's always better to reduce the number of different component types if the design supports it.

In the 90's and 2000's, Intel published some excellent app notes on how to condition power for their big processors. These were decoupling design bibles, with a rigorous engineering method for putting the right capacitor in the right place for the right reason. As such, they also taught (not explicitly) how little decoupling might be needed for other parts in other applications.

In the 60's when Ampex started incorporating digital logic chips into their audio and video products, their standard decoupler was a 0.01 uF 10 V cap on every other part, and the power routing on those old boards was *horrible*. And yet, the MTV video jukebox ran around the clock.

ak