Need a short beep circuit

ljcox said:

I assume that you were combining them with resistors on the speaker side.

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ljcox said:

BTW, an alternative RC for the timing oscillator would be 0.1 uF and 680 k.

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Kolero said:

Yup, I was. Each output to a resistor then all tied in to the speaker +.

Why would there be current to the speaker when it's not making a sound? If the 4 Schmitts aren't triggered to oscillate, wouldn't the current to the speaker be low, or 0?

When all 4017 outputs are low, the outputs of the 4 Schmitts are high. Therefore, they are driving current through the speaker.

The speaker only makes a sound when the current is CHANGING. Feel the cone when you apply power, you should feel it move forward or backward (depending on how the coil is wound) and it will remain in that position until the power is turned off or you start the tones.



Is there a difference between 1 uF and 68 K and 0.1 uF and 680 K? I mean, the math makes them equal, but is there a difference? Or just another way to do the same thing?
Yes that's right. But you will use a bit less energy since the resistor is higher. It is marginal. The other factor is that 0.1 uF is smaller & cheaper than 1 uF.

---------- Post added at 23:36 ---------- Previous post was at 22:21 ----------

I just finished assembling the circuit, and after connecting the sensor to the voltage comparator (LM393) and testing it, it works. 0.039v with the sensor pointed to the ceiling. 5.000v when I wave my hand over it. I have the sensitivity set to 0.4v, which is roughly 24" (60cm) away from the sensor.

I then made all the connections for the 74HC14. Double checked it. Applied power. The sound comes out fast and quiet when I wave my hand over the sensor. It sounds like it's oscillating quickly between both frequencies, even when I hold my hand over it, and it's real quiet. I checked the voltage on the output of the voltage comparator and it will only climb to 0.893v when I put my hand over it. I assume it's this too low voltage that's making the Schmitt not function properly. Yes, the Schmitt needs about 3 Volt to trigger and then about 1 Volt to "untrigger".

Why would the voltage comparator not be putting out the full 5v? and how can I convince it to do its job properly? If I understand what you said above, the comparitor works properly when the Schmitt is not connected, but can only rise to 0.893 V when the Schmitt is connected.

If so, then this means that something is loading the output of the comparitor. What happens if you unplug the Schmitt IC and leave everything else unchanged?

On my breadboard, I have my battery connected to the Input pin of the LM7805. The Gnd goes to the Gnd rail of the breadboard. The 5v Output goes to A) the resistor/pot combo for the comparator (the - Input on pin 6), B) the Vcc of the LM393 Comparator and C) a 10K pullup resistor to the output of the Comparator. This looks right so far, but you have not mentioned Vcc to the Schmitt.

Additionally, the Comparator has pin 4 connected to Gnd. Pin 5 is my sensor (the + input). Pin 7, the output, is to the Power rail of the breadboard. The Vcc and Gnd connections for the oscillator are off the power rails on the breadboard. Ah, I take back what I said above. However, do you mean that the Schmitt Vcc is connected to 5 Volt?

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However, do you mean that the Schmitt Vcc is connected to 5 Volt?

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Kolero said:

Here are the results of my tests:

If I physically remove the Schmitt, leaving all the connections, the comparator climbs to 4.998 volts when I move my hand in front of the sensor. So what ever was loading it has been disconnected.

BTW, 4.998 Volt is near enough to 5 Volt, so I would just refer to it as 5 Volt.

Assuming the comparator puts out 5 volts, yes the Schmitt is connected to 5 volts. The comparator feeds the power rail on the breadboard, and the Schmitt Vcc is connected to that.

By "power rail" I assume the 5 Volt line. Is this correct?

Leaving the Sensor and voltage comparator attached, and disconnecting the Schmitt Vcc pin 14 from the power rail, I get about 1.5 v from the comparator when I move my hand in front of the sensor. I also get a noise coming out of the speaker when I put my hand over the sensor. (more on the noise below) You said in your earlier post, that you measured 0.893 Volt at the comparitor output with the circuit as it is in my diagram. So by disconnecting Vcc to the Schmitt, the voltage has increased by about 0.6 Volt.

Leaving Pin 14 disconnected and then disconnecting the 220 ohm resistor from power (the one that goes to D1), I still get 1.5 volts when putting my hand over the sensor, and noise.

Therefore, the mysterious load is not going via the 220 Ohm.

Reconnecting the 220 ohm resistor, and disconnecting the jumper from the power rail to A, the comparator climbs steadily to 4.998 volts when I put my hand over the sensor.

By "power rail" I assume that you still mean the 5 Volt line. I did not know that you had connected A to the 5 V.

Is that where the problem is? Having A connected to the 5 volt output of the comparator?

The pot is connected to the - input of the comparator.

If bypass the comparator by removing the comparator output from the power rail, and feed 5 volts to the power rail straight out of the 7805, I get a louder (and I think higher pitched) version of the noise I get with the comparator in place.
I'm still confused by "power rail". The comparitor output is connected to the 10k resistor and to A.

The noise sounds like, and I can't confirm this, my two notes (E and G#) playing one after the other continuously and very fast. I just know that it doesn't sound like a single tone.

The Schmitt Vcc is receiving 5 volts at this point, but still isn't operating as it should.

See below.

I'm aware of the dangers of static electricity and I take the precautions I can. We generally don't get much, if any, static electricity in my house. The weather outside is damp, not dry, these days. But I also try not to handle the ICs because I'm paranoid. I use an IC puller to pull them out and put them in place.

I swapped out the 74HC14 for a second one I bought at the same time and I get the same results. I could try putting a capacitor and resistor on each gate to test them individually, but I don't think that's the problem.

I hope this helps your long distance trouble shooting and if there's anything else I can test, let me know. I have a multimeter, but no scope.

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By "power rail" I assume that you still mean the 5 Volt line. I did not know that you had connected A to the 5 V.

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Kolero said:

By "Power Rail" I mean the + and - lines on the sides of the breadboard (or protoboard). The - is connected to the Gnd of the battery. The + is the output of voltage comparator.
The Vcc {pin 8} of the comparitor should be connected to the +5 Volt rail, and pin 4 to the Gnd rail.

Pin 14 of the Schmitt should be connected to the +5 Volt rail also and pin 7 to the Gnd rail.
Using long jumpers, I'm joining the + on the left and right sides together, as well as, separately, the - on the left and right sides. The connections run the full length of the board as well (they aren't broken in the middle like some breadboards I've seen). I just checked Wikipedia and what I call the "Power Rails" are the "Bus Strips", for Ground and Supply Voltage.


A is connected to the output of the voltage comparator. Correct.

In this case, because the output of the comparator is connected to the + side of the Bus Strip, it should be receiving 5 V. The only time the + side of the Bus strip has power is when the comparator detects more than 0.4v. That means that pin 14 of the Schmitt and "A" don't receive power.

This is your problem.

My 9V battery is connected to the Gnd Bus Strip, and the input of the 7805. The 7805 has the Gnd connected to the Gnd Bus Strip, and the output connected to the voltage comparator Vcc, and through the resistor and pot to the - input. The output of the comparator is to the Supply Bus Strip.

I will try giving the Schmitt Vcc +5 V directly (and not switched on from the comparator), then take the comparator output directly to A instead of through the Bus Strip. Maybe that's the problem?

yes!

Thank you for your patience

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Kolero said:

Okay, my new setup is:

External power (9 v battery, or 12 v wall wart) going to 7805 + input, ground to ground bus strip. 5 v output from 7805 going to Bus Strip +.

That provides 5v power to all the components: Sensor, LM393, and 74HC14, and they now have constant power

The rest of the circuit is assembled as it should be. I think.

When I have the circuit assembled as per the diagram, I get a constant low note from the speaker, like a putt-putt-putt-putt of a race car engine. This sounds like what is called "motor boating"

It is usually due to positive feedback via the supply line.

Do you have capacitors on both sides of the Voltage Regulator?

The comparator is putting out 0.05 volts. Wave my hand over the sensor, the comparator puts out 5 volts, I get the high note, remove my hand and it's back to the putt-putt-putt. The high note is not a clean note, either. It pulses, or is on and off very quickly. Like a fast doo-doo-doo-doo

If I remove the 10k pullup resistor, I no longer get the putt-putt-putt sound. The comparator is putting out 0.025 volt. I put my hand in front of the sensor, the comparator puts out 2.3 volts, the pulsing high note plays, I remove my hand and a pulsing low note plays for a second and stops.

I thought the problem with the pulsing notes might be because the Schmitt isn't getting a full 5v from the comparator, so I connected A directly to the 5 v bus strip. I get the pulsing high note. I remove A from the 5v bus strip and I get a pulsing low note for about a second and it stops.

I'm also getting about 2.5 volt from H when the tone is making noise.
I presume that your multimeter is reading the average voltage of the square wave signal. The duty cycle will be about 50% and the signal is switching between 0 Volt and 5 Volt, therefore the average is about 2.5 Volt.

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Kolero said:

I didn't have bypass capacitors, but I do now. My supply is limited, so I put a 0.1uF from the Input of the LM7805 to Gnd, and another from the Output to Gnd. I also used 0.1 uF capacitors from the Vcc pin to Gnd on the LM393 and 74HC14 (I used the Bus Strip for the Gnd connections, btw). I think that's what you mean for a high frequency bypass?

Yes

I noticed in the datasheet that a 0.33uF capacitor is used on the Input of the 7805. The closest I have to that is a 0.22uF, so I tried that and no difference.

Do you have another 0.1 uF? If so connect it in parallel with the 0,22. That wil;l; give you about 0.32 uF which will be near enough.

I still get the motor boating with the pullup resistor in place, and with or without the resistor the high tone still .. well, I guess it still motorboats, too, just at a higher frequency. See below.

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