1V audio burst every OTHER pushbutton

[devin sheets]

Hello all!

I am trying to build a circuit which emits a 1V high frequency audio signal (maybe 10kHz?) for about 5ms every OTHER time a pushbutton is depressed. Can a 555 be configured in this way? Or what is the simplest, most inexpensive way to accomplish this? I am a complete beginner here, but I have been tasked with a very specific project and would greatly appreciate some help!

Thanks!!

 

[Les Jones]

Does the signal from the push button do anything else ? If it doesn't you could use a push on / push off button to generate a positive transition on every other press. If not you would first need a bistable to divide by two. you would use that signal to trigger one 555 configured as a 5 ms monostable. The output from this would then drive a second 555 configured as a 10Khz oscillator. The data sheet on the 555 should give you enough information to configure the 555s and calculate the values of the resistor and capacitors to set the timing.

Les.

 

[devin sheets]

Les, thanks for your reply! I am an absolute beginner here, hardly know what resistors and capacitors are, so I'll need a lot of spoon feeding! The application is that I need a small battery powered device which can somehow be placed on the sustain pedal mechanics of a piano which will send a 5ms 1V 10kHz tone every time the pedal is released after being played (when all the dampers come down on the strings to mute them). The device needs to be as cheap, simple and reliable as possible, and my first thought was a simple switch that the pedal triggers every time it moved up or down (i need the burst to be emitted at exactly the time when the pedal is nearly finishing its release movement back to a nominal position), and I was having trouble finding a switch that worked the way I needed it to (it needs to be very easy to trigger, and silent). So I figured a simple pushbutton would be better, but then I'd need to figure out a way to only capture data from it's every other depression. Does this clarify things?

 

[Les Jones]

Yes it somewhat contradicts your initial description. You need it to operate every time the button is released. Not every other time. You also want someone else to design it not just help for you to design it. The cheapest solution would be to use something like a PIC12f629 or ATtiny13 but to use that solution you would need the hardware and software to program them and someone to write the firmware. Using 2 555s (Or a single 556) would be most suitable for you to build.

Les.

 

[AnalogKid]

I think there is a more simple way, but first let's go back to the sustain pedal.

1. IF you want the sound burst every time the piano sustain pedal is released, then that is a switch, a 5 ms monostable, and a 10 kHz astable.
2. IF you want the sound burst on every other pedal release, then you need a toggle flipflop before the monostable.
You can not have both. Pick 1 or 2.

How accurate does the 10 kHz frequency need to be? Do you just want it high enough that most people won't hear it, or is it triggering some other device that requires an accurate frequency tone burst?

Separate from that, where does the 10 kHz audio signal go? Is there to be a speaker inside the box with the switch and circuit, or does the tone burst go over a cable to an audio amplifier and speaker somewhere else?

ak

 

[devin sheets]

Thanks AK,

#1 is correct, I need the burst every time the pedal is released. The reason I said "every other time" originally was in reference to a switch or button that the pedal triggered every time it moved up or down since there is a pedal depression, then a release. I assumed the switch or button would be triggered in both directions, so that's where the "every other time" comes in... I only want the burst on the release movement trigger, so the depression movement trigger would need to be ignored. Unless I can find a switch or button that can be triggered by the pedal movement in only one direction? But it would have to be a very easy trigger and very quiet, and the switches I found at Radio Shack are neither of those. The tone doesn't need to be super accurate, maybe within 1kHz? The tone goes into a pro audio mixer board and is used as the "key in" to trigger a compressor or ducker.

 

[Tony Stewart]

Some electric piano's use normally open pedals, so why add not use the damper signal to key in the ducker? instead of 10kHz.
I assume the ducker has settings for attack, decay, ratio and knee type and the damper pedal output can be split out.

If this is a real piano, switch threshold adjustment will be critical and must allow considerable overtravel with a flat spring bar. Silent switches of this type are easy to find from Grayhill.

 

[cowboybob]

Welcome to ETO, devin sheets!

If I'm understanding your query (and it sounds as though you're using a "regular", non-electric piano), a hall effect sensor (https://www.sparkfun.com/products/9312) could be used for the switching component. You could adjust the position of the sensor OR the magnet to achieve the desired trip point in the travel of the sustain pedal or its lever/rod to activate the tone circuit.

It would be used to apply power to your 2 OpAmp timer/oscillator circuit. A small downside would be continued current draw in the "ON" condition.

 

[AnalogKid]

The tone goes into a pro audio mixer board and is used as the "key in" to trigger a compressor or ducker.

How do the tone bursts get to the mix console? Through the air to one of the piano mics? Direct cable to a mic or line input?

If through the air, how do you keep the 10 kHz tone burst from interfering with the 3-4 kHz frequencies of the upper octave?

I had a way to do the whole project in one hex inverter, including the toggle flipflop. But the project definitely is easier without the ff.

ak

 

[audioguru]

How accurate does the 10 kHz frequency need to be? Do you just want it high enough that most people won't hear it?

Why do you think most people play with guns and therefore are deaf to ordinary sounds?
Maybe the piano is played on an AM radio station that can't "hear" 10kHz.

 

[devin sheets]

Wow thanks everyone for your responses! I generally have very little clue what is being said here (I have almost no experience in the world of electronics, I am a musician and sound engineer), and so I hope that someone might be willing to really spoonfeed me the steps involved in getting the parts and assembling whatever will work!

More details:

I am using a piano mic which has been designed to only pick up low frequencies (it will be blended in with other mics for the mid and high frequencies). On the mixer board, I will apply a low-pass filter to this mic, but I need to quickly reduce the signal level every time the pedal is released (it makes a slight thumping sound because all 88 dampers come slamming down on the strings to mute them). I figure that if I can use a "Y" patch cable right before the audio input on the mixer and sum together the mic and another signal containing a very loud 10kHz burst every time the pedal is released, I can use the compressor on the mixer board to act on itself pre-EQ, and I will set the threshold to above the maximum mic level, but below the burst level, and set it to last about 5ms. If the burst is 5ms long, and the compressor last for 5ms (attack of zero), the total compression time would be about 10ms which is the length of the thump on an oscilloscope.

So it seems my options here are to have a circuit design which sees a brief input voltage and outputs a brief 10kHz tone, or a circuit that outputs a brief 10kHz tone only when there is a voltage change from off to on. The first would require some kind of switch which can be flicked in either direction from a nominal position to which it returns, and the second would only require a simple push button. Yes?

 

[AnalogKid]

Why do you think most people play with guns and therefore are deaf to ordinary sounds?

I don't think that. I also don't think most people are psychotic.

 

[devin sheets]

I should also mention that the 10kHz tone might need to be volume adjustable, and also needs to be a clean on/off with no thumping or subharmonic artifacts of its own... would be nice as well to have an adjustable delay of up to 20ms or so but that part isn't super critical since the timing can also be adjusted by its physical location on the pedal mechanics I suppose. I really appreciate everyone's input here!

 

[AnalogKid]

So it is a direct cable connection at mic level from the tone burst generator to the mixer input. Yes?

ak

 

[devin sheets]

Yes it is technically a "mic" level input to the mixer, but I need the burst to be so far above the mic signal when combined (at least 30dB) that there is no confusing which is burst and which is mic. It would be nice to have a volume adjustment on the circuit so that I can set the output to approximately 30dB louder than whatever the mic gives me (I won't always be using the same mic, and some pianos are louder than others and the placement in the piano can affect the level as well...). I figured a max output of 1v would be more than enough play... mic level is way below that, but 1v of headroom would allow me to compensate for potential line level signals in the future if I move away from using a mic.

I'm sure there is some smart person here who could probably just tell me what parts to go buy and how to assemble the circuit. Or maybe what I'm asking for is super complex and expensive, I have no clue either way. I appreciate any help...

 

[devin sheets]

So basically, to sum it all up with some adjustments as I learn more about this on the fly,

I need to build a circuit which emits a 5ms 10kHz tone at an adjustable output voltage from 0-1.5V and has an adjustable delay from 0-100ms, triggered solely whenever a 9V battery input through a hall effect sensor drops from 9V (or any voltage?) to zero.

How does one go about designing such a thing??

 

[dougy83]

Yes, it's simple. Here's a schematic. Hall-effect sensor is the rectangle with a cross on the left. The gates are from a single CD4093 logic IC.

 

[devin sheets]

thanks, i have zero clue what that means, but i will try to figure it out! i really appreciate you taking the time to draw that up for me.

 

[audioguru]

A problem is that your compressor has an "attack time" from when it is given the 10kHz beep to when it actually cuts the 10kHz. So the 10kHz will be heard.
Another problem is that your lowpass filter is not perfect, it reduces the 10kHz and all other high frequency sounds from the piano, it does not stop it. So the 10kHz will be heard.

Therefore I think you should mute the thump with a mechanical, optical or magnetic switch.

Modern recordings even mute a singer's cough or sneeze! Can't you cut out the thumps from the recording?

EDIT: It might cause damage if you use a Y-cable which will inject the high level 10kHz into the microphone and overload the mic preamp. A separate input is needed on the mixer for the beep.

 

[devin sheets]

All valid concerns of course, so I tested this out already on my yamaha cl5 console and with an attack of zero on the compressor and a low-pass at 100Hz, the 10kHz tone can't be heard even when it is near clipping the mic pre.