So, first off.

This instructable was a LONG time coming. I had come up with this idea a while ago, after hearing about the details behind some basic "speech jamming" anomalies that occur when people use intercom systems. Basically, the intercom would introduce an ever so slight delay to the output of the speaker, so you would end up hearing an echo. I had planned on making this many months ago, as I previously stated but I was going to try and go discrete, aka, use a micro-controller and attempt to program some sort of delay code. But alas, I never could figure it out.

Then I found out about a very, very neat little IC, the PT2399. This thing is the heart of this circuit, and is actually pretty impressive considering the pricing.

This echo is typically within the range of 30 ms - 300 ms, and it varies a bit. But, what happens when this delayed speech hits your ears?

You have a tendency to start stumbling over your words, and you more or less, just lose your train of thought. I'm thinking this may be due to the way your brain processes your words; since there's an inherent "delay" that your mind creates, it somehow interferes with your speech processing center.

It's a pretty funny thing to play with and show people the effects of. However it's not foolproof; if you concentrate hard enough, and speak slowly you can overcome the effects of the jammer. It's still amusing to see your friends think "oh, this'll be easy!" and then proceed to have the speech capability of a 2-year-old.

The circuit itself is quite simple, too. Only three "active" components, the 5 volt regulator, the PT2399, which controls the delay, and the LM386 which amplifies the audio from the PT2399. And, if you go with the improved version, a KA358.

Step 1: Material List

"Solder is key"



Soldering Iron (a given)

Solder (also a given)

Wire (pretty sure this is a given, any thin gauge wire should work)

Protoboard, or breadboard (whichever. I always use protoboard because it's more permanent)

Headset (this is both your output and input, since it works only with a headset on)

1x PT2399 (this is the delay chip)

1x SPST switch

1x LM386 (amplifies the delayed audio coming from the PT2399)

1x 7805 regulator (everything on this board will use +5 volts)

1x 9 volt battery clip (this is powered off of a 9 volt battery)

2x 3.5 mm audio jacks (or you can solder your microphone/speaker directly on, your choice)

3x 47 uF electrolytic capacitors

2x 20 k potentiometers

4x 0.1 uF capacitors

1x 0.01 uF capacitor

2x 470 pF capacitors

4x 15k ohm resistors (1/4 watt)

2x 10k ohm resistors (1/4 watt)

1x 2.2k ohm resistor (1/4 watt)

2x 220 uF electrolytic capacitor (non critical value, anything above 100 uF should work)

2x 1k ohm resistors (1/4 watt)

1x LED (whatever color you want)


For improved sensitivity and clarity:

1x KA358 or equivalent (if using equivalent make sure you're using a single supply capable op amp!!!)

1x additional 20K potentiometer

2x additional 1k resistors

1x additional 10k resistor

You can get all of these things from eBay, mouser, wherever you source your electronics components. The PT2399 isn't expensive, either, about $1 each!

Step 2: Follow the Schematic.

"This is my work face"


I put this schematic together using ExpressSCH. A great program, and 1000 billion times easier to use than paint.

Some notes:

Nothing on here needs a heatsink. There's very little heat dissipated by this circuit.

The second schematic version is for improved sound clarity. The potentiometer adjusts how sensitive the microphone pickup is.

I would also deeply recommend you mount this circuit onto something or put it in a project box. The PT2399 is a CMOS IC, and is very sensitive to static electricity, along with the fact that your fingers will easily introduce noise into the circuit. A small flat piece of wood just hotglued to it would work too, plus it looks a lot nicer than just a floppy circuit hanging out in the wind.

Jared I need help putting this together! Assist me!

It can help, if you're having problems putting it together to print out the circuit diagram and scribble over components you've already soldered on. You can also try labeling each part by number, along with the previous technique to really make sure you put it together correctly. And for the semiconductory bits, pulling up the datasheets for each part can help identify the orientation for them so you don't accidentally put them in backwards.

Here's the sheets for your convenience!




For the improved version...


Step 3: Video for Proof of Concept

"This is my 'I'm proud of what I've done' face"


The potentiometer connected to the PT2399 adjusts the delay amount, and the potentiometer closest to the LM386 adjusts the volume output to the headset. The video shows just how well it works, even when pretty poorly tuned!

Step 4: Some Thoughts...


-Jared after his eardrums were punctured by a sound related accident-

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

This circuit IS the first iteration and as such it does have a few small problems which can be easily fixed.


The output of the circuit is noisy

This can be easily attributed to any number of different things. The PT2399 is "an echo audio processor IC utilizing CMOS technology which is equipped with ADC and DAC, high sampling frequency, and an internal memory of 44k."

It claims to boast a THD of under 0.5%, however this distortion relies heavily on the amount of delay you ask of the IC. The more delay, the more pronounced the distortion is in the output.

Another potential reason for this is the fact that we're using a microphone directly to the PT2399. Microphones are inherently small signal sources. A way to combat this would be to introduce another amplifier between the microphone and the PT2399. I attempted to do this, actually but I believe the op amps I have are broken/fried due to a previous project of mine going south. Figures, right? Turns out, that I completely overlooked the fact that microphones are inherently true AC output devices. Since there's no negative supply, the op amp isn't capable of really doing anything with the microphone's input, so adding some DC bias fixed the problem and I've added a new schematic to the instructable as such!

Any simple pre-amp circuit should work for this just fine.


I'm not getting any problems with my speech, what gives?

You actually need to "tune" the circuit a little bit before it'll give you the delay you're wanting. It'll be a very subtle delay, almost nonexistent but still apparent. Once you have it tuned properly, and with enough volume coming into your ears you'll be talking like a child in no time!


Jared I would like a PCB for this, please help!

For once I'm actually ahead of you!


Above link is a zip folder containing the PCB file (it's an eagleCAD file) and the passives part list. I recommend using OSHpark, their PCB quality is amazing.


Jared I want to do this to an entire room of people!

Well. You can do what I did, which was add another stereo jack to the circuit. It'll connect directly to the output of the PT2399, basically in between the LM386 and the PT2399. This'll let you hook it up to a stereo receiver easily, although feedback may be a huge problem.

However, I'm not 100% sure how well it will work with this method. You'll have to try it yourself!


^^^^^^^^SAFETY DISCLAIMER^^^^^^^^

Also, please be careful with this when first testing it, especially with a headset. Due to noise and other unforeseeable problems with how you've put the circuit together it may make horrible noises and other various sounds of electronic distress RIGHT into your poor, now punctured eardrums. Be safe, and have the volume down as low as possible, or even better, use a speaker that's not an inch from your ears!


One more little thing...

And, thank you for taking the time to read through this fully and, hopefully, give a try at making one of these. If you enjoyed and liked how I did this instructable please take a moment to click the vote button up top for the audio contest, I'd greatly appreciate it!

<p>Great circuit, I'm using it as my project for my college circuits class. I built the improved version and got the diode to light up which made me think that it was working fine, but when I hooked up my headphones to it, I didn't hear any sound. Does this have to do with the type of headphones I used? I didn't have a splitter so I just used two different headphones, one for the mic, one as the actual headphones. </p><p>Any help would be appreciated! </p>
<p>Did you end up solving your problem? I want to build this but not sure if it will work haha</p>
<p>Hai . Im nazarul from malaysia . Can i ask your team help on how to develop the simple diy jammer . For blocking only 3g or 4g frequency and just allow gsm running in around 5 to 10 min . Im taking final year project . And im doing this for study purpose . Unfntly, this country still lack on these jammer knowledge . Perhaps your team able to teach me a little bit how to develop it . And the medium that can be used . Bcause i cant find any other way to do this project . Thanks you</p>
<p>You have made what could be considered really freaking close to the cure for stuttering. That's right, there's a cure for stuttering. It turns out that when people with chronic and severe stuttering, all the way down the spectrum to persons with minor stutter issues, that if the subject wears a mic and headphones, feeding their own mic signal through the headphones, BINGO- no stutter. Gone. 100% of the time. From what I read, it was more or less a lab accident. The delay is what has to be right. The delay between when the person ends a word and when the subject hears the end of that word, via the headphones, a millisecond later. I bet if you got the delay right, packaged this up real slick, possibly with a second use for the main unit, like cell power backup, or bluetooth... with some modern &amp; youth friendly headphone / mic options, and threw it on kickstarter, you'd be making tens of thousands of them in no time. After wearing the device for a period of time - everyone is different - the subject is stutter free. </p>
<p>Thank you for the amazing suggestion Pete. Unfortunately, though the IC that I used for this circuit can only go down to about 38 ms of delay, however I researched more and found one that could do anywhere between 0.5 ms of delay and higher. The only drawback is though is that it's a more uncommon chip and I'd have to buy it from China via aliexpress. Still though, I'll keep this in mind.</p>
<p>Nothing wrong with Aliexpress. (They have some neat diy 38 led light bulb kits for $1.54). Great prices. I remember one time, calling back to the States from overseas and having that terrible echo. For some reason, I couldn't stop laughing, which only made matters worse - all that laughter coming back at me! :-)</p>
<p>I'm wondering if you are about the same age as I am and reading psych articles about the same time? I remember wanting to do the same thing after reading an article about curing stuttering (it was about 30yrs ago perhaps?) :) Great job.</p>
You look like Austin powers
<p>Can I use electret microphones ?<br>I cant seem to understand the schematic , there are some triangles that aren't connected to anything , like the one below the speaker or pin 4 or 2 of LM 386 .<br>And I cant figure out which schematic is the newer one .<br>Sorry and thanks in advance .</p>
<p>The triangles in the schematic mean ground.</p><p>The schematic that has the KA358 addition is the newer one, and yes, you should be able to use and electret microphone with it. Just make sure you keep the bias resistor on the mic and it should work great.</p>
<p>thanks a lot.</p>
<p>I feel like pranksters in schools everywhere will be using these on the teacher in maths class... Not that I would ever do anything like that :P</p>
<p>My first thought was teachers using this on students that wont quit talking ... not that I would ever do something like that... ;-)</p><p>I had considered trying this last year, via arduino, when I had read about the research. Glad you found a better way, Jared. Thanks.</p>
<p>My first thought too. You could probably feed this through an iphone with an app like garage band to cut out feedback. Hook it up to a portable speaker while using a good unidirectional mic and go around jamming speech. There is a rather effective app on iphone that does this already though, but I always used it with headphones and never tried it with external speakers. </p>
Very cool!
<p>Its wonderful</p>
<p>Hmm, it doesn't have anything to do with a laser, but I voted anyway. :P</p>
What a novel idea! :)

About This Instructable




Bio: I'm 21, and I have a profound interest in electronics, lasers and Geology.
More by Inducktion:Speech Interruptor/Jammer Sorry I don't do work with bepis  
Add instructable to: