## Step 3: Sine Wave Frequency Detection

Next I measured the period of an incoming sine wave, calculated the frequency, and printed the frequency.  To do this I set up a timer in the ADC interrupt that increments each time the interrupt executes (a rate of 38462Hz).  Each time the incoming signal crosses 2.5V with a rising slope I sent the current value of the timer to a variable called "period" and reset the timer to 0.  That code is reproduced below (all takes place within the ADC interrupt).

prevData = newData;//store previous value
newData = ADCH;//get value from A0
if (prevData < 127 && newData >= 127){//if increasing and crossing midpoint
period = timer;//get period from current timer value
timer = 0;//reset timer
}

timer++;//increment timer

Then in the main loop() function, I calculated the frequency by dividing the timer rate by the period.  I used Serial.print to print these results in the Arduino serial monitor.

frequency = 38462/period;//timer rate/period
//print results
Serial.print(frequency);
Serial.println(" hz");

Fig 1 shows the signal coming into A0.  The start and end of one cycle measured by timer is indicated by the image note.  Fig 2 shows the output from the serial monitor (command/ctrl+shift+m).  This technique works great for sine waves, but when wave become more complicated (and cross 2.5V more than twice in one cycle) this technique breaks down.

```//sine wave freq detection with 38.5kHz sampling rate and interrupts
//by Amanda Ghassaei
//https://www.instructables.com/id/Arduino-Frequency-Detection/
//July 2012

/*
* This program is free software; you can redistribute it and/or modify
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
*/

//clipping indicator variables
boolean clipping = 0;

//data storage variables
byte newData = 0;
byte prevData = 0;

//freq variables
unsigned int timer = 0;//counts period of wave
unsigned int period;
int frequency;

void setup(){

Serial.begin(9600);

pinMode(13,OUTPUT);//led indicator pin

cli();//diable interrupts

//set up continuous sampling of analog pin 0

ADMUX |= (1 << REFS0); //set reference voltage

sei();//enable interrupts
}

prevData = newData;//store previous value
newData = ADCH;//get value from A0
if (prevData < 127 && newData >=127){//if increasing and crossing midpoint
period = timer;//get period
timer = 0;//reset timer
}

if (newData == 0 || newData == 1023){//if clipping
PORTB |= B00100000;//set pin 13 high- turn on clipping indicator led
clipping = 1;//currently clipping
}

timer++;//increment timer at rate of 38.5kHz
}

void loop(){
if (clipping){//if currently clipping
PORTB &= B11011111;//turn off clippng indicator led
clipping = 0;
}

frequency = 38462/period;//timer rate/period
//print results
Serial.print(frequency);
Serial.println(" hz");

delay(100);
}

```
<p>hello mam . im fascinated by your code. mam im currently doing a design project that detects emergency vehicle by their siren frequency. do you think its possible with your codes as the foundation of it ? i really need some help with this </p>
<p>Thanks very much &quot;uh-man-duh&quot;. I have been able to figure the issue out and it works well for my microphone circuit. Also thanks for making me understand interrupts better.</p>
<p>Hello Amanda,</p><p>Thank you very much for this very informative post!!!</p><p>I am currently working on a pitch controlled LED Christmas light and I'm using your code for the pitch detection, I'm using my own circuit, electret mic config and I am reading &quot;inf hz&quot; which means period is &quot;0&quot; but when i hold the lead alone that is connected to the a0 it reads some frequencies. I printed the &quot;period&quot; and it shows &quot;0&quot; confirming it.</p><p>Any ideas as to why period is 0?</p>
<p>Edit: I think I found out why, the input values I get are not &quot;slopey&quot; enough as they don't have a wide enough margin apart from the max and min values.</p>
<p>Thanks for the project!</p><p>I have constructed the audio input circuit outlined in the link at the top of this page. I'm trying to construct a device that would only light the Led attached to the Uno when a specific frequency is detected by the microphone. I'm having trouble develop code for this task and need a little guidance. </p><p>If anyone can help that will be great,</p><p>thanks!</p><p>-Alex</p>
<p>Thanks for the great project info. I've tried it out using an electret microphone with an amplifier, but I'm not getting a clean output on the serial monitor. Basically, the frequencies it spits out are all over the map. For instance, if I play it a note around 70Hz (I'm planning on putting it on my upright bass, so I've been using that to test) it will give me a bunch of frequencies that could be from 10Hz to 7000Hz, then give me several in a row that are about 70Hz, then back to all over, etc. Even when I played a 440Hz note from a tuner it gave me a decent amount of randomness. <br><br>My guess is that I need to adjust the slopeTol and timerTol values, since the random frequencies are often (though often not) some multiple of the one I'm looking for, making me think that it's missing some crossings. Am I thinking right? I don't really know which one to change and by how much; I've messed with them both and they're currently at slopeTol = 2 and timerTol = 15. Any ideas on some ballpark ranges for these if I'm looking to measure tones from my bass? Is there some other part that I should tweak? Thanks for the help. I'd really like to use your method instead of FFT or FHT, since it seems much more efficient for my project.</p>
<p>See post above.</p>
<p>One thing I thought of: right now I'm powering the Arduino through the USB, since I'm using the serial monitor to debug. Would using the USB as a power source be adding noise to the signal? My project will be powered by a 9V battery and I have one hooked up now, just turned off. Would it help to have the 9V source on in addition to being plugged in to the USB? I have to keep it plugged in to use the serial monitor, but if that's what's causing the problems...</p>
<p>Hi!<br>Thanks a lot for this!<br><br>although I have a question: Id like the Arduino to recognize some of the notes I play with my clarinet (so live sound), how is it possible to do this without having to use a digital track?</p>
<p>It's possible to do this with just the circuit and code.</p><p>I am using a variation of this sketch to read the output of a guitar pickup and display the string's frequency and intonation (an adjustment that corrects harmonics).</p><p>Since we are using instruments; we do have to consider some adverse effects of harmonics/overtones. I have included a Low Pass Filter ( 4.7K and 6.8uF - canning everything above 5kHz.) You'll want a filter that allows your highest note to come through - assuming you don't overblow or play using harmonics.</p><p>Double your highest playable note, then convert it to a frequency - insert an if statement to not display everything above it.</p><p><a href="http://www.phy.mtu.edu/~suits/etvsmean.html" rel="nofollow">http://www.phy.mtu.edu/~suits/etvsmean.html</a></p><p>Change the code to divide any sampled frequency to a fundamental listed.</p><p>A 10uF coupling capacitor did not work well with this circuit for my intended application. A value of 4.7uF instead allowed me to have a quite fluid readout in my terminal display. I have also removed the 47nF capacitor to ground. All it did was hold onto my sample for too long and prevent accurate/reliable readings.</p><p>I am in the process of writing a header for musical computations which includes FHT/FFT algorithms - but all you'll need to do is use your preferred method of identifying and dealing with different number values.</p><p>double noteFrequency = 440; // Concert 'A' - 440 hz</p><p>double deviation = 4; // nobody's perfect</p><p>double hiRange, loRange;</p><p>hiRange = noteFrequency + deviation;</p><p>loRange = noteFrequency - deviation;</p><p>if(frequency &gt;= loRange &amp;&amp; frequency &lt;= hiRange)</p><p>{</p><p>// We have detected roughly an 'A - 440hz&quot; do something</p><p>}</p><p>Expand this as you will but it's a basic start.</p><p>Thanks for an excellent instructable Amanda!</p>
<p>Aside from inventing an analog computer or using quantum computing, the computing devices we all use know 1's and 0's. Using a digital signal, 10-bit is referring to 2^10=1024, that is with ten on/off switches, there are 1024 combinations. That is why there are steps to the wave. </p><p>The sound that we hear is the intensity over time, how loud a sound is doesn't tell us what note it was. FFT is a 'transform' to show to intensity over frequency, then when we see intensity at a certain frequency/note we see that note was played. </p><p>I've seen libraries using the Teensy microcontroller running at 120MHz being able to sample and do a FFT to determine notes. Start looking there. The only way I could think of it being possible otherwise, is if it was a small pattern of exact notes you may be able to do it using set very specific set of bandpass filters, but that approach would have other problems.</p>
<p>I'm working on a personal project about audio frequency detection using Arduino. I have a question to ask you about why the last frequency detected by the software it's repeated in the serial monitor.</p><p>I mean, while I playing a sound and then I have no signal in the line, however, the serial monitor still printing the last frequency detected. Do you know how to fix that or if it is possible? I leave an attached screenshot to show you what I'm talking about.</p><p>Thanks</p>
<p>thank you for this</p>
<p>Thanks a lot for posting this very clear and helpful project. <br>I build it but using the soundcard output of a computer(or a similar one, like a phone or mediaplayer) as an input. Since these signals are much stronger I left out the opamp. For the rest the setup is similar: one resistor(+) and a potmeter (-) as a voltage divider before the 10uF Cap and two resistors (+&amp;-) as a voltage divider on the other side. And the 47nF Capacitor between signal and (-).<br>It works fairly good but the readings show inconsistencies f.i.: many lines of an almost perfect 80,80-82,01Hz and all of a sudden a 25,94Hz (and strikingly often half the values of the signal) or say a 12820,67Hz passing by. And often similar erratic glitches pop up at the beginning and/or at the end of a signal.<br>For an artwork I want to steer a servo with this technique, with something moving in sinc with a video (either directly (frequency is position) or through a ssc32 (frequency is position and signallength is speed) with charstrings passed over). Therefor these jumps are quite annoying. I tried tweaking a lot with the settings in your program (ampThreshold, timingTol, slopeTol) and on the hardwareside with capacitors to get the ripples out but so far with no luck. Any suggestions?</p><p>My iduino is powered by the computer to be able to read the readings, and I don't have an oscilloscope to check the signal-output of the computer. I tried other sources though, with similar outcome.</p><p>Many thanks anyway for the instructable which already helped me a lot and many thanks in advance.</p><p>Matthijs</p><p>ps:<br>steering servos this way seems a kind of a detour but manually putting the right blocksignals in the right place and play them with the mediaplayer appeared to be even more work. Using the frequency technique makes it far more flexible and ubiquitous. </p>
<p>Thank you for your sharing Amanda!! I don't have to start from the zero point on my automatic guitar tuner project!</p><p>But I have a question.Can I use a piezo to pick up the vibration or the sound instead of using a mic,which enables the tuner to work in noisy environment?</p>
<p>Yes you can. Im using it on a violin. At the moment the algorithm is a little sporadic but if you turn down the time and slope tolerances it works a little better. I think if you restructure the code to get the full 10 bit resolution instead of 8 bits, you should be able to make this code work better. But the extra instruction cycles might hinder any other operations... </p>
<p>I've got a project along these lines as well, and I wondered that same thing about picking up noise from other sources (or instruments, since I plan on using it while playing). Using a piezo came to mind, glad to see someone has done it successfully. I was wondering, what did you use to stick your piezo on your instrument? I don't want do anything that would damage the wood. Did you use some sort of adhesive that's safe for string instruments?</p>
<p>I tried a under the bridge pick up, as well as a bridge stick on pickup; A generic rod piezo and a Shadow SH 3001 respectively. I used it on a dedicated electric so the rod piezo was appropriate and much cheaper, but there are film-type under the bridge pickups like Realist pickups that should work for you. I have found that blending both types of pickups (horizontal and veritcal) through a cheap behringer micromix mx400 gives really good results, although you'll have to contend with two wires instead of just one. </p>
<p>Gotcha, thanks. I'll see if I can find something like that for my upright bass. I'm planning on using it to control an LED strip, so I probably don't need the quality to be quite that high; one pickup should do it. Did you need to wire it up with the whole op amp setup from the Audio Input tutorial, or do some have amplifiers built in?</p>
<p>Yes, you'll need to amplify it a little bit based upon the voltage response characteristics of the element you are using. You'll have to tinker because no two piezo's are the same. There are a lot of projects for arduino out there on how to do this, just search &quot;arduino audio input&quot; if the above schematic isn't descriptive enough for you.</p>
<p>So with this arduino code I would be able to control a the light's frequency with the frequency of the sound? I want to build a lighting system for my room and car that will react with the sound, but in a way so that bass=&quot;cool colors&quot;, treble= &quot;warm colors&quot;(or even vice versa). I feel like that would give a better experience to the music</p>
<p>Did you manage to get your idea working? I have a similar project idea.</p>
<p>Hi Amanda,</p><p>Thanks for the very usefull work you have done, nou I can measure the frquency from my agriculture application that use a exciter ring.</p><p>I have one qustion how can I change to another analog pin in the ide?</p><p>Thanks,</p><p>Rien Brand</p><p>Netherlands</p>
<p>We did it, finally facing problems. We used electric guitar for this purpose. Thanku Amanda. Keep up the good work !</p>
<p>Hello Amanda thanks for your sharing. i want to ask about this one..<br>so i am developing an Arduino human scream detection is it possible to me detect human help scream voice using this kind of Arduino program? because i want to build up the component consist by band pass filter , gain, and rectifier circuit and then look for its pitch detection and voice duration..<br><br>Do you have any idea about the circuit that i`ll need to complete my project?<br>Or is it possible enough to use some Arduino library and write the speech recognition code?</p>
<p>Hi Amanda, thank you very much for this source!! very amazing!!!</p><p>but... little problem my arduino...</p><p>your source is exellent !!</p><p>but.. my arduino is not working </p><p>my arduino version...is...</p><p>8-bit<br>Microcontroller<br>with 256K Bytes<br>In-System<br>Programmable<br>Flash</p><p>maybe...</p><p>version is problem is different???</p>
<p>Hi Amanda, thank you very much for this instructable! Very useful!</p><p>I prefer this simpler code version (integrated with amp treshold), because I want to make a sound analyzer , where you whistle or sing a &quot;oooh&quot; note and then you have the frequency. Making a portable built with a 4 digit display and there it is a perfect gadget for any sound engineer or musician, who wants to know which frequency causes microphones feedbacks.</p><p>Does it make any sense collecting a number of measurements and make a mathematical average? as I don't need a fast process, but a slower and more solid (without &quot;garbage&quot; measurements); I tried some &quot;for&quot; cycle with a simple array, but it doesn't seem to add any precision (maybe I don't know where to put it).. </p>
Hi amanda...your instructables on arduino are great..however i want to know if it is possible to measure a amplitude of sine wave on arduino
<p>Thanks for the instruction! I just put together a circuit with an amplified electret mic signal using opamp feeding into it. However, when I'm looking at the serial output, it only seems to work for the first second or 2, then it stops working with the last line looks like attached image. Any idea what could be the cause? thanks!</p>
<p>Hi, this is an excellent project. It works fine on my arduino uno. However, I need it to run on a arduino mega with ethernet shield. When adding the codes to my ethernet project, the connection to internet is brocken (I'm uploading data onto xively server). Any suggestion?</p>
Hiii<br>How we meaured the frequency ....I want to detect frequncy range 60Hz to 100Hz....can I use this progtame thanks and quick reply from you
<p>This is awesome! I'm looking in to a guitar-MIDI pedal, but a DIY solution is cheaper and way cooler. Props to you for this awesome bit of code!</p>
<p>Hi, has anybody completed this project (possibly, with a diff sort of mic) and wouldn't mind sharing about it? Am a beginner and would really like to try this so.. slightly more detailed steps would be most helpful :D</p>
<p>Hi amanda, i want to congratulate with you on this instructable, really powerful :D I have a question, that is is it possible to check the frequencies of a playing song in this way, through an aux signal from i.e. an MP3 player or the notebook audio headphones output (after the right managment of the signal like in your instructable on arduino auido input)?</p><p>Thanks a lot</p><p>;D</p>
<p>Has anyone made this project with ChipKit Uno32. I am really looking for projects like that for my Uno32 developement board because I need to read analog signal frequency coming from optical rotation sensor.</p>
Great work! I'm trying to use this code for an automatic laser oscilloscope I am designing. <br> <br>I've found that the code stops measuring frequencies as soon as I try analogRead() from a different analog pin. At the moment I don't fully understand the lower level programming of the ADC that you've done. Is there any way to read from the other analog pins without interfering with the pitch measurement?
yes, the way this is set up, all of the other analog pins are deactivated. you can read an analog value from a digital pin by using RCTime: <br />http://arduino.cc/en/Tutorial/RCtime <br />https://www.instructables.com/id/Arduino-Basics-RCtime/ <br />hope that works for what you're doing.
<p>Thank you for the great article. I was just wondering can I use a microphone with a preamp to make the detection.</p><p>I have :</p><p><a href="http://www.freetronics.com/products/microphone-sound-input-module" rel="nofollow">http://www.freetronics.com/products/microphone-sou...</a></p><p>Thank you very much!</p>
<p>i tried to build guitar tuner <a href="https://www.instructables.com/id/Arduino-Guitar-Tuner/?ALLSTEPS" rel="nofollow">https://www.instructables.com/id/Arduino-Guitar-Tun...</a></p><p>but arduino can't read the input from my guitar.<br>can you help me to solve this problem ?</p>
do you have an oscilloscope?
<p>i don't have oscilloscope.<br>does become a problem if I use 100nF Cap on the DC offset ?</p><p>i see your project use 47nF Cap.<br></p>
<p>no that should be fine. You will need an oscilloscope to debug this, maybe see if there's a <a target="_blank" href="http://hackerspaces.org/wiki/List_of_Hacker_Spaces">hackerspace</a> or school near you where you can use one for free.</p>
<p>what is the main problem that the input from guitar can not reach the Arduino?<br><br>whether the project could be completed if there is oscilloscope ?</p>
<p>you could try using a computer running audacity as a makeshift oscilloscope, to find out where the signal is getting lost. Do you have an audio input on your computer?</p>
<p>yes, i have.<br>how to make audio output from amplifier and DC offset circuit into my computer ? there are 3 outputs &quot;A0 , 5v and GND&quot;</p>
<p>I'm new in Arduino, I want to make this but with an Electret Microphone, I think it's very different than the microphone you used. How can I make the circuit with an Electret Microphone?</p>
<p>it shouldn't be too different, but you might need to change the gain on the amplifier going into the Arduino's analog pin. You will probably want an oscilloscope handy so you can see what you're doing.</p>
<p> Do you know if there's a virtual oscilloscope which I could use? Like a PC program. </p><p> About the microphone, I'm using an Elecret Microphone with Breakout Board (amplifier included), I connect it directly to the Arduino, is everything alright?</p>
<p>i guess you could use the audio input on your comp and record using Audacity or something.</p>