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OscilloPhone: Use your Smartphone as an Oscilloscope / Signal Generator

by Loann BOUDIN | 2015

Oscilloscopes and Signal Generators are two essential electronics devices to create and test electronic circuits. Unfortunately, these devices are very expensives for students starting electronics, or makers who want use electronic circuits in their creations just once...

The idea of my project is to rethink your smartphone as a portable, powerful and secured platform, able to simulate an oscilloscope and a signal generator for your electronic circuits. Here, your phone isn't just an accessorize or an ordinairy remote control : it becomes the center of the project, and a tool to help you create better things in the future.

The OscilloPhone project includes:

  • an oscilloscope input for visualize electronic signals ranging from 150 Hz to 15kHz. Beyond this bandwidth, the displayed signals have a lower quality. Signals up to ±50V up can be injected on the input of the circuit. A warning LED alerts the user when a too high signal is measured.
  • a signal generator output, able to generate sinusoidal, square and triangular signals up to 15kHz. A potentiometer is used to adjust the signal amplitude.
  • a signal generator power output, able to generate sinusoidal, square and triangular signals up to 15kHz and 2A. A potentiometer is used to adjust the signal amplitude.

A part of this project is based on an electronic circuit invented by chipstein. I reused and improved his circuit to include it in my project.

When writing this tutorial, I wanted to provide excellent quality pictures to facilitate the making of my project. I retouched some photos to get a pure white background (see step 2) using the recent Antzy Carmasaic's Instructable: "Pure White Background Photography Using Smartphone"

Step 1: Why those electronic devices are so important?

Those devices are very important for an engineer on the go or any maker who wants to build electronic circuits. They are the only way to test that your electronic circuit operates as well as you want with electronic signals.


The Signal Generator :

"Signal generators, also known variously as function generators or waveform generators, are electronic devices that generate repeating or non-repeating electronic signals. They are generally used in designing, testing, troubleshooting and repairing electronic or electroacoustic devices." - definition of signal generator by Wikipedia

As the Wikipedia definition says, a signal generator is used to generate various electronic signals into electronic devices.
On the Signal Generator, you can choose the kind of signal you want (sine wave is the most common waveform but sawtooth, square and triangular waves are commonly available), his amplitude in volts or percent, and his frequency.


The Oscilloscope :

"An oscilloscope, previously called an oscillograph, is a type of electronic test instrument that allows observation of constantly varying signal voltages. Oscilloscopes are used to observe the change of an electrical signalled time." - definition of oscilloscope by Wikipedia

More famous than the signal generator, the oscilloscope can in effect allows observation of electrical signals over time. It's a kind of voltmeter for varying and non-varying signals with a screen for the visualization. On the oscilloscope screen, you can observe the form, the amplitude and the frequency of the signal studied.


How to use these devices :

Now that we know what these devices are and what they can do, how to use them?
Instead to try to explain this with a long and boring paragraph, I'll use an example of a circuit that need to be tested.
Let's test the circuit called "non-inverting amplifier" : here, this circuit must amplify twice the input voltage. To check if it operates correctly, a sine wave is generated on the circuit input with the signal generator. Then, the output signal of the circuit is connected to the oscilloscope, measured and displayed on the oscilloscope screen.
If the circuit operates correctly, the output signal shall be sinusoidal and has the same frequency as the input signal generated by the waveform generator. The output signal shall be amplified twice compared to the input.


Conclusion : for testing an electronic circuit, an electronic signal is generated on the circuit input by the signal generator. The output signal of the circuit is measured by the oscilloscope and if it meets the requirements, then the circuit operates correctly.
By this manipulation, we visualize the impact that the electronic circuit has on the input signals.

In the power supply circuit you used 33microfarad capacitors and while it the parts description you written 22microfarad. Which one to use? I am confused. <br>and to which pin of the lm324 ic ..the minus 8V nd ground supply is to connected?
Yes, I forget to update the components list after a little change in the schematic.. my bad<br><br>Choose the 33uf ones ! (always refer to the schematic)<br><br>For the LM324, connect the +8V to the pin 4 and the -8V to the pin 11
<p>Thanks Loann for this awesome project, I need it so bad ;)</p>
Did you have any base paper regarding this?
Why do we need 2 function generator output?
We don't &quot;need&quot; two function generators. It's just an option. If you want, you can just use one function generator.
Can you explain that naming the cable portion? Which cables are named and it is connected to where? Sorry if am really nagging you with lots of questions..i'm doing this as my final year project..thats why..<br><br><br>
<p>In my Instructable I tried to be the clearest possible in my explanations. I gave a lot of details (including the names of the wires in the electronic circuit), but this project is still a bit complex for an electronics beginner. I don't know if you're studying electronics, but I hope so: if not, this project could be too hard as a final year project. In addition, a final year project must include some researches, be fully understood, and must not be just a copy of an existing Instructable. Otherwise, where is the merit ?</p><p>I hope sincerely that you will be able to succeed your final year project, but maybe focus on my project is not a good idea.</p>
I'm improvising it with internet of things..like feeding the output screens of the apps to internet and monitoring them on a website in real time..if you could provide a little possible help i can pull it off..yes i'm studying electronics..i dint wanna take some journal and do a project related to it..i thought this was an interesting and a thoughtful instructable..i dont get much help from the professors here..so am trying my best to do it..
<p>Great ! :) I understand your trouble, don't give up. <br>But, I also have on my side projects that take a lot of time, and I do not know if I can correctly answer your questions in the future</p>
Thanks :-)..its okay..when you have time try to reply..thats fine!.
The jack coming from the phone connected to which part of the circuit?
<p>I'll try to simplify: the jack is composed of 4 wires (4 wires =&gt; 3 signal wires, 1 ground wire), so it's composed of 3 signals.</p><p>- the audio leftside (output of the phone)<br>- the audio rightside (output of the phone)<br>- the mic input (input of the phone)</p><p>The audio leftside is connected to the input of the circuit called &quot;1st signal generator&quot;.<br>The audio leftside is connected to the input of the circuit called &quot;2nd signal generator&quot;.<br>The mic input is connected to the output of the circuit called &quot;oscilloscope&quot;.<br></p>
Atleast give the single circuit which explains everything..its confusing!.have to finish this within a month :-/..someone help me ASAP..
<p>What is the &quot;single circuit which explains everything&quot; you are talking about ? This one ?</p>
I mean from the power supply it is connected to function generator output 2 circuit right?..i wanna know the interconnections..
hi I will finish the project put I have a question you put two led what is the purpose of each one I think one for regulate and the other one for high voltage and how you choose the values of the capacitor?<br>thanks<br>and I use bd243c and bf244c that's OK right ?
<p>The purpose of the first led is to regulate negative voltages, and the purpose of the second led is to regulate the positive voltages.</p><p>The value of the capacitor has been chosen by simulation of the circuit.<br><br>The bd243c and the bf244 seem OK to replace the d44h11 and the d45h11 that I used in this project :)</p>
<p>thanks i make the Oscilloscope but there are a lot of noise i mean when i connect the output to the phone i cant recognize the output</p><p>i then use a function generator and a professional Oscilloscope to see the output of the circuit and also i cant see the the output </p>
<p>Strange :/</p><p>Check if your capacitors are in the good position : the capacitors I used in my circuit are polarized. Also, check that the OP amp is correctly supplied and not damaged.<br>If your circuit still doesn't work, I recommend you to go to <a href="http://www.instructables.com/id/A-Preamplifier-for-Smartphone-Oscilloscopes/">the step 6 of the chipstein's Instructables</a>. He gives precious troubleshooting advices.<br><br></p><p>Once your circuit fully operationnal, the output signal will be quite clean like as mine :</p>
first thanks a lot for fast replaying <br>second I will try to check the opamp and the capacitor<br>
I want to test these circuits with proteus 8.How do i test the oscilloscope and function generator circuits?
<p>I'm not familiar with proteus, sorry.</p>
Did you use ATX power supply for the circuit? Not the normal one?
<p>You can use any kind of power supply, as far as it delivers +12V and -12V. I used an ATX power supply because it is able to deliver +12V, -12V and a lot of current (to supply a big speaker at the output of the circuit for example).</p>
I'm not getting that single piece of heat sink.I got 4 small pieces of heat sink.is it ok?..
<p>yes</p>
Can you suggest some alternatives? I'll try asking here..specify the exact purpose of those 2 transistors.
<p>Voltage amplification is done by the opamp, but the opamp alone cannot supply enough current to power a speaker. Transistors are current amplifiers.</p><p>By increasing the available output current, the power output increases:</p><p>P=V*I</p>
Exactly ! Thank you bigredlevy
<p>Loboat, nice tutorial.</p><p>I will certainly be putting one of these in my tool box.</p><p>I think you should note that having more than one ground connection point is not really necessary, and potentially hazardous if used improperly.</p><p>eg; the signal source from your device is connected to the input and ground of a circuit. only one probe is then required to test points throughout that circuit, no need for a second ground probe.</p><p>If a second ground probe is touched to any active point in the circuit under test, you will shunt that voltage to ground.</p>
<p>as an aside, if you are interested in measuring differential voltages, you could implement a circuit like this <a href="http://levysounddesign.blogspot.com.au/2016/02/differential-scope-probes.html" rel="nofollow">http://levysounddesign.blogspot.com.au/2016/02/dif...</a></p>
Can I also measure DC voltage?
<p>This circuit cannot measure DC due to the decoupling capacitor C5.</p><p>It would be impossible to measure DC using the microphone input of a phone.</p>
Specified Power transistors are not available here ..what are the equivalent? Even the bd243c and bf244c are not available
<p>this website has a function to find equivalent transistors. <a href="http://alltransistors.com/" rel="nofollow">http://alltransistors.com/</a></p><p>any complementary pair will work fine.</p>
<p>There are a lot of power transistors, but I don't know what alternatives are available to you in your country.</p>
Are those phone mic output, phone audio right, and phone audio left connected to each other? Thank you i hope you answer my questions
<p>I don't understand your question. Can you detail your problem ?</p>
Can i ask if the output in the first signal generator is in pin4? If you look at the data sheet of 324, pin4 is vcc and pin7 is the second output
<p>If you look at the circuit, the output of the signal generator is the output of the OP amp. <br>For example, if you use the first OP amp of the LM324 for this circuit, the output of the signal generator will be the output of the first OP amp: pin 1.</p>
Are those phone mic output, phone audio right, and phone audio left connected to each other? Thank you i hope you answer my questions
What you've used is a paid app or free one?
I used the free app called &quot;Function Generator&quot; and the paid app called &quot;Oscilloscope Pro&quot;. Both are for Android phones.
Thank you so much for your sharing.
Does it work with all kinda lab experiment circuits?
Yes !
thanks for fast answer.
sorry for the question I figured that the project want a transistor not a MOSFET

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Bio: My name is Loann Boudin, I'm a maker and a french student who study electronics engineering near to Paris. I love making stuff by ... More »
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