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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.

Step 2: Parts, Tools, & Skills

Here are the materials, tools and skills that you will need for this project.

PARTS:



• (1x) Phone with an internet connection
• (1x) Old CD Driver (for the box)
• (1x) 30 x 30 cm Wood Plank
• (1x) 10 x 4.5 cm Stripboard
• (1x) Heat Sink
• (1x) Switch
• (1x) SPDT Switch
• (30 cm long) 4 Wires Cable
• (1.50 m long) Electrical Wires
• (1x) 3.5 mm Bipolar LED
• (3x) 4 mm Black Banana Sockets
• (3x) 4 mm Red Banana Sockets
• (4x) Male Jack Connector (TRRS)
• (2x) Female Jack Connector (TRRS)
• (3x) Potentiometer Knobs
• (1x) Quadruple OP Amplifier (LM324) or (4x) Single OP Amplifiers
• (1x) +8V Voltage Regulator (7808)
• (1x) -8V Voltage Regulator (7908)
• (1x) Power NPN Transistor (D44H11)
• (1x) Power PNP Transistor (D45H11)
• (1x) 1MΩ Potentiometer
• (2x) 100kΩ Potentiometers
• (1x) 330kΩ Resistor
• (x1) 100kΩ Resistor
• (x1) 33kΩ Resistor
• (4x) 10kΩ Resistors
• (x1) 3.3kΩ Resistor
• (1x) 1.5kΩ Resistor
• (1x) 100Ω Resistor
• (1x) 22µF Capacitor
• (2x) 10µF Capacitors
• (1x) 4.7µF Capacitor
• (1x) 1µF Capacitor



TOOLS:



• soldering iron and solder wire
• saw
• cutter
• flat pliers
• cutting pliers
• screwdriver
• ruler
• drill
• duct tape
• glue gun and glue sticks


SKILLS:



• basic soldering skills
• basic woodworking skills


This project can be built for under $25 by purchasing all the parts, but you can make it for less by using leftover parts. The potentiometers, the capacitors, the bipolar LED, the wires, and some resistors used in this project are from old electronics.

Step 3: Downloading the Signal Generator App

Before putting on the soldering iron and starting assembly, download the applications to your phone. Check the compatibility of these apps on your phone is the first step of this project.

It just takes a few minutes, and can give you the motivation and conviction to make the project if you hesitate.

Note: I have an Android phone and I used for this project Android apps from the Google Play Store. There are similar applications for Apple users, but I haven't tested them yet.


The Signal Generator app:

To generate various waveforms with your phone, you'll need an application that generate a sound (a signal) to the audio output of your phone. Hopefully, many apps can do this job!

For Android devices:

For Apple devices:


The signals generated by these apps go directly to the audio output of the phone : to the phone speaker if there isn't headphones plugged, or to the jack output if the phone detects headphones.
I wanted an electronic signal (not a sound) in exit of the phone, so I decided to use the jack output. So, the electronic signal comes out the phone by the jack output and goes to the electronic circuit with a jack cable.

The signal generator application chosen for this project (Function Generator) takes advantage of the smartphone stereo output : the first channel of the signal generator is connected to the left audio side, and the second one is connected to the right audio side.
So, you dispose of 2 separated signal channels (left and right) using the single audio output of your phone!

Step 4: Downloading the Oscilloscope App

As for the Signal Generator applications, I haven't tested the Oscilloscope ones for Apple devices yet.

The Oscilloscope app:

To visualize an electronical signal on your phone, you'll need an application able to receive and display the waveform of the sound (the signal). Some apps have been created for this purpose, here is a list of them.

For Android devices:

For Apple devices:

These apps allow you to visualize the signal coming from the mic input.

Step 5: The Electronic Circuit

The Electronic Circuit of this project is composed of 4 parts:



1. The power supply circuit
2. The Oscilloscope input circuit
3. The first output circuit of the Signal Generator
4. The second output circuit of the Signal Generator




• The power supply circuit


To support and process sinusoidal signals, the OP Amplifiers in the system need to be supplied with asymmetric voltages. The entire project is supplied with +12V and -12V, which are converted to + 8V and -8V by the 7808 positive voltage regulator and the 7908 negative voltage regulator.

The capacitors C1, C2 and C3 are used to avoid voltage drops when a high current is requested from an output.



• The Oscilloscope input circuit


The actual Oscilloscope input circuit is a slightly modified version of the chipstein's circuit in his "Preamplifier for Smartphone Oscilloscopes", where I changed a few of the resistor and the capacitors values.

First, the 1µF capacitor blocks any DC input and then the potentiometer adjusts the signal attenuation. If the incoming signal is still too high for the phone's microphone input, a second signal attenuation by 10 is performed by swaping the switch between the low and high ranges.

An OP amplifier in unity-gain buffer mode receives the attenuated signal, and adjusts the high impedance circuit. It also helps provide some extra power to the rest of the electronic assembly.

The 100 Ω resistor and the bipolar LED limit the voltages reaching the phone to about ±1.8 V, and also warn you when signals higher than that are present.

A 4.7µF capacitor is used to isolate the mike input from DC on the preamp output and a 1.5 kΩ resistor is connected between the output and ground to allows the phone recognize an external source.

If the final signal is not too large for the phone and that the warning led is off, the last switch allows you to connect the phone to the circuit

I recommend to see his tutorial to find out more informations about the possibility of this circuit !




• The first output circuit of the Signal Generator


The first output circuit of the Signal Generator use a potentiometer to amplify the signal coming out the phone audio output, up to 11 times. The OP Amplifier isn't able to provide high current output of this assembly. It is therefore intended to provide a signal to a small circuit.



• The second output circuit of the Signal Generator


The second output of the signal generator circuit uses the same circuit as above for the signal amplification. The waveform generated by the phone can be amplified up to 11 times using the AOP, the potentiometer and resistors. This circuit also includes a power stage (called push-pull), using two power transistors and voltages coming from the voltage regulators. It therefore allows to feed important circuits up to 2A, like a loudspeaker, an audio amplifier, or even bigger...


Note : I included at this step the Eagle schematic file if you want to make modifications and improvements.

Step 6: Populating the Stripboard

Start by soldering an IC carrier in the stripboard center.

Solder the resistors, capacitors, transistors and voltage regulators, while respecting the electronic schematic.

The switches, the LED, the potentiometers, the jack female connectors and the power connectors will be connected to the project enclosure. To connect them to the stripboard, it is necessary to use electrical wires: cut as much electrical wires as required and use duct tape and pen to identify them.

Once the heat sink screwed on the voltage regulators and the transistors, it is very difficult to identify wires: now you understand why naming them is very helpful! ;)

Double check your wiring before going to the next step !

Step 7: Making the Cables

In this project, the exchange of signals between the electronic circuit and the phone is constant.

First, the signal generator simulated on the phone should be able to send waveforms to the right and left outputs of the stereo jack.

Then, the oscilloscope simulated on the phone must be able to receive an electrical signal using the microphone input of the phone.

The only way to make all these connections between the phone and the circuit is to use a 3.5 mm jack cable with 4 poles. Thus, the use of the oscilloscope or the signal generator is done with a single cable.

To make this cable, start by cutting a 4 wires cable of 30 cm long. Then solder to each end a jack male connector, respecting the same wiring on each end.

This cable will be like an extension cable between two female jacks.

An extra cable can be made to use a second phone with this project.

Step 8: Preparing the Box

The project Oscillophone uses an old CD driver as box. Once the CD driver open and its contents removed, it is large enough to hold the electronic circuit and all the connectors.

In addition, a metal box like this is extremely useful for this type of project: the electronic circuit maked for this project process with small electronic signals sensitive to external electric and electromagnetic pollution. The metal box of the CD player surrounding the circuit acts as a Faraday cage, preventing the external disturbances to change the shape of the signals.

Step 9: Drilling the Holes

The inside cover of the CD driver is lined with duct tape to prevent shorting with the bottom of the stripboard.

To arrange the potentiometer closer to the user, three holes are drilled on the top cover of the CD driver. Then, the potentiometers are inserted into the holes and secured with rubber washers. The potentiometer to the left is the 1MΩ (for the oscilloscope) while the other two are the 100kΩ (for the signal generator).

Step 10: Cutting the Wooden Parts

The front and the rear of the project box are made by cutting two strips of wood.

6 holes are drilled on the front face, then the banana sockets are implemented there.

A seventh hole is drilled above the connectors dedicated to the oscilloscope, to implement the warning led.

The rear face is pierced with 3 holes, 2 for female jacks and one for the power supply wires.

Step 11: Finalize the Box

To finalize the box, all the wires of the electronic circuit are connected and soldered to their connectors (switches, potentiometers, banana sockets, female jack, led, power supply wires...), then stripboard and wood strips are glued to the box using the glue gun.

Finally, the top cover of the CD driver is screwed and potentiometers knobs are installed.

Step 12: Making the Phone Stand

The last fabrication step is creating a stand for the phone. It consists of 3 pieces of wood glued together.

The assembly is then glued on the upper side of the CD driver using a glue gun.

Step 13: See the Result Works!

To see the result works, connect the male jack cable to the phone and to the female jack of the circuit.

To test the proper operation of the signal generator, connect a speaker to the signal generator output power, and generate a low frequency sinusoidal signal (between 300Hz and 1kHz). You should hear a sound from the speaker, becoming more and more acute when the applied frequency becomes high.

A more rigorous test consists to visualize a signal from the signal generator output on a professional oscilloscope, and compare it to the output of a professional signal generator.

The result is quite impressive: the output signal of this project is of course poor compared to professional signal generator, but remains usable and accurate enough.

The oscilloscope input of this project works perfectly: the warning LED limits the signal up to ±1.8V and allows the user to know when the input signal is too high. If this is the case, it is necessary to change the rank of the signal attenuation at a higher level. The signal can then be visualized on your phone, using the oscilloscope app.

Step 14: Limitations and Improvements

  • Limitations

The audio bandwidth of mobile phones is reduced to human audible signals. This means that the signal generator and the oscilloscope apps will be able to generate and process signals from about 150Hz to 15kHz, although the signal generator app can generate signals up to 22kHz. Beyond this bandwidth, the signals are more and more weaker, with a lower quality.

Obviously, this project can not compete with the quality of professionals signal generators and oscilloscopes. The Oscillophone is dedicated for students studying electronics and makers. If you must work regularly with electronic signals, invest in oscilloscopes and signal generators is not a waste of money!

An important limitation of this project is the simultaneous use of the signal generator and the oscilloscope. On my Android phone, when the Function Generator app is opened and then reduced in the background, the sound generated is turned off. This prohibits the use of both applications at the same time and seriously undermines the usefulness of this project on some circuit.

However, some phones (like Galaxy S5) and other tablet are able to open two applications at a time. A next version of Android will extend this functionality to all phones.

Another solution is to use two phones: one as a signal generator, the other as oscilloscope. This option has been made during the assembling of this project, which integrate two jack female connectors in parallel to the circuit and 2 jack cables.

  • Improvements

Even if the phone is highly protected from high voltages by the electronic circuit, it is not completely disconnected from the parts. A way to protect the phone against a very high voltage (even more than 1000 volts) is to use galvanic isolation: optocouplers. These component uses light to transmit a signal and thereby completely isolating the phone.

Another possible improvement concerns the power supply circuit. Currently, the circuit is powered by an DIY ATX power supply. An integrated power supply in the housing could improve the portability of the project.

<p>Can We Use Any App With This Hardware or Recommended one's are better....</p><p>Is Blue tooth Osciloscopes have any advantage or disadvantage over this ....</p>
You can use any app with this hardware. I recommended the ones i found great for my purpose. <br><br>Bluetooth oscilloscopes have the main advantage to be totally isolated from the input signal. There's no possible way that your phone can be damaged in case of trouble. <br>But, they are more complicated to build : you will need prog skills in addition to electronics skills.
<p>How about if we were to connect our 3.5mm jack to a bluetooth module and then were to pair that with the phone and open the apps.</p><p>Wouldn't it only require only 1 extra component?</p>
<p>You mentioned that it measure upto 1.8V. Can we increase the voltage measuring range.</p>
<p>Hi, sorry. I'm confuse. There are two female jack connector at the rear side, for two range of signal generator. If using as an oscilloscope, i need to add one more female jack connector (output). So total 3 female jack connector?</p>
<p>can you provide block diagrams for explain the working.?</p>
<p>there are ERC errors on Eagles schematic diagram. </p>
<p>Possible... I used Eagle for the schematic representation of the circuit, but I didn't do any routing with it. If you want to, you have to do some modifications :)</p>
<p>What can be the alternative of those transistors ? If there isn't, I think it's ok to copy the first signal generator signal output instead of the second, right ?</p>
<p>Nice, i'll make it soon!</p>
<p>Is there any way to test function gernator and oscilloscope circuits without connecting to mobile phone ........ ?</p>
<p>Yes, with an oscilloscope and a function generator :) (as I explained in the step 1, &quot;How to use these devices&quot;).<br>It's the only way</p>
<p>Right :)</p>
<p>Is there any way to test function gernator and oscilloscope circuits without connecting to mobile phone ........ ?</p>
<p>Can We add bluetooth module to this circuit (and use built-in App) ....... </p><p>Can anyone provide Proteus File Like Eagle files are provided ......</p>
<p>no, unless you change the circuit and the all project...</p>
<p>Can you refer a good project on Bluetooth Oscilloscope</p>
I finally made it :D<br><br>Revewing my problems:<br>After many many tries I made the entire circuit today. The problem I was facing was that I thought that the eagle schematics were representing the LM324 pins but that wasn't the case. Connecting each circuit represented in Eagle schematics provided to an op-amp In the LM324 solved the problem therefor I ended up using all 4 op amps of the LM324 for the 4 provided Eagle schematics circuits.<br><br>Tansistors not found:<br>I couldn't find the D44H11 so I tried BD226 NPN power transistor instead, simmilerly the D45H11 was replaced by a BD227 PNP power transistor and they work flawlessly. <br><br>Using my Nexus tablet (2012) and the app called Function generator I was able to produces many wave forms with good frequency range, noise, amplitude, duty cycle etc..Also the oscilloscope works as it should.<br><br>Thank you loboat fot the great project and I really wish that you include a note that the Eagle schematics are not related to the LM324 pins ;)<br><br>
<p>A follow up... </p><p>After getting everything soldered on a Pcb board the 2 function generators are working great but the oscilloscope is not working anymore!! All i get is a small noise even if the is nothing connected to the scope input..</p><p>One more thing, I an using a single Trrs cable pluged to the phone were the ground GND of all circuits are connected to the trrs cable. should it be fine or should I use a separate cables for Fun.generators and the oscilloscope?</p>
<p>I think there is something wrong with the first few nction generator. Pin7 of the opamp was not used as an output, instead you have used pin4 and the common which I can't understand why? Could you explain please :)</p>
<p>There is no relationship between the pin numbers of the lm324 and the pin numbers of the OP amps used in the eagle schematic. That's why ! :)<br>Just make the circuit using the 4 OP amps of the lm324 </p>
<p>is 1 Ampere enough to supply this project?</p>
<p>the voltage regulator 7808 and 7908 does it have a current rating of 1A?</p>
<p>Yes. You can check this specification by studying the lm7808's datasheet (you can find it with a quick google search btw)</p>
<p>the voltage regulator 7808 and 7908 does it have a current rating of 1A?</p>
<p>Awesome,thank you very much!Just to say that in my image i have an </p><p>asymmetrical power supply(try to fix it) thats why i have this screen on the phone</p>
<p>Congratulations !! I hope this project will be usefull for you :)</p>
May i know the cost of this project
<p>see step 2 for the total cost !</p>
<p>Hi, I can't find any of both transistor you (or anyone in the coments) suggested, so: Can I use 2SD1265 NPN transitor instead of the D44H11? or maybe, could you please suggest me any other transistors that should work with the project and I could ask to my seller?</p>
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="https://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>

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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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