Technologies do not stand still, and keeping up with them is not always easy. There are new items that I would like to understand in more detail. This is especially true for a variety of electronic designers, allowing you to assemble almost any simple device step by step. Now among them are Arduino boards with their clones, and Chinese microprocessor computers, and turnkey solutions that already come with software on board.
However, to work with all of the above range of interesting new products, as well as to repair digital equipment, an expensive high-precision tool is required. Among such equipment is an oscilloscope that allows you to read frequency readings and carry out diagnostics. Often its cost is quite high, and novice experimenters can not afford such an expensive purchase. Here the solution comes to the rescue, which appeared on many amateur forums almost immediately after the appearance of tablets on the Android system. Its essence is to make an oscilloscope from a tablet with minimal costs, without making any modifications or modifications to your gadget, as well as eliminating the risks of damage to it.
What is an oscilloscope?
The oscilloscope - as a device for measuring and tracking frequency fluctuations in an electric network - has been known since the middle of the last century. All educational and professional laboratories are equipped with these devices, since it is possible to detect some malfunctions or make fine-tuning of equipment only with its help. It can display information both on the screen and on paper tape. Indications allow you to see the shape of the signal, calculate its frequency and intensity, and as a result determine the source of its appearance. Modern oscilloscopes allow you to draw three-dimensional color frequency graphs. Today we will focus on a simple version of a standard two-channel oscilloscope and implement it using the prefix to a smartphone or tablet and the corresponding software.
The easiest way to create a pocket oscilloscope
If the measured frequency is in the range of frequencies heard by the human ear, and the signal level does not exceed the standard microphone, then you can assemble the oscilloscope from your tablet on the Android device without any additional modules. To do this, it is enough to disassemble any headset, on which a microphone must be present. If there is no suitable headset, then you will need to buy a 3.5 mm audio plug necessarily with four contacts. Before soldering the probes, check the pinout of the connector of your gadget, because there are two types of them. The probes must be connected to the pins corresponding to the microphone connection on your device.
Next, download software from the Market that can measure the frequency at the microphone input and draw a graph based on the received signal. There are a lot of such options. Therefore, if desired, there will be plenty to choose from. As mentioned earlier, it did not require reworking the tablet. The oscilloscope will be ready immediately after calibrating the application.
Pros and cons of the above scheme
The advantages of such a solution clearly include the simplicity and low cost of assembly. An old headset or one new connector costs almost nothing, and it only takes a few minutes to complete the time.
But this scheme has a number of significant drawbacks, namely:
- A small range of measured frequencies (depending on the quality of the sound path of the gadget ranges from 30 Hz to 15 kHz).
- The lack of protection for the tablet or smartphone (if you accidentally connect the probes to parts of the circuit with high voltage, you can at best burn the chip responsible for processing the audio signal on your gadget, and in the worst, completely disable your smartphone or tablet).
- On very cheap devices, there is a significant error in the measurement of the signal, reaching 10-15 percent. For fine tuning of the equipment, such a figure is unacceptable.
Realization of protection, signal shielding and error reduction
In order to partially protect your device from possible failure, as well as to stabilize the signal and expand the input voltage range, a simple oscilloscope circuit for a tablet can be used, which has long been successfully used to assemble computer devices. It uses cheap components, including KS119A zener diodes and two 10 and 100 kOhm resistors. Zener diodes and the first resistor are connected in parallel, and the second, more powerful, resistor is used at the input of the circuit to expand the maximum possible voltage range. As a result, a large amount of interference disappears, and the voltage rises to 12 V.
Of course, it should be borne in mind that the oscilloscope from the tablet works primarily with sound pulses. Therefore, it is worth taking care of high-quality shielding of both the circuit itself and the probes. If desired, detailed instructions for assembling this scheme can be found on one of the thematic forums.
Software
To work with such a scheme, a program is required that can draw graphs based on the incoming audio signal. Find her in the "Market" is easy, there are many options. Almost all of them require additional calibration, so you can achieve the highest possible accuracy, and make a professional oscilloscope from a tablet. Otherwise, these programs perform essentially the same task, so the final choice depends on the required functionality and ease of use.
Homemade prefix with a Bluetooth module
If a wider frequency range is required, then the above option will not be limited. Here a new option comes to the rescue - a separate gadget, which is a prefix with an analog-to-digital converter, which provides signal transmission in digital form. The audio path of the smartphone or tablet is no longer used in this case, which means that higher measurement accuracy can be achieved. In fact, at this stage they are only a portable display, and all information is already collected by a separate device.
You can assemble the oscilloscope from a tablet on an Android with a wireless module yourself. There is an example on the network when, in 2010, a similar device was implemented using a two-channel analog-to-digital converter based on the PIC33FJ16GS504 microcontroller, and the LMX9838 Bluetooth module served as a signal transmitter. The device turned out to be quite functional, but difficult to assemble, so for beginners to make it will be an impossible task. But, if desired, to find a similar project in the same amateur forums is not a problem.
Ready-made consoles with Bluetooth
Engineers are not asleep, and, in addition to handicraft crafts, more and more consoles appear in stores that perform the function of an oscilloscope and transmit a signal through a Bluetooth channel to a smartphone or tablet. The oscilloscope-prefix to the tablet, connected via Bluetooth, often has the following main characteristics:
- Limit of the measured frequency: 1 MHz.
- Probe voltage: up to 10 V.
- Radius: about 10 m.
These characteristics are quite enough for domestic use, and yet in professional activities sometimes there are cases when this range is sorely lacking, and it is simply unrealistic to implement a larger one with a slower Bluetooth protocol. What solution can there be in this situation?
Wi-Fi Oscilloscopes
This option of data transfer significantly expands the capabilities of the measuring device. Now the market for oscilloscopes with this type of information exchange between the console and the tablet is gaining momentum due to its relevance. Such oscilloscopes are practically not inferior to professional ones, because without delay they transfer the measured information to the tablet, which immediately displays it in the form of a graph on the screen.
Management is carried out through simple, intuitive menus that copy the tuning elements of conventional laboratory devices. In addition, such equipment allows you to record or broadcast in real time everything that is happening on the screen, which can become an indispensable tool if you need to ask for advice from a more experienced master located in another place.
The characteristics of the oscilloscope for tablet repair in the form of a set-top box with Wi-Fi connection grow several times, compared with previous versions. Such oscilloscopes have a measurement range of up to 50 MHz, while they can be modified using a variety of adapters. Often, batteries are installed in them for autonomous power supply, in order to maximize the load on the workplace from unnecessary wires.
Home-made versions of modern oscilloscope prefixes
Of course, on the forums there is a surge of various ideas with the help of which enthusiasts try to realize their old dream - to independently assemble an oscilloscope from a tablet on an Android with a Wi-Fi channel. Some models are successful, others are not. Then it remains for you to decide whether to try your luck too and save a few dollars by assembling the device yourself, or purchase a ready-made version. If you are not confident in your abilities, then it is better not to take risks, so as not to regret the wasted funds later.
Otherwise, welcome to one of the ham radio communities where you can be given good advice. Perhaps later, it is according to your scheme that beginners will collect their first oscilloscope in their life.
Console Software
Often, along with purchased oscilloscope prefixes, a disk with a program is delivered that can be installed on your tablet or smartphone. If such a disk is not included, then carefully read the instructions for the device - most likely, it contains the names of programs compatible with the console and located in the application store.
Also, some of these devices can work not only with devices running the Android operating system, but also with more expensive "apple" devices. In this case, the program will definitely be in the AppStore, since there is no other installation option. Having made the oscilloscope from the tablet, do not forget to check the accuracy of the readings and, if necessary, calibrate the device.
USB Oscilloscopes
If you don’t have a portable device like a tablet, but you have a laptop or computer, don’t be upset. You can also make an excellent measuring device out of them. The simplest option is to connect the probes to the microphone input of the computer according to the same principle as described at the beginning of the article.
However, given its limitations, this option is not suitable for everyone. In this case, a USB oscilloscope can be used, which will provide the same characteristics as a set-top box with Wi-Fi signal transmission. It is worth noting that such devices sometimes work with some tablets that support the technology of connecting external OTG devices. Of course, they also try to make a USB-oscilloscope on their own, and quite successfully. At least, this topic is devoted to a large number of topics on the forums.