Connecting external self-made device to micro-usb port of the smartphone

I need to send some data represented by voltage changes to the smartphone. Can I send it directly to the data pins of micro-usb port? If some converters are needed what kind of them do you propose? Moreover what's the sampling frequency of typical smartphone to collect data from usb? 

Ruslan...I think you'd have to use some king of USB to serial converter chip at the very least to do this. Have you thought about using Bluetooth or Bluetooth Low Energy (BLE) to do this?  This avoids cables and connections and is probably only slightly more complex technically.There are lots of resources to assist you... here are some from Elektor magazine that I am familiar with:https://www.elektormagazine.com/magazine/elektor-201709/40732
This article is the first of a series of 6 and goes into a lot of detail on the use of the BLE600 module for communicating data to smartphones:https://www.elektormagazine.com/magazine/elektor-201503/27565
Unfortunately you need a subscription to get these articles.I am sure there are others here who can give you more specific advise on this as well

Hi Ruslan;For Bluetooth, you might want to look at the Simplee (www.sparkfun.com/simblee) or one of the Adafruit modules (www.adafruit.com/product/3406 or www.adafruit.com/product/1697). Both of those examples allow for reasonably easy two way communications between an external device and a cell phone.I've used both the Simblee and Adafruit Bluefruit without a lot of difficulty.
Another place to investigate would be using the audio jack. While I don't have personal experience with this, nor much direction, I have seen a few devices that use the audio jack as an interface. You'd have to do some more research in that direction.Duane

Hi Ruslan -- I agree with Duane -- I use Simblee modules a lot on my projects -- it's a small module (7mm x 10mm -- but you can get it on a 0.1" pitch breakout board) with a 32-bit processor and a Bluetooth processor -- it works with the Arduino IDE -- you can write a sketch that defines a user interface that appears on your Smartphone -- and you can use the Simblee to monitor digital and analog signals and display them on your Smartphone.I could write a column describing this in more detail if you would be interested (post a response here and also email me at max.maxfield(_at_)aspencore.com just to make sure)
Max

One of the problems that you'd likely encounter if you tried to use USB to get data into the phone is that the phone is not normally set up to receive data on it's own but rather acts in response to commands from whatever is attached.You would have to write a phone app to collect the data. Now with the Simblee and Bluetooth, that is much easier. Of course I don't know if it works for data collection. You might need something a bit different.I recently played around with an ESP8266 WiFi module. Similar idea except uses WiFi instead of Bluetooth.  I used Cayenne app developer for the app to collect data.  It seemed to work OK in my browser but the app was buggy when I tried it. It might work for you though...

Thank you very much all for your answers. Actually I don't need to practically build the system. I just need to theoretically know what's is the possible data rate through the micro-usb where the data is represented by voltage values. Initially I thought that different voltage values could be directly sent to the smartphone micro-usb and then it could be decoded using some apps. But now I believe that some  converter should be used which limits the possible sampling frequency of incoming signal. So I just wanted to know what's this theoretically possible sampling frequency and quantization levels of incoming signal.Thank you again for your responses. It means a lot for a simple student from a developing country.

Thank you Duane,Yeah I've heard about audio jack. But its sampling frequency is about 43 kHz. So I wanted to know what theoretically possible data rate sent through micro-usb port where data is represented by different voltage values. Now I believe that it's limited by voltage-to-serial converter, but I'm not sure.Again thank you very much for your response.

I believe most smartphones are USB 2.0 compliant so the maximum data rate is 480 Mbit/sec. Of this you will have some overhead so it is unlikely that you would achieve more than 400 Mbit/sec and likely less.
Since this USB data is digital and you are wanting to measure analog voltage then you will need an analog to digital converter (ADC).  ADCs come in a wide variety of resolution (number of bits per sample) and conversion rates (number of samples per second).  Naturally the higher resolution and higher speed ADCs are more expensive. So you select an ADC based on the best compromise you can afford.To see if you can transfer the ADC data at the maximum speed over USB you take the  ADC resolution and multiply by the conversion rate.For instance an 18 bit 1 MSps (Mega-sample per second) ADC would generate 18 Mbit/sec which is well within the capability of USB. I know there are faster and higher resolution ADCs out there but even then I suspect that the ADC will be the limiting factor and not the USB.If you want more information on ADC specifications and what is available, look at the Analog devices and Texas Instruments web sites.

RuslanI agree with Elizabeth in that you are more likely to be limited by your choice of ADC rather than the serial capabilities of the micro-usb port.Someone elsewhere mentioned the ESP modules for use over WiFi. I think some of those modules have ADC ports inbuilt but I have never programmed them.However using a PIC or similar microcontroller you could do the ADC and take care of USB connectivity all at once. Of course you still need some software app in the smartphone to handle the incoming data.If you do decide to build / experiment further and you are using
android, Building Android Apps is a good beginners guide as it uses
"plugable" modules to eliminate coding. You could quickly create a
"browser" that could possibly gather info from your ADC.Regards

USB 2.0 Isochronous mode is intended for steady data streaming, and offers speeds of 8 or 16 or 24 MBytes/sec. I have successfully run the output of an 8-bit 15-MSPS ADC through a Cypress CY7C68013A USB microcontroller (using a flipflop to divide the CY7C68013A IFCLK 30 MHz by two to clock the ADC data every other IFCLK pulse, as the CY7C68013A needs one IFCLK to switch buffers).