# DIY mobile phone. Part 1

Recently on a habr there was a post about how some craftsmen from Massachusetts Technological created a "home-made" mobile phone. I think it’s time to prove that our Monsieurs also know a lot about ... uh ... exquisite pleasures.
So, I present to your attention a mobile phone assembled almost “on the knee”!

I ask all interested under cat. Lots of pictures!

Due to the significant amount of material, the article will be in two parts. The first part will describe the hardware, and the second part will examine the AT-commands of the module and give examples of their use.
So, let's begin.

##### Short description

The “heart” of the phone is the Quectel M10 GSM module, which has wide functional capabilities, including both telephone communications and data transmission. The device also has a power source that allows you to power the device from a 12V source (for example, a lead-acid battery), an RS-232 interface, a keyboard, an antenna, a SIM card holder and a headset jack.

M10-TE-A module.

##### Power Supply

The power supply unit provides power to the device with voltages + 4.1V (current up to 2A), + 5V (current up to 500 mA), + 3.3V (current up to 100 mA). 4.1V voltage is needed to power the GSM module. GSM-modules have very high demands on the power source. The power supply of the module must have a voltage of 3.4 V to 4.5 V at a current of up to 2 A, while the ripple amplitude during a step-like change in the load current from zero to maximum should not exceed 400 mV. In fig. 1 shows the allowable amplitude of the ripple of the supply voltage during operation of the module.

Fig. 1. Permissible ripple of the supply voltage during the operation of the GSM module.

Initially, it was assumed that the device will contain a microcontroller with a supply voltage of 3.3 V and a display, which will need 5V to power the backlight. At this stage, suppose that the current through the 5V channel does not exceed 0.5A. The input voltage of the power supply is chosen equal to 12V. The electrical circuit diagram is shown in Fig. 2.

Fig. 2. Power supply circuit ( pdf )

The circuit is not without drawbacks, and mainly uses what I had "at hand". For serial production, such a solution, of course, is not very suitable, but for experiments it is quite suitable. We will not dwell here on the operation of this circuit and on the calculation of the ratings, since they are elementary and described in detail in the documentation for the corresponding microcircuits.
So, we assemble the circuit on a breadboard (Fig. 3) and conduct tests under load, while controlling the temperature of the fuel elements. Tests completed successfully.
If you intend to use only the GSM module, without other nodes, then sources + 5V and 3.3V are not needed.

Fig. 3. Power supply board

##### Keyboard board

The layout of the keyboard board is almost unchanged from the documentation for the module. However, after it was assembled, it turned out that a number of buttons are not supported by this version of the module. In principle, you can not connect the keyboard to the module at all, all actions with the module can be performed using AT-commands via UART.
The keyboard layout is shown in Fig. 4. Diodes serve to protect the module from static voltage.

Fig. 4. Keyboard layout ( pdf )

Fig. 5. Keyboard board

##### GSM module board

We pass to the main board.
Since the device is assembled on a breadboard, I decided not to use the Quectel M10 module, which is soldered to the board, but its “derivative”, the module with the M10-TE-A module, which has an IDC connector with a contact pitch of 1.27 mm (two-row socket). The antenna is connected to a special small connector (GSC) via the GSC-SMA adapter. In a serial device, on a normal board, of course, it makes sense to use the usual M10 module. It should be borne in mind that the M10 and M10-TE-A have different pin numbers, so the circuit also needs to be adjusted.

So, the circuit board:

Fig. 6. GSM circuit diagram ( pdf )

And the circuit itself:

Fig. 7. GSM board

The circuit contains a module, a SIM card holder, a headset jack, a keyboard connector and a pair of microcircuits: an RS-232 interface and an auxiliary microcircuit for connecting to a piezoelectric emitter module and an LED. There are no special circuitry frills here, almost everything is taken from the documentation for the module.
A few more words about connecting the keyboard. Since the ROW3, ​​ROW4 rows and the COL4 column are not used by the module, I decided to use them for the on and off buttons of the module.
The phone also does not have a display. Although the module has conclusions for direct connection of the display, it still cannot be connected, since this function (like many others) is disabled for the modules that go on public sale.
To power the real-time clock, an ionistor is used (a capacitor with a capacity of 1F, a large round thing on the board). If the clock is not needed, it can be omitted.

##### Assembly

So, it's time to assemble our constructor:

Fig. 8. Everything is ready for assembly

Fig. 9. Phone assembly.

Now you can insert a SIM card, connect power, connect the phone to a computer via the COM port, and proceed with the study of AT commands.

A few words about the budget.

##### Budget

Module Quectel M10-TE-A 665.64 r.
Antenna 120 p.
SIM card holder SCV-W2523X-06-LF 21.80 r
Cable adapter GSC-SMA - 161.86 r.

The remaining components were found within a radius of three meters.

##### In conclusion of the first part

In the next part, AT commands supported by the module will be discussed.

##### References

Unfortunately, the manufacturer’s website provides far from complete information about the module. Most pdf files are not publicly available, however, you can find some of them on the network. I took the trouble to collect these files and upload them for download.

1. M10_ATC_V1.03.pdf - reference on AT commands of the M10 module
2. M10_EVB_UGD_V1.01.pdf - description of the debug board based on the M10 module
3. M10_GSM_Module_Specification.pdf - a brief description of the M10 module
4. M10_HD_V1.02.pdf - Hardware Design
5. M10-TE-A_HD_V1.01.pdf - description of the board based on the M10 module
6. GPRS_Startup_UGD_V101.pdf - install the modem in Windows
7. GSM_UART_AN_V100.pdf - connect devices to UART
8. RF LAYOUT_AN_V1.0.pdf - connecting the antenna to the module
9. GSM_Location_ATC_V10.pdf - requesting coordinates and time

Documents describing work with FTP, HTTP, MMS, SMTP and TCP / IP, respectively:
10. GSM_FTP_ATC_V100.pdf
11. GSM_HTTP_ATC_V100. pdf
12. GSM_MMS_ATC_V101.pdf
13. GSM_SMTP_ATC_V11.pdf
14. GSM_TCPIP_AN_V101.pdf