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3G technology is the latest in mobile communications. 3G stands for "third generation"--this makes analog cellular technology generation one and digital/PCS generation two. 3G technology is intended for the true multimedia cell phone--typically called smartphones--and features increased bandwidth and transfer rates to accommodate Web-based applications and phone-based audio and video files.
3G comprises several cellular access technologies. The three most
common ones as of 2005 are:
CDMA2000 - based on 2G Code Division Multiple Access (see Cellular Access Technologies)
WCDMA (UMTS) - Wideband Code Division Multiple Access
TD-SCDMA - Time-division Synchronous Code-division Multiple Access
3G networks have potential transfer speeds of up to 3 Mbps (about 15 seconds to download a 3-minute MP3 song). For comparison, the fastest 2G phones can achieve up to 144Kbps (about 8 minutes to download a 3-minute song). 3G's high data rates are ideal for downloading information from the Internet and sending and receiving large, multimedia files. 3G phones are like mini-laptops and can accommodate broadband applications like video conferencing, receiving streaming video from the Web, sending and receiving faxes and instantly downloading e-mail messages with attachments.
3G is a cell phone network protocol.
In the dark ages before Mobile phones, people who really needed mobile-communications ability installed radio telephones in their cars. In the radio-telephone system, there was one central antenna tower per city, and perhaps 25 channels available on that tower. This central antenna meant that the phone in your car needed a powerful transmitter -- big enough to transmit 40 or 50 miles (about 70 km). It also meant that not many people could use radio telephones -- there just were not enough channels.
The genius of the cellular system is the division of a city into small Mobiles. This allows extensive frequency reuse across a city, so that millions of people can use Mobile phones simultaneously.
A good way to understand the sophistication of a Mobile phone is to compare it to a CB radio or a walkie-talkie.
Full-duplex vs. half-duplex - Both walkie-talkies and CB radios are half-duplex devices. That is, two people communicating on a CB radio use the same frequency, so only one person can talk at a time. A cell phone is a full-duplex device. That means that you use one frequency for talking and a second, separate frequency for listening. Both people on the
Channels - A walkie-talkie typically has one channel, and a CB radio has 40 channels. A typical Mobile phone can communicate on 1,664 channels or more!
Range - A walkie-talkie can transmit about 1 mile (1.6 km) using a 0.25-watt transmitter. A CB radio, because it has much higher power, can transmit about 5 miles (8 km) using a 5-watt transmitter. Mobile phones operate within Mobiles, and they can switch Mobiles as they move around. Mobiles give Mobile phones incredible range. Someone using a Mobile phone can drive hundreds of miles and maintain a conversation the entire time because of the cellular approach.
In full-duplex radio, the twotransmitters use different frequencies,
so both parties can talk at the same time.
Mobile phones are full-duplex.
In a typical analog Mobile-phone system in the
Because Mobile phones and base stations use low-power transmitters, the same frequencies can be reused in non-adjacent
Each
Many old Nokia cellular phones have graphical LCDs based on the PCD8544 controller. These are perfect for various electronic projects with microcontrollers. The interface is a two-wire serial type (clock and data), and some additional signals. The LCD supply is a single 3.3 V with very low supply current. This is not really a "hack"; we are merely re-using parts of the phone.
Note that information here is for the Nokia 6150 specifically. However many older models (e.g. Nokia 5110) are very similar, and hence most stuff is applicable also to those. Below is an image showing the different parts of the front PCB (back side has no components).
Note how the keypad is partly divided into rows and columns. This is because those keys are multiplexed in this way. The other keys are more or less randomly connected to the rows and columns. Each button has an edge area and a center are, between which a short-circuit is created when the button is pressed. The upper switch is used to turn the phone on and off, and the buzzer is what emits the loud beep when e.g. receiving an SMS. The three testpads are connected to the phone's internal circuits, and have no real use in this context.
Since the LCDs only have the conductive-rubber type of connection, the easiest method of hooking a microcontroller up to it is to re-use the whole PCB. The connection on the back has two rows of 14 pins each, which I numbered A1 through A14 and B1 through B14.
The image below shows the numbering convention I have used. Note that the ribbon cable was soldered to the board as part of the hack. It is normally not there when you open the phone.
A table below describes the function of each pin.
Pin | Function | Explanation |
A1 | LED & buzzer ground | |
A2 | Switch output | Shorted to A8 (ground) when switch is pressed |
A3 | LCD D/C | Selects data (high) or command (low) for LCD communication |
A4 | LCD SCLK | LCD serial clock |
A5 | LCD SDIN | LCD serial data |
A6 | LCD /SCE | LCD chip enable (active low) |
A7 | LCD /RES | LCD reset (active low) |
A8 | Ground | LCD ground supply, middle testpad, switch ground |
A9 | Buzzer control | |
A10 | LCD Vdd | Positive supply for LCD (2.8 - 3.3 V), LCD Osc (note 1) |
A11 | not connected | |
A12 | LED control | Set high to turn on LEDs |
A13 | Speaker 1 | Differential driving through passive filter (?) |
A14 | Speaker 2 | Differential driving through passive filter (?) |
B1 | LED & buzzer positive supply | Ca +3.9 V supply (note 2) |
B2 | Connected to B3 | |
B3 | Connected to B2 | |
B4 | Leftmost testpad | |
B5 | Row 4, "right" edge | |
B6 | Row 3, "down" center, "hang up" center | |
B7 | Row 2, "answer" center, "up" center | |
B8 | Row 1, "left" center | |
B9 | Rightmost testpad | |
B10 | Column 3, switch output (through diode) | (note 3) |
B11 | Column 2 | |
B12 | Column 1 | |
B13 | "Left" edge, "up" edge, "down" edge, "right" center | |
B14 | "Answer" edge, "hang up" edge |
Note 1: A decoupling capacitor is installed between LCD Vdd and LCD ground on the PCB.
Note 2: The LEDs are driven by a constant-current circuit, equal to (0.5*U(A12) - 0.7)/15 A for the display LEDs and (0.6*U(A12) - 0.7)/15 for the keypad LEDs. These formulas are valid as long as U(B1) is larger than 2.0 + 0.6*U(A12), which gives approx. 3.9 V as lower limit, but this is not critical. However, buzzer requires more than 3.3 V.
Note 3: The anode of the diode is connected to B10, and cathode to the switch output. Not sure why this wiring is used...
The LCD operates in the range 2.8 - 3.3 V, and hence all other signals should also be within that range. To use the LCD, required signals are: A3, A4, A5, A6, A7, A8, and A10. I will not go into details about how the signals are used, how stuff is written to the LCD, etc, since that is covered by the PCD8544 datasheet. However, I will give a proper initialization sequence, which is useful for checking that the LCD is working:
The LCD should now show a vertical pattern of 10101010 in the top leftmost corner. You can download an ASM file for Atmel's microcontroller ATmega8. The file contains a program that writes some stuff to the LCD and then turns the contrast up & down repeatedly.
Once the basic communication is working, doing graphics on the LCD is not very difficult: