🍫 🤡 🖨️ GSM telephone with disk dialer ↗️ 📩 ⬜️

Surely, many radio enthusiasts had an idea to adapt a telephone with a disk dialer for mobile radio communications.

Wired communication is gradually becoming a thing of the past, and such devices are gathering dust on a shelf. I always liked the look of such devices. I could not resist and two years ago I decided to remake the telephone, which still works, without failures.

In addition to the telephone, the following devices are needed:

any button mobile phone;
lithium-ion battery size 18650 and a device for charging it (Power bank);
USB BF micro splitter cable (female) -2 x USB BM micro (male);
controller on the ATtiny2313 chip.

Electronics

Microcontroller bundle diagram with a mobile phone and a dialer.

First of all, it is necessary to solder to the contacts of the buttons of the mobile phone, the cable loop and connect to the controller. A controller to teach how to dial when dialing the corresponding numbers on the disk. Most likely, the layout of the buttons on most mobile phones will be similar. For my scheme, it is necessary: one common wire for groups of buttons 1-4-7, 2-5-8-0 and 3-6-9 and a wire for each digit; a pair of conductors to the call, cancel, and toggle buttons from one SIM card to the second.

After soldering, we collect the mobile phone back into the case and fasten it inside the telephone with brackets. I mounted the mobile phone with the display facing down so that I could view the information through the existing window at the bottom of the telephone, as well as get to the other buttons that are not associated with the disk dialer.

When dialing a number on a disk, a pair of contacts opens (normally closed NC contacts, green-yellow wire). The number of openings (P) corresponds to the set digit, for example, when dialing “1” = --, “2” = ----, etc. When the finger reaches the stop, another pair of contacts closes, briefly (white-brown). Using these two pairs of contacts, you can program the dialing process.

The controller board is made taking into account the shape of the device and the location of the contact group under the tube.

Each contact under the button is switched by an optocoupler, the inclusion of which is controlled by the microcontroller.

The Power bank (in the photo in the black case) continues to work as a source, starting with a load of about 20mA, if it is less, it will go into sleep mode. Therefore, a reed switch was mounted near the lever, which, when lifting the tube, supplies power to the LED through resistance (not shown on the circuit diagram). The LED, as a load, should be used more powerful, a small one will not work. You can also power the circuit directly from the battery contacts, but then you need to set the microcontroller's power to a low voltage when fuse bits are flashed. The battery is powered by the controller board and mobile phone. Power bank is charged via USB cable. Even without going into sleep mode, the battery capacity to power the controller board and mobile phone is enough for two weeks of battery life.

You can mount a mobile phone headset into the handset, instead of the microphone and speaker capsules. But I went the other way and redid the handset with capsules and the 3.5mm audio jack. Connection: the base of the connector - on the yellow and white wires (“-” of the microphone (360Ω) and “-” of the speaker (340 Ω)); the second from the base of the ring - on brown (“+” microphone); the third from the base of the ring - to green (“+” speaker). The colors of the wires for each model of devices are different! Additional impedances were selected based on the resistance of the coils of the headset, microphone (2000Ω) and speaker (45 Ω). For other mobile phone models, the resistance should be different. Experiment with mobile phones that you have already said goodbye to, not the fact that they will survive after such manipulations!

In the scheme, you should add a node for making a call, because the regular electronic call of a mobile phone turned out to be not so colorful as in the old device and quiet! In my case, there were no extra conclusions on the microcontroller, so I had to refuse the electromechanical call, which I regretted later.

During operation, I found out that you still need to duplicate the disk dialer with the buttons. Since the disc will not work to write text, let's say send SMS during registration.

Controller Operation Algorithm

I will give only the algorithm (comments). The whole essence of the algorithm, in a cycle: enable, disable ports under certain conditions.

while (1)
{
1. Procedure for short-term pressing the “cancel call” button from the button under the handset (when the handset is off-hook, the contact is constantly closed).
2. If there is 0 on PA1 ( contact is closed, the receiver is off-hook), then go to the code below:
- Turn on PD4 (mobile phone wakes up from sleep mode);
- Turn off the PD4.
3. If there is 1 on PA1 (NO contact is open, the button is pressed, the call is canceled when an incoming call is received), then go to the code below:
- Start the button timer counter under the handset.
If the button contacts under the handset were open for less than 3.1 seconds, then follow the code below:
- Turn on PD2 (call cancellation for an incoming call);
- Turn off PD2;
- Zeroing the number, for a new set with an outgoing call.
If the contacts of the button under the handset were open for more than 3.1 seconds, then the code below:
- Resets the state of the contacts of the button under the handset to start the cycle again
- Resets the number for a new dialing with an outgoing call.
4. The procedure for polling PD0 and PD1 contacts:
- If there is 0 on PD1 (NO contact closed) and 1 on PD0 (NC contact open), then go to the code below:
- Counter of the dialed digit of the number (from 0 to 9);
- If there is 0 on PD0 (NC contact closed), then go to the code below;
- If there is 1 on PD1 (NO contact open), then go to the code below;
- The counter of the number of dialed digits (total 11: 87.XX.XXXXXXX).
5. The procedure for automatically switching to a second SIM card (to another telecom operator, depending on the prefix of the number code, 3rd and 4th digits):
- Highlight tens in the prefix p10 = n * 10;
- The allocation of units in the prefix p1 = n;
- Formation of a prefix for the condition below;
- If operator prefix No. 1 is switched to SIM1. In the next set, if the prefix is the same, switching to SIM1 will not happen
- Turn on PD3
- Turn off PD3
- If operator prefix No. 2 switches to SIM2. In the next set, if the prefix is the same, switching to SIM2 will not happen
- Turn on PD3
- Turn off PD3
6. The procedure for turning on the LED "switching to SIM1":
- so that the LED does not work in standby mode;
- switching.
7. Enable pins of PB and PD ports for buttons 0–9.
8. The procedure for calling the dialed number.
}

The fifth point for automatically switching to another SIM card, someone will not need it, and you can exclude it. The code is quite primitive (if {} else {} in an infinite loop), which is why it works stably.

When designing, try not to damage the housing by drilling and sawing using standard openings and slots. Surely the GSM standard will be completely out of date, there will be new communication standards that can be used by implementing it in the same retro case.

I want to warn those designers who want to repeat the assembly of a similar device that after that there is always a desire to disassemble and update the filling, at the sight of rare telephone sets. And yet, do not talk on such a device outdoors, eyewitnesses may think badly of you!

GSM telephone with disk dialer

Electronics

Controller Operation Algorithm

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