Lyon Retro Telephone With Dial Plate Convert to DECT Telephone Using Arduino and an Old DECT Phone

This instructable shows you a possibility to convert an old phone with dial plate into a phone connecting via DECT.

For my project I decided to use an Lyon Phone, Type DFeAp 330 of the German Federal Post Office of the year 1981. In Germany it is no problem to buy this phone on 'ebay Kleinanzeiger' for around 30 to 40 €.

But I think you can use every other phone with a dial plate. You only have to adapt the circuit board.

Because there was no DECT module you can use with an arduino (I didn't found anyone) I used the board of a DECT phone. Signals like pick up the phone, dialling and hang up the phone were converted by the arduino and send to the DECT board.

I will show you how I convert this old Lyon telephone into a DECT phone.

Here is the list of my requirements:

• the phone should be have a function like an old phone
• signal of free line when picking up the phone
• dial only when phone is picked up
• using the dial plate for dialling
• using the signal of the fork for start / end a call
• using the bell for ringing
• connecting the phone to a fritzBox (or another DECT station) via DECT
• using an automatic function following the steps of the DECT phone for connecting to a basis

Material:

1. An old telephone with a dial plate. I use the 'Lyon Phone, Type DFeAp 330' of the German Federal Post Office you can buy on ebay.
2. The board of a DECT phone. I decided to use 'Philips, Model XL 495' I also found on ebay. The advantage of this phone is its board. The contact areas on the circuit board for the buttons are quite large. So it is easy to solder a cable on the board. In a further project I used another DECT phone. It also worked, but soldering was very hard because of the very fine contact areas
3. Strip grid board. 38 mm x 45 mm. For the microphone of the handset.
4. For the circuit:
5. Strip grid board. 105 mm x 138 mm. The stripes must run in the longitudinal direction (138 mm). Raster dimension 2.54 mm.
6. Silver wire for the wire bridges
7. 10 x Resistant, 191 Ohm, 0.25 Watt
8. 1 x Resistant, 1 kOhm, 0.25 Watt
9. 1 x IC socket 8 pins
10. 2 x IC socket 16 pins
11. 2 x female connector, 20pins, raster dimension 2.54 mm, 1 row, straight
12. 4 x male connector, 1 pin
13. 1x Voltage regulator 20 W, DC/DC converter, XL6019
14. 1x ESP32 NodeMCU Module, 38 pins
15. 2 x IC LTV 846 (4 x optocoupler)
16. 1 x IC LTV 827 (2 x optocoupler)
17. 1 x LPT 80 (phototransistor, NPN)
18. 1 x transistor BC547
19. Battery holder (for 2 rechargeable batteries, AAA, 1.2V)
20. Micro USB 2.0 cable angled 90 degrees
21. Power supply unit, 5V, USB connection
22. If you have a crimping pliers you can use these connectors. Otherwise you can solder the cable direct on the board instead of using these connectors.
23. 1 x 4 pin connector male
24. 1 x 4 pin connector female
25. 2 x male connector, 5 pins, raster dimension 2.54 mm, 1 row, straight
26. 2 x female connector, 5 pins, raster dimension 2.54 mm, 1 row, straight
27. 2 x male connector, 2 pins, raster dimension 2.54 mm, 1 row, straight
28. 2 x female connector, 2 pins, raster dimension 2.54 mm, 1 row, straight
29. stranded wire, when possible in different colours
30. 10 x cable ties
31. Heat shrink tubing
32. double-sided adhesive tape
33. Insulating tape

Tools:

1. Cross-head screwdriver
2. Slotted screwdriver
3. Soldering Station (and also soldering tin)
4. tweezers
5. Side cutters
6. Cutter knife
7. crimping pliers (Please see 4.q. above)

The circuit has three parts.

On the left side you see the elements of the Lyon phone:

• bell
• switch of the phone fork (I don't know if this is really the correct translation. In Germany we call it 'Telefongabel'. I mean the button which changed his state if the phone is picked or hanged up. I will use the name phone fork. If someone knows the right word, please let me know!)
• dial plate

In the middle you see the circuit board:

• The circuit is constructed round an Arduino ESP32 NodeMCU. The main job of this ESP32 is to convert signals coming from the fork or dial plate into signals for the DECT and also to convert signals form the DECT (only the LED signal for an incoming call) into a signal for the Lyon phone.
• For the bell we need a higher voltage than 5V, so a DC-DC-Converter is used to generate 20V for the bell
• The bell was connected to the arduino via transistor. A signal (HIGH) on the basis of this transistor will put the second connection of the bell to ground.

All inputs of the arduino were programmed as inputs with an internal pull up resistant.

• The switch of the fork sends a LOW signal whenever the phone is hanged up.
• The dial plate have four cables (yellow, green, brown, white). Two cables are used for the impulse while dialling (yellow and green). The other two cables (brown, white) signal the dialling process. When dialling the brown cable send a LOW signal, otherwise a HIGH signal. When dialling impulses were generated. Each impulse means a change from HIGH to LOW. The number of pulses is the number you dialled. These signals are send by the yellow cable.
• The matrix of the buttons of the DECT phone (see further step) is controlled by using optocoupler. The Philips Model XL 495 has a 5 x 5 matrix. So we have 5 cables for each port. Port means the horizontal and the vertical direction of the matrix field.
• The phototransistor detects the incoming signal (LED) an sends a LOW signal whenever the LED is on.

On the right side of the plan you see the DECT phone.

Let's start building the phone!

NOTE: The DECT phone can be connected to the original basis or another basis like a fritzBox. Therefore, you have to do some settings in the menu. Please see the instruction of your phone. The arduino code includes a sequence of keystrokes for automated connection to a original basis and to a fritzBox. Please try out to connect the phone to the basis you want to use later. Write down every step you have to do like: 'menu', 'down', 'down', 'menu', 'menu', '0', '0' ,'0', '0', 'menu'.... If the included sequence in my code isn't correct you can change this easily. But we have to remove the buttons of the phone in the next steps so it will be much more difficult to press any keys and to try out the keystrokes.

We start preparing the DECT phone. We need the board of this phone. First of all remove the rechargeable batteries of the phone (we need them later!). Remove the two screws on the bottom of the phone. Open the cover of the phone. Now you will see the board. You will find 4 cables connected to the two speakers. You can de-solder them now (I did this a little bit later, so you will still see this cables in following pictures). In the middle of the board on the right and on the left side are two screws. Remove this screws. Now you can put of the board. There is a white foil on the circuit board. Remove this foil. Now you can see the contact areas of the push buttons. Each contact area consists of an inner point and a surrounding ring. Every time a button will be pressed, the point and the ring will be connected like a closed switch. Points and rings forms a matrix. In the following step I will show you how the matrix of this phone is constructed.

The first picture is a representation of the keyboard matrix. A closed switch establishes a connection from an output of Port A to an input of Port B. By the combination of the output of Port A and the input of Port B can be calculated which button was pressed. The picture with the colourful circles shows the connect areas of each push button. Circles with the same colour are connected. I defined numbers for each colour and assigned them to the areas. You will see the result in the next picture. You can see the buttons and the numbers. For each button the lower number was on the left side. In the last step I sorted the switches according to the left number. Now you can realise the matrix of the buttons. In the next step we solder cables to the areas so that is possible to control the buttons by an arduino. With the arduino we generate connections from port A to port B.

Because of the matrix for the buttons we don't need two cables for each button. We only need ten cables for controlling all buttons. Five Cables for numbers 0 to 4 of our matrix and five cables for the numbers 5 to 9 of our matrix (as you can see in the picture of the matrix in the previous step). These numbers are not the numbers of the buttons! In the photo of the board with the soldered cables you can see the five cable on the upper part of the board (0 to 4) and the five cable on the middle part of the board 5 to 9). I tried to use the inner point for soldering as often as possible. Be careful that the point and the ring were not connected after soldering.

The Lyon phon has a good old electromechanical bell. We want to use this bell instead of an electronic generated sound.Therefore it is necessary to detect an incoming call. The Philips Model XL 495 has an LED blinking whenever the phone is ringing. We use this LED to detect an incoming call. for this we need a phototransistor placed over the LED. That isn't very difficult. Put a little bit of a double-sided adhesive tape round the phototransistor like you see in the photo. Around the LCD display of the DECT phone there is a rubber frame. In the rubber frame there is a cut-out for the LED. This will be the place were the phototransistor is put in. On one photo you can see the phototransistor positioned direct in front of the LED. Please solder two cables to the connections of the phototransistor. The phototransistor has two connections - a large one and a short one. The large one is the CONNECTOR, the short one the EMITTER. I used a yellow cable for the connector. I fixed the phototransistor with insulating tape.

The Lyon phone has four screw at the bottom. Please remove all four screws and open the phone. You will see the board with some electronic pieces, connectors and the button for 'phone fork'. We need some pieces of this board, so we have to remove them from board.

Please disconnect all cables. The button for the phone fork has to screws. Please remove these two screws. Now you can remove the board. Please solder out the button of the fork and some also some connectors (we will need seven connectors later). And we also need the two connectors near the phone fork labels Z1 and Z2.

The microphone of our Lyon telephone will not work with the DECT. So we will use the microphone of the Philips phone. Please remove the microphone of the board.

Now we can change the microphone of the handset. Open the handset on the side of the microphone. Remove the microphone by disconnecting the cables.

Because of the small size of our 'new' microphone we need a little circuit board to fix the microphone in the handset.

Please cut a circuit board to size as you see in the pictures. Then solder the microphone and the pins (see previous step) on the board. Place the board with the microphone in the handset and connect the cables. Close the handset.

We have to connect the handset to the DECT board later. So, you can now solder cables to the soldering pins of the microphone and to the soldering pins of the speaker.

Now we will build the circuit board.

Please cut the board in size as you see in the picture. It is important that the number of holes is correct.

NOTE: Try if you can place the board to the Lyon phone in the way the old board was.

After that, we will have to set some interruptions. Therefore I have two plans as you see in the pictures. On shows the interruptions looking from the mounting side and the other shows the interruption looking from the soldering side. I first marked the interruption. Then I use a drill of 3.2 mm to make the interruptions.

NOTE: Please use the plan for the interruptions - not the photo. The photo will not show all interruptions!

We starts soldering with the most flattest pieces. So we begin to solder the wire bridges. There is also a special plan.

Next we solder the resistants. Only the resistant on the right side is 1 kOhm, all other resistants are 191 Ohm.

Then we solder the sockets for our IC (optocoupler).

After that we solder the two 20pin female connectors. NOTE that these are 20pin connectors. Our EPS32 only has 19 pins on each side. Be sure that there are three rows between the connector and the upper side of the board! Solder also the other connectors as you see in the picture. There are six connectors we had from the Lyon board, one more we need a little bit later! Maybe you need to enlarge the holes on the board a bit by using a drill of 1 mm. On my board I forget the 2 pin connector for the phototransistor and for the power of the DECT phone. You can solder them now, too.

Now we solder the DC-DC converter on our board. The converter I used had no pins. So the first step is to solder pins to this converter. This is much easier using a breadboard as you see in the photos. After the pins were soldered on the converter board, place it on the circuit board and solder the pins.

There is one transistor we had to solder on our board.

Now we have to prepare the fork button. The button has a little pin of plastic at the bottom. With this pin, we can't place the button on our board. So please remove this little pin. Place this fork button on the circuit board and solder it.

The last step is to put the ICs into the sockets. Look for pin number 1! Look at my photos were pin number 1 of each IC has to be. Then put the arduino into the female connector. Remember that we used a 20pin female connector on each side but that the arduino only has 19 pins. So start at the upper side of the board! Look at the photos!

We finished the circuit board - nearly!

I thought a long time about how to place and fix the DECT board on the circuit board or in the case of the Lyon telephone. My daughter was the one who had the idea with the connector.

I Think there is a cable of the Lyon phone we don't need. But we need the connector. Remove the connector from the cable and solder it on the DECT board like you see on the photo. Solder the last connector on the circuit board. Now we can fix the DECT board on the circuit board using this connectors!

There is a little problem with the power of the DECT phone. I tried to connect the phone to the 3.3V output of the arduino. You can power on the phone, but when dialling the power goes down because of the higher current. So I used the rechargeable batteries.

Solder cables to POW+, POW-, CHG+ and CHG-. For me it was easier to remove the contacts for the batteries and to cut of the contacts for charging a little bit.

Place the board to the ground plate of the Lyon phone.

Place the DECT phone onto the circuit board.

Place the battery holder to the ground plate of the Lyon phone and fix it with double-sided adhesive tape. Solder the cables coming from BAT+ and BAT- to the battery holder.

If you don't have a crimping pliers please solder the cables directly to the board respectively direct together. Otherwise attach the connectors to the cables:

• the five pin female connectors to the cables for the matrix of the DECT phone (two times)
• the two pin female connectors to the power cables coming from CHG* and CHG-
• the five pin female connectors to the cables of the phototransistor
• the four pin male connector to the cables coming from the handset
• the four pin female connector to the cables coming from the soldering pins of the microphone and the speaker.

Connect the cables to the connectors on the board respectively direct together (cables from the handset).

Please download the code Lyon_v0_91_eng.ino for the arduino on github. Upload the code to the arduino.

If this is your first project with an arduino please follow the instructions on https://www.arduino.cc/en/Guide.

If this is your first project with an ESP32 you have to install the URL

https://dl.espressif.com/dl/package_esp32_index.json

in your arduino IDE under file --> preferences --> settings --> Additional Board Manager URLs:

Please choose ESP32 Dev Module under Tools --> Boards --> Board manager

Connect the arduino to your computer and upload the file.

For testing you can connect the arduino via USB to your computer. Using the serial monitor you can see some informations (like picking up, hanging up, dialling process, dialled number) and you can also send signals to the arduino to test the software and hardware. You will find the list of commands in the readme file on github, too.

“0" , "1", "2", "3", "4", "5", "6", "7", "8", "9"

 "h"     pick up

 "l"      hang up

 "m"    menu

 "s"      mute 

 "u"      up

 "d"      down 

If everything works fine connect the arduino with the micro USB 2.0 cable angled 90 degrees.

Screw the body of the phone back together!

Finished.

Connecting the phone to a basis or a fritzBox

This telephone followed the function of an old telephone. Means first you have to pick up phone, then you can dial.

But there is one more special function: the automated connection to a basis or a fritzBox. When the handset is hang up and you dial '9' a sequence of keystrokes will be send to the DECT phone correspondents the steps for conecting to a basis. If you dial "0" a sequence of keystrokes will be send to the DECT phone correspondents the steps for conecting to a fritzbox. Maybe you have to dial '0' first and then '9' or the other way round. The menue of the DECT phone will be changed dependet on the basis (original phone basis or fritz box).

NOTE: If there is a problem with the functions of you phone and your fritzBox please check following settings in your fritzBox (I only had a German fritzBox, maybe there a other words on English).

phone --> DECT --> basis station --> troubleshooting

mark following points:

• Troubleshooting for cordless phones that are not GAP compatible
• Support for CAT-iq 2.0 compatible devices active

If you use another DECT basis than the original one or a fritzBox you can change the sequence for automated connection easily in the code under 'void linkBasis ()' or 'void linkFritz ()'. Hope you wrote down your sequence of keystrokes for connecting (see step 2).

matrixCalc("m") means: press 'menu'

matrixCalc("d") means: press 'down'

matrixCalc("u") means: press 'up'

matrixCalc("h") means: press 'pick up'

matrixCalc("l") means: press 'hang up'

matrixCalc("s") means: press 'mute'

matrixCalc("0"): press '0' (and all other numbers of course)

Have fun making them!