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Author Topic: Rebuilding an 80's Motorola 4500x 'transportable' phone  (Read 7147 times)
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A few years back i bought a very cheap Motorola 4500x mobile phone. It weight around 4kg, and the analog phone network has been shut down long time ago.



Today i started to dismantle the phone. I want to replace its guts with a modern GSM module. Theres plenty of space, that's for sure.

Interesting facts:
- runs on 9v
- 12v battery pack, 4Ah, dead.
- undefined car charging connector , looks like a loop8 euro connector, but it is 12v and the plug is directional (positive pin is male)
- 1984 SMT components (!)

The plan.
- replace handset pcb with atmega328 to handle UI and input.
- keep existing keypad and 10-digit led display
- remove the contents of the slave transponder module, replace with Efcom pro GSM module (i2c)
- use the curly wire to feed power, i2c and microphone/speaker wires
- use pwm to drive the ringtone/touch tone speaker.

I have already a working cell phone on a breakboard. Project sounds feasible!

A few pics to wet your apetite (i apologize in advance for the big images, i'm on a tablet here)


* image.jpg (243.36 KB, 768x1024 - viewed 92 times.)

* image.jpg (214 KB, 768x1024 - viewed 86 times.)
« Last Edit: December 22, 2013, 11:07:23 am by RobvdVeer » Logged

Rob
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Some progress to show!

- I've successfully interfaced with the Sim900 module
- I've deciphered the keypad matrix
- I've resoldered a big bunch of wires due to a broken flat cable
- In the process I wrecked a part made of unobtainium (small 5 digit 7-segment lcd)
- Did a lot of research on parts and workings

Anyway, here's a small video of my working keypad.

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Cool project!
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Rob Tillaart

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I got a big deal of the firmware working already, i'm waiting on the amplifier ic's to arrive, the sim900 doesn't have enough power to drive the ear speaker.

Incoming and outgoing calls are working, and my design on cable reuse is also cool. Today i installed a massive 12v 1800mAh battery to power the beast. I'm expecting standby times of 2 months. Yes it has to stay heavy, right?

Today i blew a 5 digit led segment which is bad, because they are made from unobtainium. On the bright side, that opens up new possibilities for the User Interface. I'm now investigating the option to install a Nokia 5110 graphics display in the handset. Too bad there are no 40mm x 17mm OLED displays on ebay.
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can you not use a 8 digit (7seg) display and cover 3 of them?

The only time I saw unobtainium was in a TV documentary of rare earth metals smiley-wink

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Rob Tillaart

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can you not use a 8 digit (7seg) display and cover 3 of them?
Point me to any 8digit 7seg display 2cm width? These 2 5digit display go 4.2cm edge to edge with no room to spare. Certainly i didn't find a 7seg display that small.
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Picture of the new wiring starting to take shape. This is all 1.27 pitch through-hole, i really have to be careful not to make a short. Original solder is rock hard, really need to put some power into it. But heat up the board too much and the holes fall apart. today's pcb is much stronger. I use a tin sucker to remove the old solder before making a new connection.



Once this is all connected up, i'll share my stuff on the sketch.
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Not much progress. I'm waiting on some parts to arrive from China. I've ordered an amplifier ic to get some gain on the ringtone speaker, and i might need a little boost on the receiver as well.

I also researched a solution for the power circuit. I'm planning to do a so called Soft latch power switch, driven by the arduino. That means button to turn on, then same button to request a power down. Here's the diagram of something similar.


http://www.instructables.com/id/Soft-Latch-Power-Switch-Ardweeny/

EDIT: as i posted on the instrutables page, the 100k pullup from D0 needs to be removed. I don't want a 12v (9 on the diagram) connected to my input line on the microprocessor! Instead, use he internal pullup, or tie it to a 5v line.

I have all the hardware to do this, but it's SMD.. I'm not sure how to prototype this on a breadboard or protoboard..
« Last Edit: December 30, 2013, 03:27:46 am by RobvdVeer » Logged

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Today I managed to get the power circuit working. I had some issues with getting the p-channel mosfet to do what i intended, but now it is working fine. On the movie you see a little PCB above the Arduino Pro Mini. This board is just a breakout board for a SMD SOT-23 n-channel mosfet, because I don't have a PTH variant lying about.

Here's the video.



Here's the diagram.

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The fun begins. As all components basically work separately, it is now time to integrate all the bits.

But first, i will need to design the graphical user interface. I got 132x32 monochrome pixels, and i don't want it to look like a Nokia.

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Things are going really well, i'm getting close to hardware completion. I'm just waiting for the final 1uF capacitors to solder the graphical lcd screen.

Some lessons learned:
- be careful what sketch you upload. I fried a 328p because i uploaded a sketch that caused a shortcut between and input and an output pin.
- use an ic socket to avoid desoldering hell if the above point happens. I was smart enough this time. Chip out, fix error, new chip in.
- make sure you order the right parts. And measure twice. I now got 5 nokia screens with no purpose.
- make sure you have a free pin or two to leave your options open for unforeseen features (like abattery level check).
- don't use stripboard in a tight space.
- if possible, order the pcb. Its more epensive, but it saves you from procreating up 5 times on soldering the wrong pins.

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Rob,
I have a similar phone (maybe the same, but I can't check until tomorrow) that I don't want.
If it's the same then I can send it to you to solve your 'unobtainium' problem.
At least I'll know it's going to a good home instead of landfill.
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That is a very nice offer indeed, but i'm afraid the shipping would be devastating to get it to the Netherlands. However, if it is the same model there are some mechanical parts i'm interested in. Perhaps shipping could be reasonable without the (dead) battery.
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Meanwhile, here's a little update:

- all parts are now connected
- the display works, but is very unstable. Sometime it just turns off
- i can make and receive calls
- after a few seconds of connection, the gsm module just turns itself off
- there is a loud hum on the speaker and mic lines, only when a call is active

So i change the follower cap from the 7805 from 0.1uF to 10uF and the display is more stable now, also i have not experienced any dropout. But the hum is still there. I also here a 'tick' about every second. I will need to investigate if my software has anything to do with that,
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That is a very nice offer indeed, but i'm afraid the shipping would be devastating to get it to the Netherlands. However, if it is the same model there are some mechanical parts i'm interested in. Perhaps shipping could be reasonable without the (dead) battery.
Sorry Rob. I dug it out and had a look at it and it's a Motorola 8000.  :-(
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