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It's evolving: Aiphone video intercom

Modifying an old video intercom to bring it up to the 21st century.

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A small project aiming to change a few of the basic specification of an old video intercom and if possible, try adding to it new functionalities to make it more like a proper modern intercom.
Ultimately, I wish to add WiFi connectivity to it so I could integrate it to my modest home automation system.

When I went for a preliminary inspection for the apartment I'm living in now, two things really struck me.
- First, the fact there was no door between the entrance area and the bathroom (when you get in, in front of you you can see the bathroom and the shower unit).
- Next, that old video intercom with its tiny screen and old fashion ringtone. 

I took care of the "no door situation" right after I moved in: I simply made a door frame (that can be remove at any time) and built my own door. Now I want to do something about this intercom and especially I'm thinking of upgrading it so it can be an item that belongs to this century. 

My main ideas are:

  • change the screen for a bigger one
  • add an auto-recording function (SD card)
  • add a player function (to play recordings directly from the intercom)
  • add an auto-response system that includes an auto-opening option (for package delivery)
  • add a WiFi or Zigbee connectivity feature (to integrate it to my home automation)

I'm confident I will manage to implement the first three upgrades but ain't sure at all about the last two. Modifying the intercom so that it can be integrated to Home Assistant would be awesome but I'm septic that my skills are good enough to achieve this but I will still give it a try.

mainboard_XC1227.sch

Schematic of the circuit that connects to CN101 on the mainboard

sch - 31.39 kB - 07/06/2021 at 14:27

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  • So that's what it's for...

    Florian07/10/2021 at 03:02 0 comments

    Using LTspice XVII I simulated the part of the circuit of the display module I didn't understand what its purpose was. For the composite video signal source, I used the NTSC voltage source published here by Bordodynov

    And here is the simulation results:

    So it's look like this circuit is adding a small offset to the original signal, making it completely positive (no more signal falling under 0V). As I know nothing about video signal, I assume there is AC and DC coupling for video composite signal and that small module display works only with DC coupled signal?

    To help me understand better, I looked for some litterature and found those:

    From what I understood, the composite video signal coming out of the mainboard should be AC coupled and that small circuit in the display module does a DC restoration before feeding the composite signal to the LC749880T (Image controller LSI for LCD-TV).

  • Nothing when energized? Let's dig in

    Florian07/06/2021 at 14:25 0 comments

    To confirm the power voltage of the display module and so the power generated by the step-down DC-DC regulator (LM2736YMK), I plugged the intercom to main power and did some measurements with my multimeter. I mainly focus my attention on the area where the display module connects to the mainboard, which is the following:

    Unfortunately, despite the intercom being energized and being responsive when the front botton "通話/終話" was pressed, there was absolutely no voltage whatsoever in this area of the board. I thought something was wrong with my multimeter so I poked at the transformer and it's surrounding: my multimeter was working well. 

    So after this infructuous result, I decided to reverse-engineer the traces going to this CN101 connector and damn that was a lot of work! But it was totally worth it as I managed to figure out:

    • the mainboard provides 12V to the display module, which is generated from the video feed signal
    • the LM2736YMK on the display module does generate 3.3V (calculated from the datasheet)
    • the received video signal is FM modulated (demodulation IC is LA72910V from SANYO)
    • pin 5 of CN101 on the display module is connected to the brightness control potentiometer of the mainboard 

    For more details, here is an image of the schematic I created but you can find the corresponding Kicad file in the FILES section.

    My next course of action will be to simulate that circuit I didn't understand the purpose of and also see if I can connect that cheap 4.3" screen with double composite video input I bought quite a while ago. I hope it will be as easy as just connecting it to the mainboard video output to get it towork. 

  • More about that display module

    Florian06/27/2021 at 01:27 0 comments

    Let's see that display module in details: 

    it is labeled "TB10126 R" (frame top side), the TFT display itself is made my AUO and labeled "06B806Z84B227I026A0U00 8501". Those keyword returned nothing on Google so let's have a look on the back.

    A 10 pin connector CN101, to which only 6 connections are made. Also, 3 big ICs (one is under the ribbon cable) which are:

    From the SANYO image controller datasheet, one of its feature is ”CVBS, S-Video,YCbCr/YPbPr input" and a closer look at the input table shows 2 CVBS inputs, one S-Video input and one YCbCr/YPbPr input. As this controller is right next to the only connector on this display module, I traced all the pins connection with a multimeter and came up with the following schematic:

    To summarize:

    • pin 4, 6, 8 and 10 are GND
    • pin 9 is Vin (I assume 12V), which is step-down to 3.3V via a LM2736
    • pin 7 is composite video input, which goes through a... I don't know circuit and then to CVBS1 of SANYO LC749880T
    • pin 1, 2, 3 and 4 are unknown and are connected to respectively pin 2, 23, 22, 2 of the unknown IC

    Next time I will confirm the input voltage of this display module, the ouput voltage of the LM2736, simulate the circuit between the composite video input and CVBS1 to understand its function and maybe analyze the intercom mainboard's circuit to which this display module connects.

  • I got myself a new toy

    Florian06/22/2021 at 13:34 0 comments

    After a quick search on mercari and Yahoo Auction, I found someone selling an used video intercom unit with a door intercom at a decent price so I bought it.

    First things first , let's see what's inside!

    A transformer, 2 pcbs and a display module? The fact that the display is a modular unit by itself is a great news. If I can find a datasheet for it I would be able to easily identify its pinout and understand how it connects to the intercom mainboard. Which would greatly help me figure out if I can easily swap the display for a bigger one.

    Here are more photos of the pcbs: first the tiny one (seen on left)

    The mainboard one:

    And the same one, but this time back side:

    In my next log, I will have a closer look to the display module, try to find some information about it and figure out its pinout.

  • First, gathering information

    Florian06/16/2021 at 10:41 0 comments

    So what is it? 
    A video intercom model GAM-2MK made in 2008 by a Japanese company named Aiphone.

    A quick search on Google and here is the company site. From here, ダウンロード > 商品情報・データ・ソフトウェア and using the quick model search, we arrived to this page with all download available documents: profile sketch (DWG and DXF) and specification. No manual? Well with some help of Google again, here it is.

    From this few documents I didn't discover much:

    • the display is a 2.5inch TFT
    • this model can only be connected to a GAX system
    • its connection diagram is as follow (RA1/RA2 is the video feed, R3/R4 is the sound feed)

    Maybe I could find more information if I look for documents for the video entrance panel?
    Back to manufacturer site, a quick search with the word GAX and here is the video entrance panel. Unfortunately all there is a specification document and after reading it, nothing really useful in it.

    Well, guess I will simply look for an used video intercom that I can play with it at will. Can't really do that with the one installed in my apartment as I'm just renting the place and I don't want to risk damaging it.

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