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Content 4/4

I bought a second hand FIAT Seicento, then I discovered there was installed a non working car alarm system (Gemini 7300).

Alarm was a too old model to get support or repair service. No available replacement boards (or new units) on internet.

I would like to add a remote control for door openinig, I could buy new one from Amazon or Ebay but I'm too lazy to replace all wirings and connectors.....

FIAT models (such Seicento or Cinquecento) are supplied with automatic door control unit (additional remote control was optional and expensive), so I need few electronics to apply remote control, then I already have wirings from Gemini 7300.

What about making a new board to fit inside Gemini 7300 enclosure re-using some components and connectors?

So I made a new board with basic functions (door open/close, cockpit led, blinking indicators and fuel pump control) using PIC microcontroller, wireless receiver with integrated decoder and few components.


As RF receiver I used Aurel RX-4MHCS (4 channel RF receiver with integrated rolling-code decoder) for following reasons:

  • easy to find
  • enough cheap
  • rolling-code to increase security
  • nice handheld transmitter available (see pictures, regardless 1, 2, or 3 channels version)

About transmitter we can find two models (I used only first channel).


Microcontroller just needs to manage receiver output to command doors control unit, check if doors closing command correctly worked (using feedback terminal), blink led when doors are closed.

When pressing remote control button PIC gets output from RF receiver, commands door control unit to open or close doors (depending on signals on input terminals), then checks if configuration has correctly changed.

When opening door you'll see long blink of indicator lights.

When closing door you'll see long blink and short blink. (then cockpit led starts blinking).

If something wrong you'll se 3 short blinks.


Door feature (open/close) is always active.

I used Gemini 7300 key-switch toenable/disable fuel pump (fuel relay supplies power only if enabled and ignition key is ON) but I discovered too late fuel pump wirings were not connected.

When you buy remote control you have to follow pairing instructions on RX-4MHCS, depending RX-4MHCS firmware.

On links you can find additional documentation such wirings and microcontroller firmware.


BTW: first PCB was designed for different PIC microcontroller, that's why there is soldered wire. I updated PCB gerbers for PIC18F1330.

Mar 25,2020
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