Hardware to software: reverse enineering a ICU from a 1991 Honda
Hardware to Software⌗
So as some may know there are these ICU(integrated control unit)s that were used in many diffent types of Honda’s cars from 1988-1991. These modules are responsible for controlling a vast variety of systems in the car such as:
- Turn signals
- Daytime running lights
- Seatbelt warnings
- Status indicators
- etc
Many of the cars of those years on the road today have or will soon expirence some kind of malfunction or failure of the I.C.U. module. They are known for causing strange and often hard to diagnose issues.
With all that said my the goal is to build a drop in replacement unit that will minimize the number of parts needed, reduce the relicance on analog control via capacitors and relay’s and provide an alternative to buying a expensive replacement unit from Germany on Ebay(which I just did to have a second unit).
The Original Unit⌗
The OEM unit that I’m currently using is an older one manufatured by MITSUBA in Japan. The enclosure is a brown plastic injection molded box and it makes use of two diffent styles of connectors.
Both the existing connectors are…unquiue to say the least. Given the pin spacing and dimensions I have yet to find the name of them and haven’t even seen anywhere to buy connectors that look even semi simalar.
But, none the less I still decided to take messurements using a pair of digital calipers and build a 3D model.
The Next thing to take notice of is that there are many places on the PCB that are drilled but unpopulated by the standard through hole componets that we see on the edge of the board.
Variety of versions⌗
The ICU has actually been in use for all the 1988 CRX , Civics, Civic SI, Integras of certain years etc.
Because of this we have to be careful of missing features such as if DRL(daytime running lights) are a standard feature on a given model.
The Factory Schematics⌗
The facotry electronic schematics give a good overview in the form of a block diagram. It’s not ideal from the point of view of wanting to replicate the circuits exactly, but it’s good enough for emulating the same kind of functionality.
Building a new schematic⌗
First I started off by doodling down ideas for the circuit on some paper just as a sanity check.
From there I proceeded to build individual circuits in KiCad along with any nessisary schematic symbols needed + labels.