Instrumentalities


Here, I describe the first-cut of how current tracks dealing with the Instrument Cluster and its sensors are detached from the central electrics and connected by the network. That’s tracks 71 to 126 inclusive; 4 sheets of schematic.

J-InstAux is the Instruments Auxiliary node that, in effect, is the network interface to the instrument cluster and a few other bits and pieces. The cluster connects to the car by a single, 28-pin connector.Instrument Cluster

J-InstAux proxies the majority of signals from sensors connected to other nodes in the car. The network isn’t however capable of easily transmitting some information because it either changes too rapidly or because the signal is too complex to reconstruct easily. The “cheat” is to simply pass the signal through J-InstAux from the original sensor.

Thus, the ignition pulses from the coil are wired, almost as per factory, to the tachometer in the instrument cluster, from the coil, making a transit through J-InstAux. Passing such signals through leaves the door open to innovation that could make the signal easier to pass over the network.

J-Front connects, on this sheet, to the coolant level sensor G32, the temperature sensor for the instrument cluster G2 (which has a different profile to the one for Digifant), the 0.3 bar oil pressure switch F22 and the 1.8 bar oil pressure switch. The data are made available on the network and J-InstAux proxies the signals for the instrument cluster.

The instrument cluster is pre-wired with 2 “spare” LED positions; used in other models. The sheet above shows them as “K” with J-InstAux potentially driving them via pins 20 and 22 on the instrument cluster. Useful information could be communicated!

85-98 Instrument ClusterTracks 85 to 98 of the networked instrument cluster shows the vehicle speed signal output obtained from G54 within the instrument cluster. The signal is usually available in such cars so that the radio can adequately increase the noise level as the car goes faster.

J-InstAux’s LINbus interface is also shown.

Moving right along:99-112 Instrument Cluster with MFA switchThis sheet shows tracks 99 to 112, representing the MFA (Multi Function Accessory) — or trip computer — and its controls on the steering column wiper stalk.  G55 is the simple device that monitors engine speed, load (via a vacuum sensor) and distance to display average speed, fuel consumption and travel times. It also displays the time of day, ambient air temperature and oil temperature.

J-DC monitors the MFA controls, provides their status on the network and J-InstAux proxies the signals accordingly. It sounds so easy, doesn’t it?113-126 MFA and brake sensorsThis is how the additional MFA sensors connect into the network. J-Front steps up to the line again and watches oil temperature G8 and ambient air temperature G17.

J-DC watches the handbrake F9 while J-Central, due to its proximity to the reservoir, monitors the brake fluid level warning switch F34.

J-InstAux is given the task of operating K7, the indicator lamp for handbrake and brake fluid level warnings.

That’s it. We’re almost there.

Nearly half-way through the standard vehicle electrics. 🙂

There are more sheets dealing with airconditioning, central locking, electric mirrors, etc.

Untangling the cables is being done on other pages. A corresponding database is being built offline, to eventually build up wiring diagrams to supersede the ones based on “painting  over” standard ones.

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