Memory dump of ECU

[b3lha]

Originally Posted by Trevor

Phil the input described/shown here fronting an OP AMP, is exactly in accordance with the issue I raised earlier in this thread, i.e.

“Or is your input impedance/loading too low i.e. too sensitive. A higher relative loading would pull down the output/input signal voltage. This could be where the Subaru OEM monitor differs. The fact that you indicate that a zero voltage is not being recorded, points in this direction.

The lower the monitor input impedance/resistance; the greater the signal current; lower the voltage (Dependent on output capacity) and greater the immunity to noise. In all respects the transmitted signal is more robust, a worthwhile feature.

In other words, the existing signal could be overloading your gear. Think of the affect of overloading the input of an audio amp.”

“As you have no data to make calculations, trial and error will be the order of the day, as will be a rather crude approach to the problem.

The simple approach is to add a resistor across the monitor input as a shunt. Measure the resistance at present existing across the input and as first trial, connect a resistor of say four times this value in parallel. You will appreciate that reducing the value of this resistor, will further reduce sensitivity and increase the demand for current.

I would anticipate that a small carbon resistor should suffice in respect wattage. There will be problems of a mechanical nature in arranging connections and you will probably have to make up an in and out plug socket arrangement.”

The sophisticated approach towards input impedance correction, which I did not suggest for good reason, is to add a series and a parallel input network. The circuit shown goes further by isolating the input loading via a low gain amp.

You should also notice that the circuit, as would be expected, incorporates a stand alone IC voltage regulator, cost near zero. Reference has been made regarding the possible influence of supply voltage in respect of problems. It would be strange indeed if all of the items in use, were not likewise protected, and on this basis I would discount this as a likely issue.

All the best with your project. Thankfully you now have many chewing with you. Trevor.

Sorry Trev, you've lost me!
When I first mentioned a resistor I was thinking to put it in series in order to reduce the voltage between the receiver input and ground.
I can see how putting a resistor in parallel will reduce the current flow through the receiver circuit but I don't understand how the amount of current relates to a digital circuit where the signalling is in terms of presence, or absence, of current.
With due respect to your expertise in this area, I am planning to try Calum's solution because it has been shown to work on a JECS Nissan ECU and therefore it should work on a JECS Subaru ECU.
Phil.