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Which means "Evil Twin". Lets see your projects where you change boring into fun or create the fun from scratch.
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PostPosted: Sun Nov 01, 2015 6:59 am 
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I had it in my head the haltech thing was a simulator not a sink :oops:

You're going to need an O2 signal too right?....can you just give it 0.5V and it's happy?


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PostPosted: Sun Nov 01, 2015 12:51 pm 
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These ECU's had WBO2 sensors upstream of the cats and NB Lambda's downstream, so I'm "hoping" I can use the same sensors for both the OEM ECU's and the EngineLab. I don't know what sort of input impedance the EngineLab has, but hopefully it won't load the circuits down too much.


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PostPosted: Sun Nov 01, 2015 1:20 pm 
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cribbj wrote:
These ECU's had WBO2 sensors upstream of the cats and NB Lambda's downstream, so I'm "hoping" I can use the same sensors for both the OEM ECU's and the EngineLab. I don't know what sort of input impedance the EngineLab has, but hopefully it won't load the circuits down too much.


My worry would be getting the mixture where the old ECU doesn't get angry......


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PostPosted: Sun Nov 01, 2015 1:28 pm 
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You can't really piggyback wideband sensors.

A wideband sensor has 4 key parts: heater, pump, nernst cell, and cal resistor.

Heater is connected to +batt and a low-side driver, sometimes with a current-sensing shunt resistor. Only one ECU can drive the heater, and it has to be the same ECU that drives the sensor since the sensor temperature is important for heater control and for widebands it's usually derived from the sensing element. With the sensor disconnected the ECU will probably throw a fault immediately and go open-loop.

The other 3 sensing elements share 4 wires (Nernst, Cal, Pump, Ground). Nernst is the narrowband element, Pump is an oxygen pump, and Cal is a resistor.

The pump is actively driven (the current in the pump required to bring the Nernst to stoich is the raw sensor reading) by a hardware control loop in the CJ125/L9780/etc. to keep the Nernst at a target voltage (roughly 0.45 v). Usually a voltage DAC is used to drive the pump. You don't really want the two pump pins connected together since their DACs wil fight and current readings will be way off.

Nernst should be okay, but the virtual ground is shared with the pump cell and it can also be driven by a DAC to increase the voltage range of the pump (so if you are limited to 0-5v, you can drive the pump to -4v by driving the ground to +4v and still read the Nernst at 4.45v). Nernst should use an op amp though so it might be okay.

Don't piggyback widebands!

For NB's, some controllers use an ASIC like the LM9040 (which is basically a differential amp with bias on the output). But, you can read a NB sensor by connecting the ground to a low voltage source (like 1.5v or 2.5v) and reading both the voltage and sensor to get a +-1.5v sensing range with 0-5v ADCs and only discrete components. If this is done, then you can't share the sensor since the ground is actively driven and 2.5v ground is out of the common-mode range of the L9040.

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PostPosted: Sun Nov 01, 2015 1:46 pm 
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To simulate a sensor (WB or NB, assuming you had it electrically worked out) the upstream sensor probably expects to see an oscillating signal around stoich (it will very rarely deviate from stoich, with a NB it will go open-loop whenever it isn't stoich).

For the downstream, it will also look for oscillations, and it will compare the frequency of oscillations to the frequency from the upstream to judge the catalyst oxygen storage capacity (and catalyst health).

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"Any sufficiently advanced technology is indistinguishable from magic" ~Arthur C. Clarke


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PostPosted: Sun Nov 01, 2015 3:53 pm 
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Well, as you can see, I haven't completely thought this through yet :) OK, so sharing of the WBO2's obviously isn't going to work very well...... so I'll need to get some new bungs put into the exhaust collector.

I'm guessing some of the other sensors probably aren't going to be that happy being shared either, like CLT, AIT, etc.

The ones that I really do want to share, however, are the crank & cam triggers. I would think these wouldn't be too fussy about being connected to multiple ECU's, whether they're inductive pickups or Hall's?


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PostPosted: Sun Nov 01, 2015 4:02 pm 
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It depends on the circuit used to read the sensor.

For most thermistors (and RTDs too), they have a low-resistance pull up in the ECU and it measures the voltage across a resistor voltage divider, with the sensor making up part of the divider. RTDs are usually arranged to form a bridge. One of the ECUs would need its pull resistance removed (or use an extremely high value, usually 1M is used to allow truly open circuit detection still) to share.

For thermocouples you can split them fairly easily as long as you use thermocouple wire everywhere and neither of the circuits grounds the thermocouple (both need truly differential inputs). Unfortunately thermocouples are not used here.

For pressure sensors and TPS you should be fine sharing.

Hall-effect sensors should split well, BUT there will be a pull-up resistor in both ECUs so the sensor will have to sink twice the current (probably not an issue) and some ECUs use higher voltages (8v or 12v) for the Hall sensors so that could conflict.

For VR sensors, usually one side is grounded and the ECU often has a load resistor connected across the VR sensor to bring the voltage down to a manageable level. Fortunately they don't care about current or voltage, only zero-crossings of a sine wave, so you should be able to connect a VR sensor directly to one ECU and split it to the other with an isolation amplifier (I've used an oscilloscope differential probe for this).

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