Quote:
Originally Posted by SVXdc
You can't try to measure resistance on a circuit that is powered. You could try measuring voltage -- on either the HU's SWC1 or SWC2 pin with respect to ground (test one SWC pin at a time). When the OESWC-RF module is not sending a command, or when nothing is connected, you'll probably see the HU outputting +5V. When the module sends a command, the voltage should drop to something between 0 and 5V (different value for each button).
But if the module is not detecting the HU, it likely won't even try sending commands to the HU
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Made some progress - I think I'm getting closer:
- HU is indeed responding to commands, although the unit is, well, not particularly fast, so very brief shorts to the ground (which are "Seek+" and "Mode" for SWC1 and SWC2 respectively) do not register at all.
- in the "auto-detection" mode, it looks like OESWC module in the beginning of each ~20-second cycle sends (very briefly) voltage sequences to SWC1/SWC2 pins. Even my friend's pro-level multimeter was not quick enough, and I don't think I'm ready to invest in an oscilloscope
- According to Toyota specs, the normal voltage between SWC1 and ground, and between SWC2 and ground should be in the 4.5-5.5 volts range. The voltage on both SWC1 and SWC2 pins is 3.4 volts, so I tapped 5 volts from an old cell phone USB charger to both SWC pins (disconnecting them from the HU first, just in case).
The good news: the module immediately went into the "detected" phase, so it does look like it expects a specific voltage on SWC pins.
The not so good news is that apparently the detected stereo type was not correct - any button press (doesn't matter if it's short or long) would send what looks like a digital sequence to the SWC1 pin, and nothing to the SWC2 pin.
My next steps are:
1) Looks like Nissan's stereos have 3.3 volts on SWC pins from the HU - I'm trying to get hold of a high-res picture of their Nissan-specific harness to see what two pins on the OESWC connector are wired for the SWCs, there's a chance those are different pins and maybe it's just a question of using the right one;
2) try to get a hold of either a variable voltage power supply, or just a couple of potentiometers to simulate different voltages and see if I strike gold - my friend's Solara didn't even have pins for SWCs, so there's nothing I could measure.
There's still a chance that the HU won't understand a single command OESWC will generate no matter what mode I'll be able to trick it into; in this case, it's cheaper for me (both cost-wise and time-wise) to just replace the HU - the OEM is not THAT great