[cdvs]

Phil, I've been holding back on this whole connector issue. You have made a tremendous effort which I respect greatly. So, I didn't want to say that a good chunk of this work probably wasn't necessary. I especially didn't want to say this without having proved it myself. I haven't done this. I've been preoccupied with other things and while I find this very interesting I just can't give it very much of my time. However, it now appears that perhaps if I share what I think I know, it will be helpful in achieving your goals. Specifically by making it easier for others to join in the fun.

I do have historical experience with RS232 DTE (data terminal equipment) and my suggestions are based on this.

1. Unless there is a requirement for one device to be powered by the other, no positive voltage connection is required or recommended. This is not the case here, so deleting the positive connection eliminates one perceived incompatibility.

2. The data line standard for modern computer equipment is +3 to +12 volts to signal 'space' or zero and 0 volts to signal 'mark' or one. Both the ECU and your laptop are 'modern' computers and should operate fine as long as the signal voltages are in this range. It doesn't(shouldn't) matter if they are different. There is every reason to expect that the Subaru Select Monitor is no different in this regard.

3. We are left with the infamous 3 wire connector. Receive on one end connected to transmit on the other (times 2) and ground. No special conversion electronics required.

Remember, I haven't tested this and free advice is worth what you paid for it.

Charl