American Delco GM ECUs and PCMs, ALDL, OBD 1.5.
ndndndnd wrote:Do I need another transistor circuit to invert the signal? I thought the 'Q1' transistor (2N3904) in the WinALDL circuit already inverted the signal? I was investigating inverting the signal so I could omit the transistor circuit and reduce the number of variables...
I guess what I'm getting down to is: does anyone know if this circuit should be working, even through the FT232BL chip?
Thanks for your continuing help guys!
The purpose of the existing transistor is as a buffer and level converter. The fact that it also inverts is a nuisance in this case.
The circuit is fine (indeed, looks quite good) if you're driving an FT232RL, because you can enable a further inversion within the chip. But it cannot work with an FT232BL without an extra transistor (and two 10k resistors) to correct the signal polarity.
ndndndnd wrote:Ah, ok. This almost sounds like progress!
So, ummm, how do I wire in the extra transistor and where do the extra two 10k resistors go? Can I just use another 2N3904?
Yes, a 2N3904 is fine. Ground the emitter; connect one resistor in series with the base, the other end connecting to the collector of the first transistor (disconnect the FT232BL); connect the other resistor as a pull-up to +5V for the collector, which then feeds the FT232BL.
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