Trying to communicate with 1226865 ECM

American Delco GM ECUs and PCMs, ALDL, OBD 1.5.
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Re: Trying to communicate with 1226865 ECM

Postby j_ds_au » Fri Sep 27, 2019 4:14 am

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!

ND

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.

Joe.

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Re: Trying to communicate with 1226865 ECM

Postby ndndndnd » Sun Sep 29, 2019 8:32 am

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?

Thanks!

ND

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Joined: Sun Jan 25, 2015 4:21 pm
Location: Sydney

Re: Trying to communicate with 1226865 ECM

Postby j_ds_au » Mon Sep 30, 2019 4:29 am

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?

Thanks!

ND

Hi ND,

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.

Joe.

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