New ALDL 2 transistor circuit (critique)

[Peter Gargano <peter@ntserver.techedge.com.au>]

I've had a few questions about the two transistor ALDL interface
circuit appearing on Andy Whittaker's web site. The page is:

 http://www.andywhittaker.com/ecu/aldl_hardware.htm

and the circuit, attributed to Sanjaya Vatuk is:

 http://www.andywhittaker.com/ecu/images/Simple_ALDL_Interface.gif

I'm sure this circuit will work on certain PCs. The problem
is that the voltage levels on pin 2/9 (RxD) vary between 0
and +12 Volts. Unfortunately, RS232 is not guaranteed to
work reliably at a lowest voltage level of 0. OTOH, most
laptops seem to use CMOS transceivers that will record a logic
LO at a voltage level of 0 Volts.

The two transistor circuit may also be more susceptible to noise 
pickup.

Another point, the ALDL connector is shown on Sanjaya's
schematic, as well as Andrew Mattei circuit on Andy's site,
as a 10 pin connector. I'm not aware of any 10 pin connectors, 
(but I can be convinced otherwise) just the 12 pin ones
shown at Andrew's (official) home page:

   http://www.mindspring.com/~amattei/aldlif.jpg

I'd be interested in alternative views on this. I was unable
to find any kind of home page for Sanjaya Vatuk.

Peter
----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo@lists.diy-efi.org