From: Fernando Birra <fpb_at_di.fct.unl.pt>
Date: Fri, 12 Mar 2004 08:31:36 -0000

Hi,

I tried to interface the archos to the BMW IBUS (serial line pulled up to
12V and brounght down to 0 by the talker) but only partailly managed to do
it. I have an RS232 adaptor to talk to the bus with a PC and I used it to
debug the trasmit routines. So, I can send and receive packets to the bus
with the archos with this setup:

PC <-> RS232-IBUS adaptor <-> IBUS wire <-> MOSFET Level Shifter (3V-12V)
<-> Archos

The connections on the MOSFET are:

Source - Archos Remote Control Pin
Gate - 3V Power Suppy
Drain - BMW IBUS

However, when I plug the archos with the mosfet level shifter to the car bus
I can receive (sometimes with errors) but I cannot send. I managed to
identify the problem but I don't know the solution...

The trouble is that when I connect the archos to the car bus with the mosfet
level shifter (I used a BS170) when the archos forces the bus low it can
only bring it to around 1.2 Volts and when I look to the drain pin I still
see around 12V. If I short circuit the ground with the source pin then I can
bring the drain pin (connected to the car BUS) to around 0V.

I really don't know how to solve this and it would be great if you could
help me. Would it help connecting to a different MOSFET with a lower Vgs
threshold value?


Thanks
Fernando Birra


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Received on 2004-03-12