From: jobarjo <jobarjo78_at_yahoo.fr>
Date: Thu, 18 Mar 2004 10:04:50 +0100

Fernando Birra wrote:

>Hi,
>
>"jobarjo" <jobarjo78_at_yahoo.fr> escreveu na mensagem
>news:004101c40c3f$47953410$520ca8c0_at_relax...
>
>
>
>>1k at 12v make 12mA, which may be too much for the archos.
>>Are you sure the archos fails to put the bus low with 5k at 12v? it makes
>>about 2mA, which should be largely possible.
>>This should be caused by your mosfet that cause a voltage drop...
>>
>>
>
>Yes, I'm quite sure. But I believe it is also caused by the transistor I'm
>using. The IBUS voltage drops just a little bit which probably means that
>the transistor is just barely starting to turn on. Is this a plausible
>explanation?
>
>
>
>
>>no need for a transceiver a simple npn, a resistor and your mosfet should
>>
>>
>be
>
>
>>ok
>>but need 2 wire...
>>
>>
>
>OK, I've done the serial mod already. I understand that I can use my mosfet
>to listen to the bus. But how do I connect the TX pin to the IBUS? Can you
>show it to me please?
>
>
>
very simple
your tx pin should be connected to a ~5k resistor which connects to the
base of the npn transistor (anyone but not a mosfet). the emiter
connected to the ground and the collector connected to the bus
This is called an open collector scheme.

don't forget that it inverts the data: a 1 on the tx pin will activate
the transistor and pull the bus to 0.

If you don't want to invert, you need a second pnp transistor and
another transistor.

I'm not sure, but there should be a possible solution to use your mosfet
as a transistor also... in this case you don't need any resistor.

>Thanks in advance,
>Fernando Birra
>
>
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>
>
>

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Received on 2004-03-18