> I've talked about this before, and this is probably the weirdest
> part of the new furnace controller, so I'm open for input.
Second try. Still no optos, but used the 2.5V idea to bias the first
stage MOSFETS, so that a "floating" output makes Vgs zero for both
MOSFETS, and an active signal dr
> Is using the two pins to create an I2C port an option?
Well, I need to signal fast enough (and with sufficiently reliable
timing) to drive the 1wire bus. Besides, it's not a lack of pins
that's the problem (I can switch to the 144 pin version and gain 44
GPIO pins), it's the flexibility and EM
On 5/12/06, DJ Delorie <[EMAIL PROTECTED]> wrote:
> Have you looked at the parts from Allegro?
Not until just now, but I don't see anything that would fit. Which
ones were you thinking of?
When I quickly read the email I saw "two wires" and "high current IO"
and thought
MAXIM port expander
> The gate drive BJT's, being single ended, can't pull the gates to
> "off" actively.
Oops, forgot the pull-down resistors. Imagine a pair of pull-down
resistors from the MOSFET gates to the other supply ;-)
The reason for the emitter followers is to properly bias the MOSFET
gates when the GPIO
> Have you looked at the parts from Allegro?
Not until just now, but I don't see anything that would fit. Which
ones were you thinking of?
Just scratching the surface here, but, there doesn't appear to be a bias path
for your BJT's in this ckt. The mosfets depend on leakage (in the bjt and in
their gates) to turn off. The gate drive BJT's, being single ended, can't
pull the gates to "off" actively. The circuit depends on leakage t
On 5/12/06, DJ Delorie <[EMAIL PROTECTED]> wrote:
The goal is to, essentially, create a high current filtered tri-state
I/O port, using two GPIO pins. Details on the web page:
http://www.delorie.com/house/furnace/pcb2/io_port.html
Have you looked at the parts from Allegro?
http://www.allegro
I've talked about this before, and this is probably the weirdest part
of the new furnace controller, so I'm open for input.
The furnace controller will have eight of these I/O drivers, two per
zone. Nominally one for input and one for output, but in my case it's
one for the dallas 1wire interfac
