Subject:
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Re: RCX sensor interfaces - diodes
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Newsgroups:
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lugnet.robotics.rcx
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Date:
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Fri, 28 Sep 2001 19:13:13 GMT
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Viewed:
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1893 times
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I think the real point here is that it is usually necessary
to incorporate a bridge network of six diodes to interface
to the RCX sensor inputs. The signalling current must pass through
at least two series diodes to get to the RCX terminals - a diode in
the ground side of the power bridge set of four and another in the
hot side of the signalling pair.
Using conventional junction diodes, you can expect to lose about
1.4 volts (as Stef points out, 2 x 0.7).
Since the RCX measurement range is 1.85 - 5.00 (100 - 0 light
sensor units) this only leaves 0.45 volts (1.85 - 1.4) of operating
headroom for the signalling element - commonly a constant current
transistor arrangement.
If you use schottky diodes instead, you'll increase the headroom by
about a volt which makes the design of the signalling element a lot
simpler!
JB
In lugnet.robotics.rcx, Stef Mientki writes:
> The main advantage of the BAT85 is the lower voltage drop (about 0.3 Volt
> against 0.7 Volt for the 1N4148).
>
> Chris Page wrote:
>
> > I'm in the middle or working out the circuit for my gray encoder sensor and
> > looking at the various interface schemes. I notice that most examples use
> > 1N4148 diodes, but one site I have visited (but I can't for the life of me
> > remember which :/) recommended BAT85 (Schottky barrier diodes) because they
> > "are more linear."
> >
> > Does anyone have any advice or opinion on this?
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