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No, the RCX knows nothing about the diodes. That is why devices like the
light sensor only send a current signal in the range 0 - 0.32mA back to the
RCX. This current then creates a voltage drop across the 10k reference
resistor with respect to the 5v supply.
By using a current signal rather than a voltage one, the unknown drop across
the diodes doesn't matter as long as it doesn't exceed a certain minimum.
All the more accurate sensors mostly use this technique.
JB
In lugnet.robotics.rcx.legos, Samuel Winchenbach writes:
> Hello all,
>
> I recently purchased "Extreme Mindstorms - An Advanced Guide to LEGO
> Mindstorms" and I must say it is one of the best books out there for the
> power user.
>
> I have a number of questions regarding powered sensors. First of all, when
> the RCX goes to make a the reading on a powered sensor it drops the output
> voltage from 7 to 5 volts, and then takes a reading. Does the RCX take
> into account the two diode drops (D5 or DG and D1 or D2) I would assume
> that it must, otherwise when the leads are shorted it would still be reading
> 1.4 volts... which is not correct. So I would assume that there is some
> form of offset in the RCX or something?
>
> also, in figures 10-5, and10-7 (in all the powered sensors for that matter)
> what is 1K resistor used for? it appears to be some form of current
> limiting resistor, but from understanding of the internals of the RCX, there
> is a 10K resistor in series with it.
>
> If anyone can help answer these questions it would be greatly appreciated,
> thanks.
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Message has 2 Replies:
 | | Re: Powered Sensors
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| ----- Original Message ----- From: "John Barnes" <barnes@sensors.com> Newsgroups: lugnet.robotics.rcx.legos Sent: Tuesday, May 07, 2002 2:23 PM Subject: Re: Powered Sensors (...) the (...) across (...) Ok... lets see if I understand this.... For (...) (23 years ago, 7-May-02, to lugnet.robotics.rcx.legos)
| | | Re: Powered Sensors
|
| Ok, I have gotten myself confused again. 0-0.32mA represents a voltage dropbetween 0 - 3.2 volts. Therefore the voltage that the RCX "reads" on theA2D is between 5 - 1.8 volts (1023 - 368 RAW)? To get a reading of 0 (RAW)it seems as though you would (...) (23 years ago, 8-May-02, to lugnet.robotics.rcx.legos)
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Message is in Reply To:
| | Powered Sensors
|
| Hello all, I recently purchased "Extreme Mindstorms - An Advanced Guide to LEGO Mindstorms" and I must say it is one of the best books out there for the power user. I have a number of questions regarding powered sensors. First of all, when the RCX (...) (23 years ago, 7-May-02, to lugnet.robotics.rcx.legos)
|
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