Can I use reed switch as RCX sensor without resistor?

[mikezang]

I want to use reed switch as RCX sensor, RCX will get signal when trains with magnate pass on it.

I want to know if I can connect reed switch to RCX input port without any resistor? Do I have to use a resistor with reed switch?

[Chas]

Don't own an RCX but the schematic for the NXTT specifies a 2.2k resistor between the switch and the output connector (current limiter). This site has alot of excellent rcx stuff on it so try here and see if you can find some info:

http://www.philohome.com/nxt.htm

I would say use the resistor as it will not interfere with the signal path and better safe than sorry!

[kieran]

I think the resistor is to make sure that the sensor port is tied low or high before closing the read switch, if this is not there the value being sensed may not be a zero or 1

[mikezang]

I just found this picture from article http://www.convict.lu/Jeunes/ultimate_stuff/Making%20your%20own%20RCX%20sensors_part2.pdf,

It seems like it should be ok even if no resistor? Is it right?

Edited April 16, 2014 by mikezang

[Chas]

pull up sounds more thesable. Again, don't know the config of the RCX but the one in the nxt is a pull up when i checked the brick schema

[mikezang]

I also found these pictures here http://www.brickshelf.com/cgi-bin/gallery.cgi?f=16667, then reed switch has hundreds ohm when it is on.

[Philo]

Because of its construction (conductive rubber) RCX sensor bas an internal series resistor of about 500 ohm. This acts also to limit current if switch is inadvertently connected on a motor port. For the same reason NXT sensor has a 2.2k series resistor. Except for this protection function it is not useful, so I wouldn't bother to add it.

[Zerobricks]

Maybe you could use it for swiitch to LED's...

[Boxerlego]

What is it you are trying to control with the reed switch?

[mikezang]

What is it you are trying to control with the reed switch?

Train auto control system.

[Snapshot]

I've controlled trains using reed switches without resistors with NXT and the results are in the video here. I extended it to control multiple trains but found that as the IR signals are so slow to send it was only possible to have one train moving at a time.

[mikezang]

I've controlled trains using reed switches without resistors with NXT and the results are in the video here. I extended it to control multiple trains but found that as the IR signals are so slow to send it was only possible to have one train moving at a time.

Can you show me your reed sensor built and how to use them? Where is your NXT at? What do you mean only one train moving at a time? Can you explain more detail?