Voltage Drop?

James Newman

Ok, in my current project I'm going to need to check a couple of buttons and a switch, each being a few feet from the propeller itself. If this where an output type thing I would place some mosfets or optoisolators in there and use a 24V separate circuit for the long wires... however since it's input, I'm a little stumped. Will running from 3.3 or maybe the 5 volt lines from the propeller work with such long wires? (Sorry, don't have them here, so not sure on their gauge.) If not, any suggestions? Maybe some 24V activated relays? None of my current relays or transistors can handle 24V...

deSilva

"A few feet" can be an understatement: 100? 1000? What problems do you expect? Much depends on the actual environment. You say "switch"... they do not work them with 10 kHz, do they?

(1) Any twisted wire would do for 100 m, I should say... If you have high RF or strong motors around you can take shielded wires.

(2) Worst case you can take three wires (+, GND, data-in), connecting data-in to GND by a 1k resistor close to the switch (you need a pull-down anyway); the switch will go to +, I presume..

(3) You could also protect the Propeller input by a 10 k resistor against possibly induced higher voltage; however this will not be the case when you use solution (2).

James Newman

It will be around 6 foot to the buttons, only 3 to the switch. Not sure on the ratings for the switch, I may replace it with a more suitable one. All of these are polled, and should remain 'active' for atleast half a second. I havn't looked at the cables to see if they are twisted, but they are shielded.

deSilva

So there is no problem at all with Ohm
What I do not like is a long open wire....

I should suggest (B) rather than (A):

(A)
Pop-Up (10k)              !!
Vdd -/\/\-+             ------  
          |             o    o
          |             |    |
Prop O----+-...---------+    |
                             |
 Vss -------...--------------+


(B)
Pop-Up (1k)               !!
Vdd -/\/\-+             ------  
          |             o    o
          |             |    |
Prop O----+-...---------+/\/\+ 2k2
                             |
 Vss -------...--------------+

In fact this is 1mA current loop and will work for quite long lines..
But I am not an export for long wires.

James Newman

deSilva> Ok, so if I understand that right... when the switch is closed, the prop will sense high from the pull up, then when the switch is opened it will pull the line down, and the prop will sense low. Finally, the 2k2 resistor provides a way for any stored charge in the line, due to capacitance, to dissipate?

Lol, I'm such a newbie to electronics... programming is simple, but I've just started playing with electronics in the last couple months. Thanks for the help.