Go Back   VEX Forum > Official VEX Technical Support > UNOFFICIAL Answers - Ask the Community!

UNOFFICIAL Answers - Ask the Community! Community Members can provide UNOFFICIAL answers to the questions from the "locked" forum above.

Reply
 
Thread Tools
  #11  
Old 04-27-2012, 03:14 PM
jgraber jgraber is offline
Senior Member
 
Join Date: Nov 2006
Location: Dallas Texas metroplex
Posts: 1,109
Images: 13
Re: Legal use of Y-Cables?

Quote:
Originally Posted by Disciple855 View Post
Also, I wonder what would happen if the sensors being Y-cabled were different. Like say a Gyro and Potentiometer hooked up together.
Y of two potentiometers would likely provide an average of the two,
since there are no active circuits.
A Gyro has an active output buffer, so it would likely fight another active output.

Quote:
Originally Posted by magicode View Post
Y-cabling works for boolean sensors as an OR gate: the output is 1 if either inputs are 1, and 0 if both inputs are 0. I suppose you could use it to average analog sensors, but you would have to non linearly map the output (Ohms law). Using y cables to combine other digital sensors, or different sensors altogether will give you no meaningful data.
Almost right. Y cable on bumper switches will be an active-low logic wired-OR.
Default input value is 1, provided by an internal (to the Cortex) pullup resistor.
Pressing A OR B switch (which shorts signal line to Ground) will cause input to read 0 instead.
This type of wired-OR active low is common in electronic circuits.
For example, several daughter-cards on a mother-board can share an interrupt line with wired-OR, so any one of them can signal "hey, there is a problem".
The MB doesn't know who yanked its chain, so it has to go ask each board individually (polling).
Reply With Quote
  #12  
Old 04-27-2012, 03:35 PM
bobsalive bobsalive is offline
Senior Member
VEX # AURA
 
Join Date: Mar 2009
Location: Auckland, NZ
Posts: 321
Images: 4
Re: Legal use of Y-Cables?

Quote:
Originally Posted by jgraber View Post
Y of two potentiometers would likely provide an average of the two,
since there are no active circuits.
A Gyro has an active output buffer, so it would likely fight another active output.
Wouldn't a Y of two potentiometers basically put the two pots in parallel, causing you to receive a value that is related to (R1xR2)/(R1+R2) ? I guess it wouldn't be the same as (potValue1 x potValue2)/(potValue1 + potValue2) though, so might not be very useful anyway.
__________________
Andrew - andrew.chen@aura.org.nz
Reply With Quote
  #13  
Old 04-27-2012, 03:38 PM
Quazar's Avatar
Quazar Quazar is offline
Senior Member
 
Join Date: Aug 2007
Location: SF Bay Area
Posts: 1,231
Images: 16
Re: Legal use of Y-Cables?

Quote:
Originally Posted by bobsalive View Post
Wouldn't a Y of two potentiometers basically put the two pots in parallel, causing you to receive a value that is related to (R1xR2)/(R1+R2) ? I guess it wouldn't be the same as (potValue1 x potValue2)/(potValue1 + potValue2) though, so might not be very useful anyway.
You would have to be careful with putting two pots on a Y cable. If they are turned to opposite extremes you could have significant power flowing through them (in the neighborhood of 5W) which could damage them.

Cheers,
- Dean
Reply With Quote
  #14  
Old 04-27-2012, 03:46 PM
magicode's Avatar
magicode magicode is offline
Senior Member
VEX # 4542
 
Join Date: Sep 2010
Posts: 608
Images: 8
Re: Legal use of Y-Cables?

Quote:
Originally Posted by jgraber View Post
Almost right. Y cable on bumper switches will be an active-low logic wired-OR. Default input value is 1, provided by an internal (to the Cortex) pullup resistor. Pressing A OR B switch (which shorts signal line to Ground) will cause input to read 0 instead.
Yes, I am familiar with how the digital inputs work, I was referring to how they appear on a programming platform. ROBOTC at least registers 1 when the button is pressed and 0 when it isn't (if the senosr configured as a button, which the OP said he was using). I'm don't know if EasyC does this as well.
__________________
It's not a bug, it's a feature.
Reply With Quote
  #15  
Old 04-27-2012, 03:58 PM
jpearman's Avatar
jpearman jpearman is offline
Senior Member
VEX # 8888
 
Join Date: Apr 2011
Location: Los Angeles
Posts: 3,045
Images: 2
Re: Legal use of Y-Cables?

Quote:
Originally Posted by bobsalive View Post
Wouldn't a Y of two potentiometers basically put the two pots in parallel, causing you to receive a value that is related to (R1xR2)/(R1+R2) ? I guess it wouldn't be the same as (potValue1 x potValue2)/(potValue1 + potValue2) though, so might not be very useful anyway.
To make a log pot a fixed resistor is often put between the wiper and ground, this is the graph obtained using one pot midway and moving the other, a nice non linear curve.

Name:  pot2.jpg
Views: 228
Size:  32.2 KB

As quazar said, it's generally a bad idea as you can short power and ground with the pots at opposite ends. So the general rule here is don't do it.
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 04:41 AM.


VEX and VEX Robotics are trademarks or service marks of Innovation First International, Inc.
Copyright © 2002-2013. All Rights Reserved. VEX Robotics, Inc. is a subsidiary of Innovation First International, Inc.
All other product names/marks of others are the property of their respective owners.