Withdrawn         LSA    Limit Switch Adapter                       

Listed here for reference only .

Use Lego switch sensors as limit switches, without an RCX sensor input!

The Limit Switch Adapter is for use with the Lego Mindstorms™  Robotic Invention System.
It lets you use a standard Lego sensor switch as a limit switch.  A limit switch will automatically stop a motor when it reaches the desired position.  The Limit Switch Adapter will allow you to do this without using an RCX sensor input.  This is a good way to learn about limit switches.
 

     Limit Switch Adapter    .
 

In the picture below, a single switch is used to stop the crossing gate in it's raised position.

       LSA Connection.
 

Specifications

• Size: 2 bumps by 8 bumps.  Height is one and one third brick.  (brick plus flat plate).
• Lego electric plate connector on bottom.
• Two switch inputs to stop at both ends of travel.
• Works with any polarity.
• Works with all Lego motors.
• Works at all Mindstorms motor power levels.
• Motor braking when the motor is turned off.
• Arc surpressor protects relay contacts.

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Technical Description

The Lego switches send current through a diode to an opto-isolator.  The opto-isolator controls current to a relay.  The relay controls power to the motor.  A capacitor stores power so the relay does not chatter when Mindstorms is set for low power output.  A second set of contacts on the relay is used to short the motor terminals when the motor is turned off.  This provides a braking function, so movement stops immediately.  Back-to-back zener diodes prevent arcing when the relay opens, extending the relay contact life.  The entire circuit is designed to minimize power drain when the motor is switched off.