Parallax Reed Switch User manual

Web Site: www.parallax.com
Forums: forums.parallax.com
Sales: [e-mail]
Technical: [e-mail]
Office: [phone]
Fax: [phone]
Sales: [phone]
Tech Support: [phone]
© Parallax, Inc. • Reed Switch (#910-27225) • v1.0 5/07 Page 1 of 3
Reed Switch (#910-27225)
General Description
A Reed Switch is similar to a standard switch in that it makes/breaks an electrical connection. Unlike a
push button switch though, a reed switch works via magnetic field. This reed switch is normally open
(N.O.), which means when no magnetic field is present the contacts/circuit are open.
Features
Sealed Design
Normally Open Contacts (SPST)
Includes Magnet
Application Ideas
Alarm Systems
Robotics
Industrial Control
Quick Start Circuit
Connecting and Testing
The above diagram is equivalent to the Active-Low switch circuit shown in our BASIC Stamp Reference
Manual as well as the BASIC Stamp Editor Help File. When the magnet is in proximity to the reed switch
the contacts will be closed. This circuit is very common in alarm systems because it offers the best
immunity to noise and EMI/RFI interference. The magnet would be mounted inside the door or window
edge and the reed switch would be connected to the frame. If the door or window was opened the
magnetic field would move away opening the contacts and allowing the I/O pin to go high.

© Parallax, Inc. • Reed Switch (#910-27225) • v1.0 5/07 Page 2 of 3
Calibration
Since the reed switch works on magnetic fields it is important to make sure the magnet you use is setup
to properly affect the reed switch and give consistent switching. Magnets are polarized devices so
orientation will affect performance. Please follow the guidelines below to help adjust your setup.
√Mount the reed switch in the location best suited. The magnet is usually easier to reposition.
√Determine the optimum distance/orientation of the magnet which opens/closes the reed switch.
Remember, different magnets will give different performance depending on size/type. You can either
glue the magnet to the surface or drill a hole and embed it into the edge of a door/window.
Specifications
Electrical Characteristics
Maximum Switching Power 15W
Maximum Switching Current 1A
Maximum Carrying Current 2.5A
Maximum Switching Voltage 200VDC
Breakdown Voltage 300VDC
Initial Contact Resistance .1Ω
Module Dimensions

© Parallax, Inc. • Reed Switch (#910-27225) • v1.0 5/07 Page 3 of 3
BASIC Stamp®2 Program
This program displays the current status (open/closed) of the Reed Switch in the DEBUG window. This
could be used to calibration of the switch/magnet or for testing/debugging purposes.
' =========================================================================
'
' File...... ReedSwitchTest.bs2
' Purpose... Display Status Of Reed Switch
' Author.... Parallax, Inc.
' E-mail.... [email protected]
' Started... 05-15-2007
' Updated...
'
' {$STAMP BS2}
' {$PBASIC 2.5}
'
' =========================================================================
' -----[ I/O Definitions ]-------------------------------------------------
ReedSwitch PIN 0 ' Reed Switch Input Pin
' -----[ Program Code ]----------------------------------------------------
Main:
DO
IF IN0 = 0 THEN ' Is Reed Switch Closed?
DEBUG HOME, "CLOSED", CLREOL ' CLOSED. Display It
ELSE
DEBUG HOME, "OPEN", CLREOL ' OPEN. Display It
ENDIF
PAUSE 150 ' Wait A While
LOOP ' Keep Going