ELM334
Garage Doorman
Description
The ELM334 is a handy circuit for remotely
monitoring the position of your garage door. A two-
wire interface is all that is needed to convey the
position of the door to two remotely located LEDs,
and to also provide control for an electric opener if
desired.
This circuit continually monitors the state of two
position sensing switches, representing the fully
open and fully closed positions of the door. After
suitable debouncing, the states of these switches
are used to vary the polarity of the two signal wires,
resulting in either the red (open) or green (closed)
LED turning on. When the door is in neither position
(moving), the LEDs rapidly alternate between the
two colours.
If desired, circuitry to detect a short between the
two LED wires can be added and used to operate a
control output. If the door is equipped with a
standard electric opener, this control signal can be
used to operate the door. Refer to the Example
Application section for further details.
Features
• Low power CMOS design
• Wide supply range - 3.0 to 5.5 volt operation
• Simultaneous monitoring of three inputs
• Fully debounced inputs
• Two wire interface
• Stuck button protection on the control output
• Control function is an optional addition
Connection Diagram
PDIP and SOIC
(top view)
V
DD
RLED
GLED
1
2
3
4
8
7
6
5
V
SS
OpenSw
ClosedSw
Control
Applications
• Garage door monitoring and control
• Remote signalling and acknowledgement
PB
Block Diagram
RLED
2
Debounce
Timers
Drive
Logic
7
OpenSw
GLED
3
Debounce
Timers
6
ClosedSw
PB
4
Debounce
Timers
Output
Limitter
5
Control
ELM334DSB
Elm Electronics – Circuits for the Hobbyist
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