
ELM334
< http://www.elmelectronics.com/ >Connection Diagram
PDIP and SOIC
(top view)
V
DD
V
SS
1
2
3
4
8
7
6
5
Garage Doorman
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.
ClosedSw
RLED
GLED
Description
Garage door monitoring and control
Remote signalling and acknowledgement
Applications
Block Diagram
1 of 4
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
Features
ELM334DSB
OpenSw
Control
PB
5
Control
Debounce
Timers
4
PB
ClosedSw
GLED
7
OpenSw
2
RLED
6
3
Output
Limitter
Debounce
Timers
Debounce
Timers
Drive
Logic