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ELM334 Garage Doorman
Description
The ELM334 is a handy circuit for remotely monitoring the position of your garage door. A twowire 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) www.DataSheet4U.com 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)
VDD RLED GLED
1 2 3 4
8 7 6 5
VSS 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 < http://www.elmelectronics.com/ >
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ELM334
Pin Descriptions
VDD (pin 1) This pin is the positive supply pin, and should always be the most positive point in the circuit. Internal circuitry connected to this pin is used to provide power on reset of the microprocessor, so an external reset signal is not required. Refer to the Electrical Characteristics section for further information. RLED (pin 2), and GLED (pin 3) These two pins are for driving a red and a green LED through a current limiting resistance. Typically the LED used will be a dual type, that www.DataSheet4U.com appears white if not energized, red if energized in one polarity, and green if the polarity is reversed. Alternatively, two discrete LEDs could be wired ‘back-to-back’. During powerup, the red LED will be lit for 0.5sec, followed by the green for 0.5sec, and then the circuit will alternate between the two for a further 0.5sec. PB (pin 4) A momentary low level signal on this pin will cause the control output to go high, after approximately 25msec delay due to the internal debounce circuitry. If unused, this pin should be connected to VDD. Control (pin 5) This output goes to an active high level (VDD), in response to a valid low level on pin 4. The duration of the output will be the same as the input, to a.