Garage door opener puzzle
Trying to find out why operation is erratic, I measured the voltage
across the hard-wired pushbutton in the garage. The button is illuminated by a red LED, which is in series with a 1k resistor across the switch. The LED is always on. Pressing the switch shorts the resistor-LED pair and operates the door. The puzzle is that when I disconnect the LED-switch assembly and measure the voltage across the wires from the opener unit, I get only a couple hundred millivolts DC, and less AC. How is it possible for the LED to light with only 200 mV across it? Isaac |
Garage door opener puzzle
isw wrote:
Trying to find out why operation is erratic, I measured the voltage across the hard-wired pushbutton in the garage. The button is illuminated by a red LED, which is in series with a 1k resistor across the switch. The LED is always on. Pressing the switch shorts the resistor-LED pair and operates the door. The puzzle is that when I disconnect the LED-switch assembly and measure the voltage across the wires from the opener unit, I get only a couple hundred millivolts DC, and less AC. How is it possible for the LED to light with only 200 mV across it? it's a pulsed waveform that you can't measure with a regular DVM maybe? |
Garage door opener puzzle
In article , frank
wrote: isw wrote: Trying to find out why operation is erratic, I measured the voltage across the hard-wired pushbutton in the garage. The button is illuminated by a red LED, which is in series with a 1k resistor across the switch. The LED is always on. Pressing the switch shorts the resistor-LED pair and operates the door. The puzzle is that when I disconnect the LED-switch assembly and measure the voltage across the wires from the opener unit, I get only a couple hundred millivolts DC, and less AC. How is it possible for the LED to light with only 200 mV across it? it's a pulsed waveform that you can't measure with a regular DVM maybe? Hmm. Could be. Time to limber up the ol' wiggle tube. Isaac |
Garage door opener puzzle
On Tuesday, August 2, 2016 at 1:52:56 PM UTC-4, isw wrote:
Trying to find out why operation is erratic, I measured the voltage across the hard-wired pushbutton in the garage. The button is illuminated by a red LED, which is in series with a 1k resistor across the switch. The LED is always on. Pressing the switch shorts the resistor-LED pair and operates the door. The puzzle is that when I disconnect the LED-switch assembly and measure the voltage across the wires from the opener unit, I get only a couple hundred millivolts DC, and less AC. How is it possible for the LED to light with only 200 mV across it? Isaac Reconnect the LED/resistor and remeasure. |
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