# how to put led to indicate the signal is functioning

I want to connect an input signal to pc817 and the output to a microcontroller. I don't know how to put the LED at the input to indicate that the input signal is working.

For example my input is limit switch. My $V_{in}$ is 3.3V. Before the limit switch is closed, the voltage at the first pin of optocoupler should be the forward voltage 1.4V. After the limit switch is closed, the voltage become 3.3V. So my question here is how to connect the LED to the input and how to connect the signal of the input to the optocoupler. other than limit switch i will use digital or analog sensor as input to be isolated and interface to the microcontroller. i would like to make the led as the indicator when the sensor is sensing object, and the led will light. so how to make the led work like that.

• Connect the indicator LED in parallel with the optocoupler's LED. And don't forget to put current-limiting resistor in series with each of the LEDs. – m.Alin Mar 21 '13 at 7:33
• Please add a schematic or at least a hand-drawn sketch of what you have done so far, and what you are trying to achieve. An image is easier to grasp at a glance, than a verbal description. As you do not yet have sufficient reputation for posting images, upload to any public image hosting site and post the link as a comment here. Someone will edit your images into the question. – Anindo Ghosh Mar 21 '13 at 7:34
• Huh? You want to connect a input signal to a "PIC817". There is no such PIC, perhaps 16F817? Then you want the output (whatever that is) to go to a microcontroller. But the PIC already is the microcontroller. Then the schematic you show has no microcontroller in it at all. It is impossible to tell what is being asked here. – Olin Lathrop Mar 21 '13 at 12:15