How To Add Led Indicator And Avoid Voltage Drop - Arduino Forum

How to add led indicator and avoid voltage drop Other Hardware General Electronics system May 11, 2014, 8:29pm 1

I believe my question would be stupid to those who understand electronics better then me, but really I couldn't find answer myself.

I successfully use L293D Motor Driver Dual H-Bridge Motor Driver for DC or Steppers - 600mA - L293D : ID 807 : $8.95 : Adafruit Industries, Unique & fun DIY electronics and kits to control DC motors as demonstrated on this schema: and I want to add LED indicators connected to INPUT pin and GND, surely I connect LED with a series resistor which leads to voltage drop so basically arduino sends to driver 3 volts instead of 5.

So my question how I can safely add LED indicator to see which input is triggered but avoid voltage drop.

Thank you.

system May 11, 2014, 8:41pm 2

Your input pin will still see 5v as the potential difference between the pin and the input pin is 5v irrespective of what goes on in between the arduino and the input pin.

MarkT May 11, 2014, 8:46pm 3

Without the series resistor you would overload the pin and pull it well below 5V. The series resistor takes up the difference between led voltage and 5V and so long as you don't pull too much current from the pin it will be fine.

Your circuit shows the motor power going through the voltage regulator - that's not a good idea - have the motor supply direct from the battery.

system May 11, 2014, 8:50pm 4

calvingloster: Your input pin will still see 5v as the potential difference between the pin and the input pin is 5v irrespective of what goes on in between the arduino and the input pin.

So you say that even if I put a led with resistor the pin on l293d driver will see incoming voltage as 5 volts? But when I test it with multimeter it shows me that voltages is ~3.2V

system May 11, 2014, 9:06pm 5

MarkT: Without the series resistor you would overload the pin and pull it well below 5V. The series resistor takes up the difference between led voltage and 5V and so long as you don't pull too much current from the pin it will be fine.

Your circuit shows the motor power going through the voltage regulator - that's not a good idea - have the motor supply direct from the battery.

yeh, but how can I achieve my goal, maybe there is some other way to connect led indicator so original destination still receives 5V and LED is regulated with a resistor?

Zapro May 11, 2014, 11:33pm 6

Look at this pic. You can place the LED in two ways. One way, it lights up when the output of the Arduino is "High" and the other, it will light when it is "Low"

// Per.

Screen Shot 2014-05-12 at 01.35.04.png857×1139 7.61 KB

system May 12, 2014, 9:25am 7

Zapro: Look at this pic. You can place the LED in two ways. One way, it lights up when the output of the Arduino is "High" and the other, it will light when it is "Low"

// Per.

I want to trigger LED when voltage is HIGH and this is exactly what I already tried, but connecting LED with series resistor like this reduces input voltage to driver input pin from 5V to 3V because of the series resistor, so I feel that this is not the best way to approach.

Or you trying to say that it doesn't matter that I have voltage drop? Sorry I still confused about this...

Zapro May 12, 2014, 9:39am 8

endryha: I want to trigger LED when voltage is HIGH and this is exactly what I already tried, but connecting LED with series resistor like this reduces input voltage to driver input pin from 5V to 3V because of the series resistor, so I feel that this is not the best way to approach.

Or you trying to say that it doesn't matter that I have voltage drop? Sorry I still confused about this...

If your output signal drop to 3 volts, there are 2 possibilities. Either you are using too low a resistance or no at all, and the LED "shunts" the voltage heavily, which will eventually break your Arduino. Otherwise, you have the resistor placed incorrectly. Look at my drawing attached.

// Per.

Screen Shot 2014-05-12 at 11.38.50.png1312×1147 14.7 KB

MarkT May 12, 2014, 9:55am 9

The resistor should be 150 ohms or greater. Even if the voltage drops a little to say 4V the L293 will still be happy.

If the L293 is damaged it could be pulling its input pin low, but that's easy to check since the presence of the LED wouldn't affect this.

system May 12, 2014, 10:35am 10

Ok, thank you all for explanations I will verify one more time and let you know.

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