hi i am playing around with optocoupler to supply input signal to uno.
i am using the blink sketch to output and digiralRead on same board to detect input.
if i Serial.print after digitalRead the digitalRead does not work i.e. input is hi always.
if i put a Serial.print brfore digitalRead the input changes.
i have a copy of sketch and wiring, can someone advice me how to up load documents
yes that's needed (optocouplers require a current limiting resistor, do you have one?)
Read this: 'How to get the best out of this forum' - it's all in there...
Upload, by simply dragging the image file, into the reply window.
For uploading code see How to get the best out of this forum
yes i have a resistor. i also have a led connected to output of optocupler to show device is working. my problem is the sketch and the location of "Serial.println(" low ");"
if i put this line before "Serial.println(digitalRead(ledin));" the print is correct.
if i put "Serial.println(" low ");" after, the print is 1 always
post everything so we can have a look
unable to load attachment as i am classed as a new uder
ah keep posting a bit and you'll be granted the rights 
you should already be able to copy and paste the code here (make sure you use code tags and indent the code before posting here)
this is the code that i am using. take note where *************
int ledin = 2;
void setup() {
// initialize digital pin LED_BUILTIN as an output.
pinMode(LED_BUILTIN, OUTPUT);
pinMode(ledin, INPUT);
Serial.begin(9600);
Serial.print(" photo optic test ");
}
// the loop function runs over and over again forever
void loop() {
digitalWrite(LED_BUILTIN, HIGH); // turn the LED on (HIGH is the voltage level)
//Serial.println(" high ");
Serial.println(digitalRead(ledin));
Serial.println(" high ");
delay(1000); // wait for a second
digitalWrite(LED_BUILTIN, LOW); // turn the LED off by making the voltage LOW
Serial.println(" low "); // turn print on digitalRead work*************
Serial.println(digitalRead(ledin));
//Serial.println(" low ");
delay(1000); // wait for a second
}
I edited your post and added the code tags and the indentation...
Please do yourself a favour and please read How to get the best out of this forum and post accordingly in the future.
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can you describe with words what the circuit / power looks like?
output from uno pin 13 though 22o ohm to pin 1 optocoupler and pin 2 to earth.
5v to pin 5 optocoupler and pin 6 though 10k to earth. pin 6 optocoupler to uno pin 2.
also pin 6 optocoupler though 220 ohms and led to GND. led is on when pin 13 led is on, this tells me the optocoupler is working. sketch will work if i put a print in a spot and does not work if i remove the print
what's the reference of your optocoupler?
looks like this ?
that looks correct. 4N25 is number
Your code is missing
pinMode(13, OUTPUT);
in the setup function.
code is a modified version of blink code from example file.
pinMode(LED_BUILTIN, OUTPUT); i am on the understanding that this is pin 13 by default.
if the led and resistor is connected to pin 13, led will turn on and off at a control rate.
if i try to define this, code will error
That depends on the processor.
What Arduino are you using?
i am using UNO
Which UNO - the R4 is very different from R3 and earlier ...
i am using arduino UNO R3.
if i wire to match your diagram, i get no input at all.
the way i had it i could get an input.
my question is why does the Serial.println(" low "); line effect the Serial.println(digitalRead(ledin)); line. if print is before read, code works and if print is after read, code does not work.