hi everyone!
well, i thought i had it figured out but things aren't working as they should; let me explain. i've bought an optocoupler (the LTV-826 http://www.mouser.com/ds/2/239/LTV-8x6-201828.pdf) which I'm using to trigger my camera by means of an Arduino Due (logic at 3.3V). I understand that I need a current limiting resistor on the input side of the optocoupler, so here is how I calculated it:
From the datasheet, we see that the forward voltage is (typically, @20mA) 1.2V; so subtracting 1.2V from 3.3V leaves us with 2.1V for us to deal with through the resistor. So, by Ohms law 2.1V / .02A = 105 Ohms. So, I put in a 100 Ohm resistor.
Here is how I've got things hooked up:
- straight off the digital pin (of the Arduino Due) I've got the resistor
- from the resistor I go to the anode of the optocoupler input (pin1 in the datasheet)
- i've got the cathode going to GND (pin2 on the datasheet)
(not that I write that, I wonder if it matter that the resistor is on the anode side and not the cathode??)
When I throw the pin connected to the input side of the optocoupler high (3.3V) and I check the resistance on the output side of the optocoupler, I'm not getting 0 resistance like I'm expecting.
I'm guessing I'm not using the proper value for the current limiting resistor; so I'm hoping someone could show me how to calculate for the proper one?
Thanks a million everyone!
well, i thought i had it figured out but things aren't working as they should; let me explain. i've bought an optocoupler (the LTV-826 http://www.mouser.com/ds/2/239/LTV-8x6-201828.pdf) which I'm using to trigger my camera by means of an Arduino Due (logic at 3.3V). I understand that I need a current limiting resistor on the input side of the optocoupler, so here is how I calculated it:
From the datasheet, we see that the forward voltage is (typically, @20mA) 1.2V; so subtracting 1.2V from 3.3V leaves us with 2.1V for us to deal with through the resistor. So, by Ohms law 2.1V / .02A = 105 Ohms. So, I put in a 100 Ohm resistor.
Here is how I've got things hooked up:
- straight off the digital pin (of the Arduino Due) I've got the resistor
- from the resistor I go to the anode of the optocoupler input (pin1 in the datasheet)
- i've got the cathode going to GND (pin2 on the datasheet)
(not that I write that, I wonder if it matter that the resistor is on the anode side and not the cathode??)
When I throw the pin connected to the input side of the optocoupler high (3.3V) and I check the resistance on the output side of the optocoupler, I'm not getting 0 resistance like I'm expecting.
I'm guessing I'm not using the proper value for the current limiting resistor; so I'm hoping someone could show me how to calculate for the proper one?
Thanks a million everyone!