Sorry to bother you guys but I’m in the process of developing a little project with my Panda Fez II. I’m also trying my hand at drawing a correct electronic diagram for it also, could someone tell me if the circuit looks okay and I’m using the correct symbols? Any feedback is welcome, or pointers about better ways of documenting my project.
The MOSFET I’ve used here is http://uk.farnell.com/jsp/search/productdetail.jsp?sku=1708441.
Looks ok to me. One thing just to make sure Pic GND and GND should be connected together.
I’m reading through the datasheet, trying to figure out why it’s so different than any other MOSFET datasheet I’ve ever seen, and then I realize, it’s a MOSFET-output “solid state relay”, or what I will now refer to as an “opto-MOSFET”, as opposed to an “opto-triac”, which is the same thing, except for AC instead of DC. Very nice.
Your diagram (schematic) isn’t accurate, however, because it shows the connection of an actual MOSFET. What this device is, essentially, according to the Panda II, is simply an LED. You “drive” it just like you’d drive an LED. Pay attention to the forward voltage and forward current numbers from the datasheet.
To drive this from 3.3V, assuming the datasheet’s 1.3V typical forward voltage is correct, a 470 ohm resistor would give you 4.3 mA of LED current. The datasheet recommends between 5 and 20, so that’s a little on the low side. Your 100 ohm resistor would give you 20 mA, which is the limit at the high end. I’d probably shoot for closer to 10 mA, just because I like to play it safe. That means somewhere in the 220 ohm range.
Oh, and finally, since this is opto-isolated, you don’t need to worry about connecting the MOSFET’s ground to the Panda II’s ground.
Fantastic replies. Thank you both.
Just looked at the datasheet. I agree with godefroi. Also change schematic symbol from MOSFET to the one used in the datasheet to avoid any confusion and properly indicate opto isolation.