Thanks, for your quick answer. I have just realised that I power the Seed by USB, so no VIN and therefor no +5V available.Can I power the 6n138 in 3.3V ? Does the R value will change ?
Thanks by advance
The Daisy Seed also operates on 3.3vdc, so, yes you can replace the Teensy with a Daisy Seed without modifying your circuit. I should have said that the Daisy reduces the USB 5vdc to 3.3vdc and uses that for it’s IO. But still, yes, it will work no problems as there is no need to step down the voltage.