ghostintranslation
Well-known member
Hi,
In order to protect the serial Rx pin 0 on Teensy 4.0, I've made a pcb with a 6n137s like that:

But it's not working.
My goal is to be able to connect another teensy serial Tx but also any midi din cable that's why i need the optocoupler.
At the moment I'm trying with another Teensy to this Teensy.
I tried removing D1 which is there to protect from reverse voltages but even without it doesn't work.
I think this is coming from R7 that drops the current too much but Im not sure... since it's done on a pcb with super tiny format (I did it with JLCPCB) I can't easily remove and replace the resistor, but even if I shortcut that resistor it doesn't work actually...
And I can pinpoint the issue being on the optcoupler because if I take the incoming serial and wire it to the out of the optocoupler (pin 6) it makes it to Teensy and it's readable.
I tried also wiring a LED just to see if it lits to try to debug this. If I connect the led between the 2 pins of the incoming jack connector, it lits. If I connect between the jack connector and the left side of the resistor it lits. Now if I connect it between the jack connector and the right side of the resistor it doesn't. Which makes me think it's because the current is to low then?
Then I measured with a multimeter. I get 1.8V and 15ma between pin 2 and 3 of the optocoupler, and if I refer to the datasheet, https://media.digikey.com/pdf/Data Sheets/Lite-On PDFs/6N137 Series.pdf , I need 1.45V / 1.7V and 25ma, so that tends to confirm my issue?
So then why doesn't it work when I shortcut R7?
Is it possible to get the Serial of a Teensy through an optocoupler at all? Will I be able to make the otpocoupler work for both the Serial of a Teensy and a MIDI DIN connector?
I'm not an expert in electronics, I'm better at code, so I'd appreciate any help.
Thank you
In order to protect the serial Rx pin 0 on Teensy 4.0, I've made a pcb with a 6n137s like that:

But it's not working.
My goal is to be able to connect another teensy serial Tx but also any midi din cable that's why i need the optocoupler.
At the moment I'm trying with another Teensy to this Teensy.
I tried removing D1 which is there to protect from reverse voltages but even without it doesn't work.
I think this is coming from R7 that drops the current too much but Im not sure... since it's done on a pcb with super tiny format (I did it with JLCPCB) I can't easily remove and replace the resistor, but even if I shortcut that resistor it doesn't work actually...
And I can pinpoint the issue being on the optcoupler because if I take the incoming serial and wire it to the out of the optocoupler (pin 6) it makes it to Teensy and it's readable.
I tried also wiring a LED just to see if it lits to try to debug this. If I connect the led between the 2 pins of the incoming jack connector, it lits. If I connect between the jack connector and the left side of the resistor it lits. Now if I connect it between the jack connector and the right side of the resistor it doesn't. Which makes me think it's because the current is to low then?
Then I measured with a multimeter. I get 1.8V and 15ma between pin 2 and 3 of the optocoupler, and if I refer to the datasheet, https://media.digikey.com/pdf/Data Sheets/Lite-On PDFs/6N137 Series.pdf , I need 1.45V / 1.7V and 25ma, so that tends to confirm my issue?
So then why doesn't it work when I shortcut R7?
Is it possible to get the Serial of a Teensy through an optocoupler at all? Will I be able to make the otpocoupler work for both the Serial of a Teensy and a MIDI DIN connector?
I'm not an expert in electronics, I'm better at code, so I'd appreciate any help.
Thank you