Yes this is the start bit of any serial message.
I can do better than that and send you the oscilloscope traces.
Yellow trace on pin 2 , blue trace on pin 6 of the opto isolatior.
Sending Note on, 0x34, 0x60
Sending Note off, 0x34, 0x00
Note the voltage on the input to the LED in the opto is 1.96V because it is measuring the voltage across the IR LED when it is on. The output from the transistor, is 5V going to the RX input of the serial port.
Well not from the rise times of that signal. Pull up resistor is 680R in this case.
This is the reminder i have for myself.
You are the master on the matter here, so do you agree.
btw just the google search turns up a lot of hits for the H11L1 but i guess that one may be obsolete. Also in regards to the speed, a 6n138 is serious overkill. one of the reasons for picking 31250bps as a baudrate was so the parts would be relatively cheap and easy to come by (the other of course being that significant cable length could easily be supported even without the use of twisted pair or very low capacitance cables)
Well no actually, the baud rate was chosen to be what you get when you divide a 1MHz clock by 2, this gives you 500000 baud, but the popular hardware UARTS at the time required a clock signal 16 times the baud rate. So feeding the UARTS with a 500000 gave a baud rate of 500000 / 16 = 31250 bauds. So it was ease of build that governed the baud rate chosen. Which is why it is such a none standard speed.
Thanks for your circuits I will check them out on the scope sometime.
And a compromise, i was not talking about the actual figure but more about the rough idea. About 1ms per 3 byte command, ideally it would be faster but that would mean that the maximum length of the cables would be less.
