how to choose resistor for LED.1) Check the voltage drop on led (
Vd)
2) Find out what will be the operating voltage (
Vs)
3) Decide how much we need current (it is selected on the power supply capacity, or the maximum output current of IC pin,and LED Imax)
IR=(Vs-Vd)/Iremarks
If the calculated resistance value non-standard should be taken nearest appropriate. (After you select you should recalculate current)
When LED work or heating it voltage drop decreases slightly sometimes it is necessary to take into account.
In my design, I take current value approximately equal to half of the maximum as LED is located very close to the photodetector, and no need for high brightness (less current will increase reliability).
In case of phototransistor is also possible to perform calculations on the basis of the manual but I do not know what model I have and what it features and is unknown to me consecrated created by DMM LED. So I just found right in experimental way.
I made HEX for you (speed 9600 standart settings) i test it with my software it work OK.
https://www.dropbox.com/s/qyisyfoqxdlw4gz/bu%2086%20uart.hex?dl=0circuit in attachments
value of R3 must be chosen experimentallyTo do this, run the COM Port terminal and view the data packets
end of package must always be the same is indicator of a well-functioning cable
01 11 be a1 fe fc 7c 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe fc e4 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe fc da 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe fc a0 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe fe fc 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe a8 be 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe 7e fc 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe 7e fe 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe e4 a8 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe e4 7e 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe e4 7c 01 00 be bf be be 04
00 86 86 86 86 80 possible terminal will display data like this
fc a0 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe fe fc 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe a8 be 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe 7e fc 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe 7e fe 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe e4 a8 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe e4 7e 01 00 be bf be be 04
00 86 86 86 86 80 01 11 be a1 fe e4 7c 01 00 be bf be be 04
00 86 86 86 86 80 so it can be difficult to understand if everything is okay