TerryS wrote: > I didn't find the datasheet for the toslink transmitter part used in the > Wandboard, but the datasheets for similar parts I did find didn't look > like the resistor affected the LED current at all. It is just a digital > input turning on and off the LED. The LED current is not adjustable. > > TerryCorrect, all TOSLINK transmitters that I know about take a standard digital input and have a builtin LED driver circuit. I don't know of any that bring the LED pins out directly. That 22.2 ohm resistor is just a standard thing used to slightly cut down the rise time of the signal to cut down on ringing when driving a load.
The cap between VCC and GND is important, but I'm not as sure about the necessity of the ferrite bead. BTW for removing stubborn parts on boards you might want to ChipQuik solder. It is sold for removing SMD parts but it works just as well for through hole ones as well. It is a solder with a super low melting point, melt blobs of it over the pins and keep the iron moving between blobs, it will dissolve the original solder and stay liquid long enough for you to pull the part off. After you get the part off use solder wick etc. to make sure you get all of this off the board before soldering a new part. This having it wrong on wandboard just reinforces my findings, there is a curse on TOSLINK transmitters. I have NEVER put one on a board that turned out right the first time. Including the SWAMP05. I know it's going to turn out wrong so I quadruple check the spec sheets to make SURE I get it hooked up right, and it still turns out wrong. And here the wandboard guys did it as well. It's got to be a curse. We can do 314 pin monster connectors right, 900 pin cpus right, but these simple little 3 terminal devices confound us all. It doesn't make sense. Actually I think it's the spec sheets. The one for the part on SWAMP05 has a table that says pin 3 is ground, and the schematic shows pin 1 connected to ground. Another I looked at shows the pins being labeled 1 2 3 in line on the physical drawing, but when listing the functions in a table they list 1 3 2. If you are not VERY careful in reading this you can get it backwards. It's sloppy spec sheets that I think are at the root of the curse. But it's sort of nice to know that I'm not the only one to have this problem. John S. ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=97881 _______________________________________________ discuss mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/discuss
