Quote: Originally Posted by pippolippi
I'm not too sure: looking at the characteristics for the hef family, the minimum input voltage is -0.5V, the max low input (at 15v) is 4V (probably 3.5 at 12v) and the minimum high input is 11V (probably 9V at 12v).
With this characteristics I think it makes no difference connecting the HU to the serial port directly or through the buffer: if the level coming from the HU is critical to interface directly to a serial port I think it'll also be critical wrt the hef4050b input. OTOH the levels coming from a "real" serial port (+12,-12) are outside the lower limit (-0.5v)
I think a simple diode could take care of that...
Quote:
and a laptop/usb probably won't have enough voltage to drive it high.
Maybe the best solution is to use a max232 and the buffer.
Well, to keep simple, the solution of the comparator (LM234) proposed my Mox would probably be better suited. Power it with 12V, enter your serial port Tx with a diode on a positive input and the set the threshold of the negative one with a divider bridge. (e.g. 47K/10K to get a threshold around 2V - but the diode causes an offset). You could even put a 100K potentiometer to be able to adjust the threshold.
Any comment is welcome.