|
It does look as if the pulse train is produced by some logic device, possibly a micro, with a 5v supply - hence the 4.5 peak unloaded (5v less the driver Vdrop). The gauge reading is then derived from the pulse amplitude, possibly some sort of peak rectifier. Pretty hard to see how a signal fed back into the sender wire can do the job. The only thing I can think of is to put a dc level on the sender wire. ie If you stick 3.5 v on it, the pulse height will be 1v corresponding to the empty reading, stick 1.5V on it for 3v and hence full. You could do this by making something up that rectifies the variable duty cycle o/p of the LCD and turns it into these voltage levels. A sort of DAC with level shifting - probably an op-amp or two!
If you have a variable power supply it would be easy to try and see if what I say does actually work.
__________________
Sometimes I sits and thinks and sometimes I just sits.
|