View attachment 96826
Here is partial schematic.
I'm triggering 555 from output of hall sensor. Then processing it and routing back to input of controller.
There isn't access to see what the hall circuit consists of, or the nature of controller input.
I do know that the hall pulls 9v input down to near zero.10k pulls the same input to 1/2. Giving an idea of the input impedance.
This circuit works fine when inserted in line between original hall sensor and controller. Logic after 555 not shown. That part works fine.
The problem I have is, connecting anything additional to hall effect output, stops the 555 from triggering.
There is a tachometer that needs to be connected to hall for setup.
R3 pull up is needed. I don't understand why, as hall out put makes full swing either way.
Tach has high impedance input. Even added a 47k right at hall output to keep from loading it. If I even connect 10' of 2C wire, the 555 following connection fails to trigger.
Tach is self powered and isolated. 9v battery
This circuit has a few issues...
Remove R3 (the resistor on the hall sensor is the only connection you need to the cap.
Change R1 to 1M. 10k is swamping out the signal from the high impedence (47k) signal and keeping the trigger high.
Change the cap that couples the Hall sensor to the 555 to 1 nF or 470pF range. Again, the high capacitance signal from the Hall sensor takes too long to drain the 10 nF cap and pulse the 555.
If the value of R4 can be changed, then I can suggest some different values. In any case, your current values do not generate a signal in my simulator.