'NE555 P' Reset pin problem

[vinodquilon]

I have set up the 555 astable MW to generate AF signals as shown in the attachment.
The intended function is that When StD control signal goes logic HIGH AF signals are permitted
to appear at + output. When StD is logic LOW, AF signals get suppressed at output.

But in practical when StD is LOW, AF signals not suppressed at output.
So I manually connect 4th pin to GROUND, then the signals get suppressed at + out.

So I am going for an OR gate as a replacement of Q4 & R9. One pin is always LOW, other one
connected to StD control.

Does have any idea about the problem ? I think Q4 open condition doesn't bring GROUND
condition at active low RESET pin.

Attachment- https://www.scribd.com/doc/27308469

 

[IanP]

Does have any idea about the problem ? I think Q4 open condition doesn't bring GROUND condition at active low RESET pin.

Force pin[4] to the GND level by adding a resistor betweeen [4] and GND ..
It's not the best way of switching [4] by npn BJT, but should work ..

Rgds,
IanP