I am trying to trigger an scr/thyristor from a 0-5V TTL pulse (channel 1 on the oscilloscope output). The schematic can be viewed below. I am using the TTL to pull the 2n2222 transistor 'on' which than triggers the p-chan. mosfet allowing current to flow to the gate of the scr. Both the mosfet and transistor are biased by a floating 5 volts power supply from the 'wall'. To test that the scr is open, I have added another floating 16 volt power supply with resistor to measure a voltage drop across. The problem is that when I have the two grounds of the power supply's isolated I get ringing and wild oscillations (seen in figure 1). When the two grounds are reference to each other (seen in figure 2) the output of the scr than goes from low to high, and I would expect the voltage to go high to low.
Note that the channels 1,2,3 correspond to the measurement points 1,2,3 in the schematic and ground#1,2 refer to the different grounds of the power supplys. Any advice would be awesome thanks!