So I designed a circuit. It is controlling a pulsating actuator-solenoid. I used a power BJT as shown in attachment. Now I have a problem. As you can see all 4 circuits are in parallel. As a consequence, all 4 solenoids have one lead in common. When I test each subcircuit, it works fine. You can see in the attachment a picture of my circuit. Left 8 leads are going to potentiometers. Each potentiometer is controlling one solenoid. As I said, when only one solenoid is connected it works fine, I can adjust the speed of pulses as I desire. But when I put all 4 solenoids, and turn on the circuit something bizarre happens. If they are all at the same frequency, ergo all pots are at same level, they pulsate ok. But when I change one of the solenoids frequency, it shuts off(that solenoid). Others stay the same, but of course other 3 are at the same frequency. It doesn't pulsate slower nor faster. As if my circuit does not withstand multiple frequencies. Am I making some obvious mistake? Can this circuit be modified, or are there any other circuits for this mechanism to work? Idea is to control the flow of water. Valve opens and shuts and that controls how much water is sprinkling. Those pots are controlling the speed of those impulses. I used 555 timer to do this.