In my initial solenoid power board design, I used a PWM signal to control the power to the solenoids. I used an AND gate so that the PWM signal could be constantly running but require the microcontroller's command to turn on. This is done by putting the other pin on the AND gate to HIGH. I have added a PWM component to the single pulse generator so that I am able to control the average voltage of the pulse.
I am also trying to offload as much work as possible off the microcontroller so that it runs quickly. For most of the solenoids in the pinball machine, the power that is required will not change during the game. The only ones that I can think would possible change would be the pop bumpers. I would like them to be stronger during certain periods of play. To do this, I think I will need to use a 50V power supply in order to be able to play the game at a lower power level and then to have enough reserve to raise it to a noticeable difference. I have utilized the ever versatile 555 timer to produce the PWM signal.
To add the PWM generator to the circuit, I used the following:
TS555 - Low Power CMOS Timer
2x 1N4148 Switching Diodes
2x 1 nF ceramic capacitors
1x 10 KOhm resistor
1x 100 KOhm trim pot
1 x random ceramic capacitor for the control voltage pin
I tried using one of my IL766 optocouplers to provide the 12V required for my STP40NF10 MOSFETs to run at their full capacity but they are too slow. I checked the optocouplers' output with my oscilloscope and where the sharp drops in voltage were suppose to be, all I saw were gradual slopes. It did not even manage to drop the voltage 10%. The optocouplers worked on my old solenoid circuit because the PWM signal provided by the microcontroller had a low frequency. Unfourtunately, when applied to the solenoids, they make quite a bit of noise. I just need a frequency that is higher than what we can hear. Perhaps a small capacitor for high voltages could smooth out the voltage on solenoid side of the circuit.
EDIT: Checked the output of the MOSFET. The PWM portion of the signal seems to be getting through but I think the inherent capacitance of the MOSFET does not let it switch as fast as the PWM. So to reduce the time constant for the MOSFET, I changed out the large resistor I had connecting the gate to the ground with a smaller 2 KOhm.
I am also trying to offload as much work as possible off the microcontroller so that it runs quickly. For most of the solenoids in the pinball machine, the power that is required will not change during the game. The only ones that I can think would possible change would be the pop bumpers. I would like them to be stronger during certain periods of play. To do this, I think I will need to use a 50V power supply in order to be able to play the game at a lower power level and then to have enough reserve to raise it to a noticeable difference. I have utilized the ever versatile 555 timer to produce the PWM signal.
To add the PWM generator to the circuit, I used the following:
TS555 - Low Power CMOS Timer
2x 1N4148 Switching Diodes
2x 1 nF ceramic capacitors
1x 10 KOhm resistor
1x 100 KOhm trim pot
1 x random ceramic capacitor for the control voltage pin
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| The single pulse generator and the PWM generator providing a single pulse output with a controllable voltage. |
EDIT: Checked the output of the MOSFET. The PWM portion of the signal seems to be getting through but I think the inherent capacitance of the MOSFET does not let it switch as fast as the PWM. So to reduce the time constant for the MOSFET, I changed out the large resistor I had connecting the gate to the ground with a smaller 2 KOhm.
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