I am building a self playing piano. I daisy-chained 11 74hc595 shift registers to control (11*8) solenoids. (figure 1 only shows 1). The solenoids are rated at 2 Amps each. I use SPI from the arduino to bit bang data to get PWM over the outputs at about 20 kHz to make the keys play harder and softer. But only for about half a second until the key is pressed, then is sets it to 255/255. But even when I power a solenoid directly at 255/255 it is only capable of pressing the piano key 1 out of about 5 times. I think it doesn't always get the power it needs.
I thought it would be a good idea to add a parallel capacitor (C1) close to every group of 8 solenoids. But what would be a good capacitance?
[EDIT] I don't have a o'scope. I am using IRFZ44N Transistor N-Channel Rectifier Power Mosfets. 8 mosfets are grouped togheter (total 11 groups), the wires from my PSU to these groups are 18 AWG and ranging from 30 to 100 cm in length.
[EDIT 2] I added a gnd wire in the schematic between logic and solenoid side. I added 3 photos, pls dont judge the solder quality, its from 3 years ago. I also still need to do some wire management and actually fix the boards onto something because now they are just hanging there. I am currently testing with 47 uF, 220 uF, 470uF and 1000 uF. But dont see any difference so far. I also have a old (but still usable) car battery, would that be a better power supply?
