Hello, I'm a beginner here and lifelong tinkerer, and I've recently begun the dream of starting my own business. It's all happened fast, and there have been many bumps along the way, but now I'm up against a problem that I desperately need help solving. Any input is welcome.
I make a product that has a normal PWM speed control that operates a 12v DC brushed motor at up to 0.5 amps, and is speed adjusted via built in knob. Direction is controlled via a DPDT switch in the motor leads. The problem is that there is no soft start or stop built into the speed control, and now I've found that my product requires both. Without them, the abrupt start or stop causes big problems, and my product is being justly criticized at this point.
I do not have room in the machine itself to change speed controls (it was designed around this one to the mm), and very little room to add much circuitry but it's conceivable. The solution I've been pursuing is by designing a foot pedal in the 12v power supply leads that when pressed, will perform the soft stop and again will soft start (approximately 4 seconds of ramp time). So in my mind, the foot pedal needs to slowly reduce or increase the input power from 0v-12v after pedal press. I did some research on "soft starting dc motors" and found a couple of diagrams that showed a mosfet being used in conjunction with a small 1uf capacitor and pair of resisitors. If this is applicable, it would be perfect to be small enough to fit into my foot pedal. However, I have no idea of the values needed, and I have my doubts that a slowly charging and draining capacitor would affect the output of a mosfet (because it's a switch and can only reduce output effectively by being switched via a pwm signal). And this would be cascading transformers since a similar circuit is in the internal speed control.
I also came across a reference to a 555 based sensing circuit solution but want to keep it as simple and small as possible. I wish I could express how important this is to me, having just made the leap into self employment and trying to get my business off the ground. If anyone can help guide me to a solution, I'd appreciate it.
Thank you,
David