Motor Controller Circuit and PCB Design
I was contracted to build a rotating speaker assembly for an amplifier company. The project as a whole is a multi-disciplinary effort, you can see more about the mechanical side of things here...
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Before printing, these circuits were prototyped on breadboards and protoboards. The circuit includes...
24VDC motor controller circuit.
5VDC microcontroller circuit used with amplifier foot pedal switch box.
Atmega88A chip
Adequate circuit separation via an optoisolator to mitigate any potential noise from the DC motor that may disrupt the microcontroller.
Two power supply circuits to convert from 120VAC. Each unit also has the appropriate EMC components to mitigate electromagnetic issues.
Factory calibration hardware so that a build tech can set the rotational speed of the baffle to specific frequencies.
1/4" TRS jack (Tip, Ring, Sleeve) used to integrate with foot pedal.
Embedded C Coding and Circuit Design
ATMega88A MCU embedded C coding was done using Atmel Studio. All code was uploaded and debugged via ISP using my Atmel ICE device.
Schematic creation and PCB layout was done in EagleCAD.
Button De-Bouncing
Two user buttons control the speed of the rotating unit. To have a responsive human interface I used interrupts to signal a change in duty cycle was required. Initially I didn't think about de-bouncing and I had incredibly unrelieable button sensing. Due to the switch bounce, the microcontroller was picking up on repeated interrupt commands.I implemented two button de-bounce solutions. In the hardware I added de-bounce capacitors, and in the software I used some time delays to check the input condition of my button pins to make sure the MCU only reacted to the stable button state.
Motor Noise and Observed Duty Cycle
Investigating the relationship between my PWM signal, observed motor duty cycle. My test circuit had a sharp response, and the duty cycle of my signal and the motor were very much alike. In my PCB I am observing capacitive tendencies within my MOSFET driver circuit which are effectively increasing the observed duty cycle.
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Additionally, I am attempting to reduce motor voltage ringing and motor noise with a change in PWM frequency.