Post by Pavan Bagwe

Open Card https://lnkd.in/d_QKv5DK I’m currently working on an open-source project called Open Card — an automated playing card dispenser combining mechanical design, electronics, firmware, and an app. Over the past few months: Designed parts on onshape https://lnkd.in/dDjc2377 and 3D-printed multiple mechanical iterations Tested, broke, and improved the mechanism Recently migrated from ESP8266 to ESP32 due to GPIO limitations Today we hit a small but meaningful milestone: the motor finally ran reliably — but not without lessons. Things that failed and what I learned: Burned a micro-controller by driving a motor with an NPN transistor without a flyback diode Learned (the hard way) how inductance stores energy and why motors behave nothing like resistive loads Switched to Schottky flyback diodes and proper switching topology Salvaged MOSFETs and diodes from old TV power boards and reused them successfully Understood internal resistance of 18650 cells, why low-ESR batteries + cheap hobby motors cause huge inrush current Used PWM + soft-start to control startup current and prevent brownouts Measured battery voltage vs duty cycle under real load, verified thermals, and validated that the power stage stayed cool — no simulations, only measurements. Next steps: Current sensing & protection Cleaning up documentation for open-source If you’re interested in embedded systems, power electronics, or open-source hardware, software, I’m happy to connect and learn together. #OpenSource #EmbeddedSystems #Electronics #Hardware

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