MEP EP#338: Feature Complete or Minimal Viable Products

<h4><a href="https://macrofab.com/blog/mep-ep338-feature-complete-or-minimal-viable-products">MEP EP#338: Feature Complete or Minimal Viable Products</a><strong><br></strong></h4><p><strong>Project DiffProbe</strong></p> <ul> <li aria-level="1">Landed on the topology Stephen wants <ul> <li aria-level="2">High voltage dividers <ul> <li aria-level="3">Compensation capacitors</li> <li aria-level="3">CMRR calibration (120dB rejection)</li> <li aria-level="3">Offset correction</li> </ul> </li> <li aria-level="2">Buffers and Instrumentation Amplifiers</li> <li aria-level="2">Differential Stage</li> <li aria-level="2">10x and 100x attenuation means offsets have to be bang on</li> </ul> </li> <li aria-level="1">Opamps (3 of them) <ul> <li aria-level="2">Buffers <ul> <li aria-level="3">Low input bias current</li> <li aria-level="3">Low offset</li> <li aria-level="3">Bandwidth?</li> </ul> </li> <li aria-level="2">Differential amp <ul> <li aria-level="3">Low offset. Capable of driving 50 ohm load to the scope</li> </ul> </li> <li aria-level="2">Gain setting resistors <ul> <li aria-level="3"><a href="https://www.vishay.com/docs/28770/acasat.pdf" target="_blank" rel="noopener">Vishay ACAS 0612</a> - Precision resistor network</li> <li aria-level="3">4x0603 resistors to make a diff amplifier with a gain of 2 </li> <li aria-level="3">Relative tolerance of 0.05%</li> <li aria-level="3">Worst case relative temp-coefficient 15ppm</li> </ul> </li> </ul> </li> </ul> <p><strong>Project Snackey</strong></p> <ul> <li aria-level="1">Firmware is “feature complete”</li> <li aria-level="1">Display Commands</li> <li aria-level="1">How the vending motors actually work <ul> <li aria-level="2">INA219 Current Sensor</li> <li aria-level="2">Interrupts</li> <li aria-level="2">Improved method for next revision?</li> </ul> </li> <li aria-level="1">The one byte Serial Buffer problem <ul> <li aria-level="2">NEOPIXEL (WS2812) vs APA102 (SK9822)</li> <li