Circuit Break - A MacroFab Podcast

MEP EP#287: Biased For Arduino

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MEP EP#287: Biased For Arduino

Bias Test System

  • Got the first board built and installed on an arduino
  • First tests were a success
  • Arduino library - works “first” time
    • Adien Akhmad
    • 2.5V reference voltage
      • MCP1501T-25E/CHY
      • 0.1% initial accuracy
      • 50ppm drift
      • I have measured a handful of these at work and have found the output to be within this range - 2.498
      • Arduinos and USB are noisy
      • Resistive measurements via constant current
        • Opamp driven constant current source
        • 1mA output current measured @ 1.001mA with a 1k resistor
        • Output current is somewhat load dependent - higher at higher resistance values
        • Possibly should have gone with a parallel opamp config
        • Validation
          • Voltages seem to be reading well.
          • 0 to 300V was within 1% of meter
          • Small “offset” reading
            • This is due to input buffer amp offset.
              • Datasheet calls out 125 as typical and 750 as max
              • I have seen the 100 to 400uV range
              • Will calibrate out
              • When doing a simple offset correction I can get 0.00000X readings
              • For resistive measurements there is a strange gain offset error
              • Verified the current and voltage but the readings to not match up
              • About 1.7% low for all readings
              • What is next
                • Finish validating the hardware with better standards and meters
                • Merge the scipi and ads1256 library
                • Make the gui
                • Profit

                  • Gripes about arduino

                  • When do you bite the bullet and fix a problem?
                    • Pin header
                    • Mounting holes
                    • Solution….
                      • Custom pin header
                      • Custom plastic “sled”

                        • Supply chain oddities

                        • Surprisingly Linear Tech devices are in stock but not Analog Devices?
                        • Working on that Linear Tech Automotive power supply design
                        • LT8672
                          • ...more
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