MEP EP#287: Biased For Arduino

<h4><a href="https://macrofab.com/blog/mep-ep287-biased-for-arduino/">MEP EP#287: Biased For Arduino</a><br></h4><h4>Bias Test System</h4> <ul> <li>Got the first board built and installed on an arduino</li> <li>First tests were a success</li> <li>Arduino library - works “first” time <ul> <li><a href="https://github.com/adienakhmad" target="_blank" rel="noopener">Adien Akhmad</a></li> </ul> </li> <li>2.5V reference voltage <ul> <li>MCP1501T-25E/CHY</li> <li>0.1% initial accuracy</li> <li>50ppm drift</li> <li>I have measured a handful of these at work and have found the output to be within this range - 2.498</li> </ul> </li> <li>Arduinos and USB are noisy</li> <li>Resistive measurements via constant current <ul> <li>Opamp driven constant current source</li> <li>1mA output current measured @ 1.001mA with a 1k resistor</li> <li>Output current is somewhat load dependent - higher at higher resistance values</li> <li>Possibly should have gone with a parallel opamp config</li> </ul> </li> <li>Validation <ul> <li>Voltages seem to be reading well.</li> <li>0 to 300V was within 1% of meter</li> <li>Small “offset” reading <ul> <li>This is due to input buffer amp offset. <ul> <li>Datasheet calls out 125 as typical and 750 as max</li> </ul> </li> <li>I have seen the 100 to 400uV range</li> <li>Will calibrate out</li> </ul> </li> <li>When doing a simple offset correction I can get 0.00000X readings</li> <li>For resistive measurements there is a strange gain offset error</li> <li>Verified the current and voltage but the readings to not match up</li> <li>About 1.7% low for all readings</li> </ul> </li> <li>What is next <ul> <li>Finish validating the hardware with better standards and meters</li> <li>Merge the scipi and ads1256 library</li> <li>Make the gui</li> <li>Profit</li> </ul> </li> </ul> <h4>Gripes about arduino</h4> <ul> <li>When do you bite the bullet and fix a problem? <ul> <li>Pin header</li> <li>Mounting hol