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Difference between revisions of "Multimeter Negative Probe Holder"

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Revision as of 02:09, 9 November 2019

MOST Delta filament as guide.JPG This page was part of an MTU course MSE4777 OA and MSE4777 OB/MSE5777/EE4777/EE5777: Open-source 3-D printing

Please leave comments using the discussion tab. The course runs in the Fall semester. It is not open edit.

The first functional iteration of the balance.

This tool is used to hold the negative probe when reading voltages on motor control boards for the Athena2 3D printer. It could be modified to fit another printer setup. The model was created using FreeCAD.

Understanding the market

Things lacking from this design that are to be improved upon:

  • There is a lot of unnecessary plastic. This can be cut down to improve cost savings.
  • The OLED display is similarly costly. A serial connection or an LCD will suffice.
    • A serial connection also allows data logging.
  • There is no built in calibration process; this can be integrated pretty easily.

The first prototype of this balance has 0.1 g precision (on a 5000g load cell) with no averaging. This has not been tested for accuracy yet, but is promising assuming that the load cell is linear. The first prototype (printed bed, base, cover, microcontroller, buttons, and load cell/amplifier) cost around $22 dollars, and has precision that competes with this $120 device.

Project goals

  1. Generate a low-cost 3-D Printable Balance
  2. Allow for use of multiple load cell styles
  3. Implement a calibration sequence
  4. Allow data logging


OpenSCAD files and Arduino firmware are located on GitHub.


  1. Arduino Nano micro-controller
  2. HX711 load-cell amp
    • Can be powered using a digital output pin on the Arduino - current cost is only 1.5 mA, while the Arduino can provide 20 mA.
  3. Load Cell
    • TAL 220 - Implemented
    • TAL 221 - Designed, but not implemented.
  4. LCD Display

3-D Printable Parts

  1. Base
    • Slot for access to Arduino Nano's micro-USB
    • Spot to hold Nano and HX711
    • Accepts half of supported load cells
    • Holds LCD (if present)
  2. Bed
    • Accepts mass to be measured
    • Accepts second half of supported load cells
  3. Breeze cover
    • Helps prevent airflow from affecting measurements.

Load Cells

Spec sheets are easily located on Sparkfun

Software Functions

  1. Turn on
    • Set up serial
    • Set up display (if present)
    • Set up load cell
    • Read calibration from EEPROM
  2. Tare
    • This is already built into the HX711 Library for Arduino
  3. Calibrate
    • Accept a known mass
    • Determine a new sensitivity, accounting for tare/offset
    • Save the new sensitivity value into EEPROM
  4. Measure
    • Show current value in kg on LCD and over serial


OpenSCAD files and arduino firmware are now on GitHub.