D4E1 - DIY - Assistive Technology: 'Scale Aid 2018'

Introduction: D4E1 - DIY - Assistive Technology: 'Scale Aid 2018'

About: Student Product Design @Howest IDC Kortrijk

Veronique is a 36-year-old woman who is employed at "Het Ganzenhof" because
of her congenital syndrome (Rubinstein-Taybi). Here she takes on the task of helping to carry out recipes by weighing up quantities. This process has always been done by our client with the help of an ordinary kitchen scale. This kitchen scale carries several problems with it because Veronique doesn’t know any numbers or letters, can’t read and has thickened fingertips as a result of her syndrome. Due to this, our client always needed a helping hand by third parties during this process. So, the demand of creating a scale aid that allows Veronique to weigh quantities autonomously came from the setting itself.

Throughout the project, we focused on creating a brand-new scale that can be used within the kitchen. From our analysis we concluded that at least 3 elements must be present to ensure that a scale can be used, namely: an On/Off button, a Tare button and a display to determine how much already has been weighed. Especially the latter was a challenge within the project because our client has a lower mental age. Finally, we decided to use lighting symbols (upward red arrow – green thumb – downward red arrow) in our final prototype 1.9 to indicate how much has already been weighed.

Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

Step 1: Materials and Tools

In this step we will discuss all the materials we used.

Note: some knowledge of 3D printing and Arduino programming is usefull...



  • 2 x sheets of 2mm Polystyrene (600 x 450 mm)
  • sheet of 2 mm transparent PMMA (15 x 30 mm)
  • 10 mm Forex PVC sheet (15 x 50 mm)
  • black decal or sticker ( 50 x 50 mm)
  • red and green sticker dots
  • 6 x M3.5x12 csk screws
  • 2 x M2.5x35 csk self tapping screws
  • 6 x M3x12 nuts and bolts
  • self-adhesive dampers
  • PLA or PET-G 3d printer filament
  • CA glue
  • UV glue


  • Arduino Nano
  • mini usb cable
  • Load cell + glass weighing surface(5kg)
  • HX-711
  • 6 x 5V WS2812b leds
  • Power plug
  • 5V power adapter
  • 16x2 I²C lcd
  • Rotary encoder
  • big pushbutton
  • big rotary switch
  • female header pins
  • female - male dupont wires
  • 3 x 10K resistors
  • 220 ohm resistor
  • 3 x 1nf capacitors
  • 500 mA fuse
  • Perf board
  • Some Solder
  • Some thin wires


  • 3D printer (creality CR-10)
  • heat gun or hotwire
  • scissors and stanley knife
  • iron ruler
  • soldering iron
  • circular saw or band saw
  • table drill
  • holesaw 22 and 27 mm
  • cordless drill + drill set
  • some sandpaper (240 grit)

Step 2: 3D Printed Parts

For the 3D printed parts you will need a large printbed (Creality cr-10 300x300 mm) to print the sides in one go. You could also slice them into smaller parts and glue them together with CA glue, but for optimal strength it is recommended to print it in one piece.

The preferred filament to use is PET-G and as a second option PLA, both are foodsafe but PET-G is stronger and more durable to heat or direct sunlight.

You will need to print:

1 x side 1

1 x side 2

2 x indicator arrow

1 x indicator thumbs up

1 x lcd holder

2 x button spacer

1 x scale adaptor

6 x screw inserts

It is recommended to print at 0.2 mm layer height and with supports for the indicators, all other parts are printable without supports.

Step 3: Electronics and Software

Explanation of the used electronics

For the electronics we've used an Arduino Nano because of it's small size. The HX 711 load cell amplifier chip is connected to a 5kg rated load cell gathered from a cheap kitchen scale. The 5V ws2812b 60 leds/m ledstrip is used to indicate the amount to our patient, it is cut in 3 pieces of 2 leds. Then we've used a telemecanique button and rotary switch with the connecting blocks as a tare button and a on/off switch. The 16x2 I²C lcd is used to indicate the adjustable weight setting and actual measured weight. A rotary encoder is used to adjust the adjustable weight setting and reset it to zero if needed. Everything is powered by a 5V 500mA wall adapter with the corresponding power plug.


To prevent a wire mess as in the preceding prototypes we've used female header pins and dupont wires (male - female) to connect all the buttons and sensors to the Arduino. If something breaks it is easy fixable because of the modular design.

HX 711

  • VDD goes to 3.3V
  • VCC goes to 5V
  • Data goes to D2 of the Arduino
  • Clock goes to D3 of the Arduino
  • Gnd goes to ground

Load cell => HX 711

  • Red goes to red
  • black to black
  • white to white
  • green/blue to green/blue

Led strip

  • + goes to 5V
  • Data goes to D6 of the Arduino with a 220 ohm resistor inbetween
  • - goes to ground

Tare button

  • + goes to 5V
  • - goes to D10 with a 10K pull up resistor to ground

Power plug

  • + goes to the On/ Off switch with a 500mA fuse inbetween
  • - goes to ground
  • A 100nF capacitor parrallel to the + and -

On / Off rotary switch

  • one leg goes to the power plug with the fuse
  • the other leg goes to the 5V

Rotary encoder

  • Gnd goes to ground
  • + goes to 5V
  • SW goes to D11 on the Arduino
  • DT goes to D8 of the Arduino with a 10K resistor inbetween and a 100nF capacitor connected to ground
  • CLK goes to D9 of the Arduino with a 10K resistor inbetween and a 100nF capacitor connected to ground

16x2 I²C LCD

  • SCL goes to A5 on the Arduino
  • SDA goes to A4 on the Arduino
  • VCC goes to 5V
  • GND goes to ground


We've used the Arduino IDE to program everything...

To calibrate the load cell you will need to load the calibration sketch first onto your Arduino. It is easier to calibrate the load cell if you use an object with a known weight.

Once you know the calibration factor adjust it in the final code for the scale and load it to the Nano...

Further info is added in the comments of the code, once uploaded the coding part is done.

Step 4: Preparing the Assembly PART 1


Cut the sheets according to the plans shown above, we used a boxcutter and an iron ruler to cut straight edges.

Note: a sheetmetal shear works also to cut the sheets.

For the holes we used a small drill bit to predrill and a 22 and 40 mm holesaw mounted on the table drill with some clamps to drill the larger holes.

Sand with some 240 grit if needed.

For the folding surfaces we cut slightly along the line and heated the area with an adapted hotwire and a jig with an angle of 120°. This creates nice and clean folds. You could use a heat gun to fold the sheets, but you have to be carefull for wrinkling and overheating the plastic.


We used a 27 mm holesaw without the center drill bit on the table drill to make the dials.

Sand away the rough edges and be carefull not to cut yourself!

Lastly make the transparent acrylic more cloudy by sanding the surfaces with 240 grit.


We used the Forex sheets to make a sturdy base for the load cell and a mounting bracket for the PCB and leds.

Cut the 10 mm thick sheets acording to the sketches above and glue them together using CA glue.

Make a small indent on the 40 x 40 mm piece to accomodate for the load cell.

Predrill the holes according to your load cell and the bracket for the PCB.


Make 8 small hooks by glueing a 10 x 10 mm piece of 2 mm PS sheet to a 10 x 15 mm piece with CA glue. Space them evenly across the long side of the PS shell (third drawing). Two per side on the top surface and and one on each of the folded sidesurfaces. Glue them in place about 4 mm from the edge.

Step 5: Preparing the Assembly PART 2

Mounting the LCD Holder

Cut a piece of acrylic according to the outlines of the lcd holder. Drill 2 holes on each side close to the edge and through the acrylic and holder itself. Mount the lcd to the lcd holder using 4 x M3 nuts and bolts. Then mount the acrylic and lcd holder with lcd to the side piece using 2 x M3 flathead bolts and secure them with a nut.

Bottom plate holes

Glue the screw inserts to the angled sides of the top shell and space them equally. Now align the top shell with the sides and the base plate and trace the holes over to the base plate. Now drill them out using a 2 mm drill bit and chamfer them on the outside surface. Do the same thing for the PCB bracket holder.

Glueing the adapter plate ring

Glue the adapter ring to the glass weight bed of the scale using UV glue. Align it with the cutouts towards the indicator holes. Make sure the ring is slightly angled to make it flush with the scale, this is caused by the bending of the load cell.

Glueing tabs for the weighing surface

Make 8 7 x 3 mm tabs out of PS and glue them by 2. Next step is to glue them to the weighing surface, these need to be aligned with the cutouts of the adapter plate ring on 4 points. This is needed to secure the weighing surface to the scale.

Painting the 3D printed indicators

To prevent the 3D printed indicators absorb light, We've painted the inside of them in silver, so that they reflect the light of the leds.

Step 6: Assembly

  1. Mount the PCB in the bracket and secure it using the 2 x M3.5x12 screws
  2. Glue the load cell base, the pcb bracket and the led holder in place
  3. Connect everything to the PCB according to the Fritzing Schematic
  4. Mount everything in place :

The Tare button on the top surface with the button spacer inbetween and secure with the bracket screw

The On/ Off switch using the same procedure but on the side with the piece of the lcd holder

Stick the leds to the led bracket.

The rotary encoder to the side part using a nut and a washer to secure it and fasten the knob to the shaft

On the other side piece, add the power plug and drill out if necessary, secure it with the given nut

Lastly fasten the loadcell to the base and make sure it is level

5. Push the dial indicators trough the holes and sand away if needed, press the acrylic lenses onto the indicators

6. Slide the sides onto the base plate and snapfit the top shell into place

7. Screw the 8 M3.5x12 to the base plate securing the top shell and pcb bracket

8. Add the rubber adhesive dampers to the back of the base plate on the most critical bending points

9. Thread the the glass weighing surface and adapter ring to load cell

10. Add the weighing surface and align it with the cutouts

The assembly is done!

Step 7: Result

The Scale aid made it possible for Veronique to weigh ingredients by herself.

These indicators make it possible for her to comprehend what happens when she adds weight. The caretakers can adjust and reset the amount, with an instruction manual and some practice she can do these tasks totally independent. This is a big improvement over the weighing procedure she encountered previously.


Special thanks to: Veronique & "Het Ganzehof"

Project made by: Fiel C. , Jelle S. & Laurent L.

Be the First to Share


    • Trash to Treasure Contest

      Trash to Treasure Contest
    • Raspberry Pi Contest 2020

      Raspberry Pi Contest 2020
    • Wearables Contest

      Wearables Contest

    2 Discussions


    1 year ago

    Excellently documented, thoughtful project. Nicely done! :)


    Reply 1 year ago

    Thanks! :)