Welcome to the weight matching prop. Here we will explain what the prop does and how to make it.
You need to have minor electronics skills and you need to know how to program and Arduino.
The prop uses a load cell (scale) to detect weight. Players have to match the right weight by placing the correct object on the scale.
Now, this is just the inside of the prop so you would need to build the actual prop to match your theme. The scale doesn’t need to be visible – you can put something else on top of it to act as the container the players put things in. Using the load cell we reference below, the total weight of on the cell has to be less that 5 KG.
You can read the instructions and watch this video to see the prop in action and then we will move on to talk about building it.
If you don’t want to build this on your own, you can buy a completed control box for $150 (shipping to US included) from us. You still need to buy the load cell listed in the parts list below. If you are interested in this please contact us.
First, you need to go shopping! Here is the parts list.
These are Amazon affiliate links – I get a commission if you use them to buy the parts. You don’t pay anything extra.
Assuming you have nothing on hand, you need to buy all of this. If you are already into building props then you may have some of these things laying around already.
- $ 8 Arduino Nano
- $ 5 USB Cable
- $ 5 Screw terminals for Nano
- $ 6 Relay board
- $11 NeoPixel Lights (You only need a single pixel, but this is the smallest thing you can buy)
- $ 9 Buttons (You only need one red and one black)
- $10 Load Cell
- $ 7 Ribbon Cable
- $ 3 Screw Terminals (Couldn’t find this on Amazon so this is a link to Digikey)
- $ 8 Box to put it all in (Couldn’t find this on Amazon so this is a link to Digikey)
What is a job with no tools!
- Philips screw driver
- Soldering iron
- 5/26 drill bit
- 3/32 drill bit
- Exacto Knife
- Hot glue gun (optional)
- Speed square
- Double sided mounting tape
The first set of steps is to prepare the box by drilling holes etc. Take a look at the final inside and outside of the box to get the general idea of where we are headed. Notice these holes:
- Small hold on top for NeoPixel wires
- Holes for screw terminals (not visible)
- Holes on side for buttons
- Hole onside for USB to Arduino
- Remove all 4 stand-offs in the cover and the base (best done by grabbing with pliers and twisting)
- The hole for the USB cable will be done after the Arduino is placed to ensure alignment
- Holes for switches: drill a 5/16 hole on the left and right side of the cover ½ inch from the short side and centered on the height of the cover
- Hole for NeoPixel: drill a 3/32 hole on the face of the cover – aligned with the holes for the red and black buttons, ½ inch left of the center of the cover
- Use a speed square to draw a line across the face of the cover that is 1” below the switches
- Place the screw terminal on the line and make a mark at each leg of the screw terminal
- Drill a 3/32 hole at each mark
Get all the parts in the box and ready to connect.
- Install the switches – red on the right when facing the outside of the cover
- Use 2 layers of mounting double stick to mount the Arduino tight against the center posts and centered left to right – ensure the side with the A terminals faced the middle of the box
- If your Arduino has 6 pins sticking up on the side away from the USB connector, they need to be cut off as they are to high to fit in the box
- Now that the relay is mounted, its a good time to use a drill bit and exact-o knife to cut a hole in the cover that will allow the USB cable to be connected to the Arduino.
- Use 2 layers of mounting double stick to mount the relay tight against the center posts and centered left to right – orientation does not matter
- Peel 8 inches of 3 conductors from the ribbon cable
- Solder to the pads of the NeoPixel (Must be on the input side of the Pixel)
- Thread the wires down through the hole for the NeoPixel and stick the NeoPixel to the outside of the box
- Push the screw terminal into the holes drilled – its usually tight enough it stays in place on its own
Wiring the Cover
Now its time to connect everything together.
When viewed from the INSIDE with the legs of the screw terminals away from you, the order of the screw terminals from left to right is:
NC COM NO GND DAT CLK +5
- Cut 8 inches of 9 conductors of ribbon cable, strip and tin both sides of all conductors
- Tin all the legs from the screw terminals
- Tin all legs on the switches
- Cut the 5V and GND wires from the NeoPixel to be just long enough to reach the corresponding screw post with a little slack
- Use one of the just cut pieces of wire to connect one leg of one switch to one leg of the other switch and leave a lead long enough to reach the GND screw terminal post
- Connect the center two wire of the ribbon cable – one wire to the open leg of each switch
- Connect the rest of the ribbon cable wires to the screw terminal pegs left to right – one wire to each peg
- NOTE: When connecting the GND peg, also attach the GND from the NeoPixel and wire that is connected to both switches
- NOTE: When connectign the +5 peg, also attach teh +5 from the NeoPixel
- Optionally – hold all the wires (don’t forget the one long one from the NeoPixel) flat against the cover and secure with hot glue to provide strain relief – don’t pile the glue to thick or it will be a problem later)
Wiring the Relay
You’re almost there! Just a few more easy steps to go!
The input side of the relay will have labels something like +5(vcc), Trig and GND.
- Cut 3 conductors of ribbon cable long enough to reach from the input side of the relay to the furthest away of either GND or A0 on the Arduino
- Strip and tin both sides of all 3 conductors
- Connect one conductor into each screw terminal on the relay input side
- Connect the conductor that goes to Trig to A0 on the Arduino
- Leave the other 2 unconnected for now
- Connect the COM, NO and NC wires from the cover to the corresponding screw terminal on the output side of the relay
Wire the Arduino
Your pretty much in the home stretch here. This part is pretty easy as long as you stripped and tinned all the wires.
Screw the wires from the cover into the appropriate Arduino terminal:
- A1 -> Black Button
- A2 -> CLK Screw Post
- A3 -> NeoPixel wire
- A4 -> DAT Screw Post
- A5 -> Red button
Programming, Testing and Final Touch
Ok, now for the fun part!
Grab the Arduino code from our GitHub (the one called WeightPuzzle) and program your Arduino.
You may want to label the screw terminals. When viewed from the OUTSIDE with the screws further away from you, the order from left to right is:
+5 CLK DAT GND NO COM NC
Connect the scale (you need to build a wire harness, or cut the end off the one that comes with it) to the +5, CLK, DAT and GND terminals and your scale is ready to use!
Here is that link to the instructions again in case you missed it in the beginning 🙂
Now that you read all this, if it sounds like a bit more than you want to do, remember that we will make a control box for you for $150 (shipping to US included) from us. You still need to buy the load cell listed in the parts list. If you are interested in this please contact us.