Take me to the Steps

Working LEGO Phonograph

I have built a series of Lego phonographs, but none as successful as this model. Based on an arm design by Jose Pino and using a Lego WeDo motor and the Scratch programming environment, my friends and I built a phonograph that played a record loudly enough to be heard across the room with no amplifier needed: just a nine ounce plastic drinking cup serving as the horn!

This particular phonograph is build from the programmable Lego WeDo Kit. The motor speed is programmed in Scratch, which interacts with the phonograph through a USB hub. You, of course, might already have all the bricks needed to build the phonograph and can purchase the Lego M-Motor and Lego USB Hub separately. This phonograph is by no means high-fidelity but provides the tool to play records from the $2 bin or other vinyl you do not mind damaging as you experiment with building Lego and programming in Scratch. You can use this phonograph to play records recorded at 33 1/3, 45, or 78 RPMs because the motor speed is controllable by the program you write!

LEGO Phonograph Materials

Materials

  • Vinyl record that you do not mind damaging
  • Lego WeDo Kit Design ID 9580
  • Lego Base Plate
  • Lego USB Hub Design ID 9581

For the turntable:

  • Lego Power Functions M-Motor Design ID 8883
  • Lego 2×6 brick
  • Lego Cross Axle 3M Design ID 4519
  • Lego Bushing (2) Design ID 6590
  • Lego Technic Gear 24 Tooth Design ID 3648
  • Lego Cross Axle 8M Design ID 3707
  • Lego Technic Gear 24 Tooth Crown Design ID 3650
  • Lego 2×6 plate (2)
  • Lego 1×2 brick (6)
  • Lego Wheel 81.6 X 15 Design ID 2903/6596
  • Lego Technic Wedge Belt Wheel (Pulley) Design ID 4185/70162

For the arm:

  • Lego 2×6 brick (3)
  • Lego 2×4 brick (4)
  • Lego 2×8 plate
  • Lego 2×6 plate (2)
  • Lego Technic, Axle and Pin Connector Design ID 3651
  • Lego Connector Peg/Cross Axle Design ID 6562
  • Lego Technic, Pin Connector Plate 1x2x1-2/3 Design ID 32530
  • Lego Turntable 2×2 plate
  • Lego Cross Axle 12M Design ID 3708
  • Lego Cross Axle Extension 2M Design ID 59443
  • Lego Cross Axle 10M Design ID 3737
  • Lego Technic Lever 3M Design ID 6632

For the horn:

  • Fine grit sandpaper
  • Sewing needle
  • 9oz. plastic drinking cup
  • Foam, cut into wedge and small square shapes such as Darico Foamies Foam Marshmallows
  • Rubber band
  • Paper towel or napkin

About the Author

Josh Burker works with elementary age students on constructivist technology projects at an independent school in Connecticut. He has been a Lego maniac since kindergarten.

Photos by Meghan Scheck

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Project Steps

Construct the turntable.

Insert Cross Axle 3M into Lego M-Motor. Place Lego bushing on axle, followed by the Lego Technic Gear 24 Tooth.

Connect M-Motor to 2×6 brick. Connect M-Motor to base plate.

Place Technic Gear 24 Tooth Crown at one end of Cross Axle 8M with teeth facing upwards to mesh with Gear 24 Tooth.

Assemble stabilizing element on the base plate, next to the M-Motor and Gear 24 Tooth.

Use the Lego 1×2 bricks and the Lego 2×6 plate to build the rest of the stabilizing element.

Top the Axle 8M with another Lego bushing.

Place Lego wheel 81.6×15 at top of Cross Axle 8M to act as the turntable.

Connect M-Motor to USB Hub.

Construct the arm.

Stack three Lego 2×8 bricks.

Stack four Lego 2×4 bricks, connect to 2×8 bricks.

Connect Lego 2×8 plate to top of stacked bricks.

Stack two Lego 2×6 plates, then connect them to the top of brick stack.

Place WeDo Turntable 2×2 plate at center of 2×6 bricks.

Place Connector Peg/Cross Axle in top hole of Pin Connector Plate.

Connect Axle and Pin Connector onto Connector Peg/Cross Axle, connect to WeDo Turntable 2×2 plate.

Connect Cross Axle 12M to Lego Cross Axle Extension 2M.

Connect Cross Axle 10M.

Connect Technic Lever 3M to end of the arm.

Connect arm to Axle and Pin connector.

Build the horn.

Use sandpaper to sharpen the end of the sewing needle so it will fit into record grooves.

Pierce bottom of plastic cup with sewing needle. Push needle through small square of foam.

Push the needle through the hole in the bottom of the cup, sharp end pointing out.

Double- up the rubber band and place around base of cup. Use rubber band to connect cup to Technic Lever 3M.

Insert wedge of foam between the cup and the Technic Lever 3M to angle the cup.

Put paper napkin in the base of the cup, mindful not to dislodge the needle.

Attach arm/horn assembly.

Attach arm assembly to Lego Base Plate. Make sure your record fits and does not touch the arm assembly. Move the motor and turntable assembly if necessary.

Put the record on the turntable.

Place the record on the turntable wheel. Center the record over the Cross Axle 8M as best you can.

Secure the record by placing the Lego Technic Wedge Belt Wheel (Pulley) on top of the record.

Program scratch.

Connect the Lego USB Hub to your computer.

Open Scratch. From the Control Blocks, add a When (Flag) Clicked block and a Forever block. Connect these blocks.

From the Motion Blocks, add a Motor Direction (That Way) block and a Motor Power block. Put these two blocks inside the Forever block.

Conclusion

Experiment with the motor speed. On my turntable I was able to get close to 33 1/3 RPM with a motor speed of 22. You can adjust the motor speed as the turntable turns by changing the motor speed value and pressing Return on your keyboard. In Scratch, click the Flag to start the motor. Place the needle on the record and listen to the music! If the needle makes a high pitch squeal, try adjusting the angle of the needle. You might have to cut a differently angled piece of foam. You want the needle just shy of being perpendicular to the record. If the needle skims across the record, sharpen it more. Time to head out to the record store to find some more records in the $2 bin!