Laser Oche for Darts USB

I created this laser oche to replace my worn dart mat that had split and deteriorated from years of tripping over it and vacuuming around it. A solid raised oche would be a trip hazard, and tape just wasn't a suitable replacement for a proper throw line. This USB-powered laser projector provides a clear, visible line on the floor at the regulation distance without any obstruction or wear issues.

Hardware/Fasteners

1. 4mm diameter x 20mm long countersunk wood screws (x2) - for wall mounting
2. 2.87mm x 11mm long (9mm thread) pan head self-tapping screws (x4) - for assembly
3. M6 flange nuts (x2) - for tilt adjustment
4. M6 x 20mm long joint connector screws (x2) - for tilt mechanism

Tools Required

Essential

1. 3D Printer
2. Soldering iron
3. Screwdriver to suit wood screws
4. Screwdriver to suit self-tapping screws
5. Allen key to suit M6 screws
6. Tape measure
7. Wire cutters or knife
8. Heat gun (or hair dryer/paint stripper) for heat shrink
9. Multimeter - Critical for identifying USB wire polarity

Optional

1. Spirit level
2. Power drill and drill bits
3. Rawl plugs (for wall mounting)
4. Vernier calipers (for measuring drill bits, screws, etc.)

Electronics

1. Laser Module: Red Line Diode with Focusable Lens, 650nm, 5mW, 5V (12mm x 12mm x 40mm)
2. USB Cable: Any unused spare USB-A cable, approximately 1.2m long (depends on where you plug it in)
3. Solder: Light duty hobbyist solder
4. Heat Shrink Tubing: 6mm or 8mm diameter
5. Insulation Tape: Standard electrical tape

3D Printed Parts (PLA)

1. Total Weight: Approximately 78g
2. Total Filament: 9.88 metres
3. Total Print Time: 6 hours for all 3 parts
4. Print Settings:
5. Material: PLA
6. Infill: 20%
7. Layer Height: 0.2mm
8. Supports: Required in screw holes on base and box parts
9. Parts Printed:
10. Lid
11. Box/Housing
12. Base with tilt mechanism

Print the three components using the settings above.

See images for print orientation :

1. Lid - Print flat as shown
2. Base with tilt brackets - Print with brackets upright
3. Box/Housing - Print with the back face down

Important: Enable supports for the screw holes in the base and box parts to ensure clean threads.

Files Available: Download STL and STEP files from Thingiverse: https://www.thingiverse.com/thing:7251011

CRITICAL: USB cable wire colors are NOT standardized between manufacturers. You MUST test to identify positive and negative wires.

Understanding USB Pinout:

See the USB pinout diagram image - this shows the correct orientation when looking into the USB-A connector. Make sure you're viewing it the right way up, or pins 1 and 4 will be reversed!

The USB-A connector always has the same pinout when viewed correctly:

1. Pin 1 (rightmost): +5V DC - This is POSITIVE
2. Pin 2: D+ Data - Not needed
3. Pin 3: D- Data - Not needed
4. Pin 4 (leftmost): GND - This is NEGATIVE/GROUND

IMPORTANT: However, the wire colors inside your cable may be completely different from the diagram! Manufacturers use varying colors (black, orange, brown, blue, red, white, etc.). You MUST use a multimeter to identify which wire connects to which pin - never assume based on color!

Process:

1. Cut off the non-USB-A end of your spare cable
2. Strip back the outer insulation to expose the internal wires (you'll typically see 4 wires - my cable had black, orange, brown, and blue instead of the standard colors)
3. Use a multimeter to identify which wire connects to which pin:
4. Plug the USB-A end into a USB power source
5. Set multimeter to DC voltage (20V range)
6. Look at the USB-A connector carefully - refer to the pinout diagram image to ensure you're viewing it correctly (not upside down!)
7. Carefully probe each exposed wire while looking at the USB-A connector pins
8. The wire that connects to Pin 1 (rightmost pin) is your POSITIVE (+5V)
9. The wire that connects to Pin 4 (leftmost pin) is your NEGATIVE (GND)
10. You can verify by measuring voltage between them - should read approximately 5V
11. Mark or note which wires are positive and negative - write it down or label them with tape
12. Cut off the 2 unused data wires (the ones connected to pins 2 and 3) - you only need power and ground for this project

Safety First

Work in a well-ventilated area and avoid breathing solder fumes.

Process:

1. Before soldering, slide a piece of heat shrink tubing over the USB cable - long enough to cover your soldering area (you won't be able to add it after!)
2. Identify the laser wire colors:
3. Red wire = Positive (+)
4. Black wire = Negative (-)
5. Solder the connections:
6. Solder the identified positive USB wire to the laser red wire
7. Solder the identified negative USB wire to the laser black wire
8. Insulate the joints:
9. Wrap insulation tape around one or both of the solder joints to prevent shorts
10. Position the heat shrink tubing over both joints and the taped area
11. Apply heat using a hair dryer, heat gun, or paint stripper to shrink the tubing and make the connection electrically sound

BEFORE ASSEMBLY - TEST YOUR WORK

1. Aim the laser downwards at the floor or a safe surface
2. DO NOT look directly into the laser beam
3. Plug the USB cable into a power source (computer, USB wall adapter, power bank)
4. Verify the laser projects a line (not just a dot)
5. Check that the focusable lens rotates to adjust the line width

If everything works, proceed to assembly. If not, check your solder joints and wire connections.

1. Pass the laser diode through the hole on the underside of the box (the 12mm diameter opening designed for the laser body)
2. Route the USB cable through the cable exit port in the box
3. Roughly focus the laser by rotating the lens - don't worry about perfect focus yet, as the lens will rotate during this step
4. Position the laser so it sits properly in the housing
5. Attach the lid using the 4x self-tapping screws (2.87mm x 11mm)
6. Fine-tune the laser rotation by gently turning the lens through the lid opening to level the projected line horizontally

1. Slide the M6 flange nuts (x2) into the slots on the sides of the box housing - they should slide into the captive nut slots designed into the printed part
2. Position the assembled box between the two upright stays (brackets) on the base - the flange nuts should align with the holes in the stays
3. Insert the M6 joint connector screws (x2) through the base bracket holes and thread them into the captive flange nuts in the box
4. Don't fully tighten yet - leave them loose enough for adjustment. The M6 screws allow you to adjust the downward angle for aiming the laser

Positioning:

1. Measure 50mm (2 inches) below the dartboard center - this is where your laser oche unit will mount
2. Mark the mounting holes for the 2x countersunk wood screws
3. Optional: Use a spirit level to ensure the mount is horizontal
4. For solid walls: Pre-drill holes and use rawl plugs if needed
5. Mount the unit using the 4mm x 20mm countersunk wood screws

Regulation Distances (refer to diagram):

1. Dartboard center height: 5'8" (1.73m) from floor
2. Horizontal oche distance: 7'9¼" (2.37m) from wall/board face
3. Hypotenuse distance (laser path): 9'7⅜" (2.93m)

This is where precision matters!

Adjustment Process:

1. Plug in the USB cable to power the laser
2. Loosen the M6 screws on the tilt mechanism
3. Adjust the tilt angle downward until the laser line hits the floor
4. Use a tape measure to verify the hypotenuse distance of 9'7⅜" (2.93m) from the dartboard center to where the line hits the floor
5. Fine-tune the laser lens focus:
6. The focusable lens rotates the line as you adjust it
7. Get it roughly focused first
8. Make small adjustments to get a sharp, thin line
9. Rotate the lens slightly to ensure the line is perfectly horizontal/level
10. Once positioned correctly, tighten the M6 screws to lock the tilt mechanism in place
11. Verify the line is level - visually check that the line runs parallel to floor tiles/boards or other straight edges on your floor

Safety

1. Never look directly into the laser beam - even low-power lasers can damage eyes
2. Keep the laser aimed downward when testing
3. Ensure children understand not to look into or point the laser at faces
4. This is a Class 2 laser (5mW, 650nm) - safe for brief exposure but avoid prolonged viewing

Usage Tips

1. The USB power means you can plug it into a PC, laptop, or USB wall adapter
2. Cable length should reach your nearest USB power source - 1.2m is usually sufficient
3. Consider cable management - use clips or ties to keep the USB cable tidy
4. The laser is always-on when powered - use a switched USB hub if you want easy on/off control
5. PLA is suitable for indoor use but avoid direct sunlight which can soften the plastic

Maintenance

1. If the line becomes dim, the laser may be reaching end of life and should be replaced

Troubleshooting

1. No laser output: Check USB power connection, verify voltage with multimeter, check solder joints
2. Line is not level: Rotate the focusable lens slightly to adjust the line orientation
3. Wrong distance: Adjust tilt mechanism angle
4. Line too wide/narrow: Rotate the focusable lens
5. Flickering: Check for loose connections or poor solder joints

3D Print Files on Thingiverse: https://www.thingiverse.com/thing:7251011

Includes:

1. STL files (ready to print)
2. STEP files (for customization in CAD software)
3. Print orientation reference images