2017-01-01

Assembling a Laser Trap

This post shows how to assemble a laser trap from parts. If you want to know how the trap is designed, read Designing a Laser Trap. If you want to know how it can be used, check out Laser Trap: Dexterous Escape.


The following tools are useful to have during the assembly of a laser trap. Soldering iron, tin solder, flux, tweezers, nippers, toothpick (for the flux), microscope, Blu-Tack, permanent marker and a FTDI USB TTL serial cable.

You need some experience at soldering to be able to put together a laser trap. Some of the components are quite small and can be difficult to handle for a beginner.

Main Board

The following parts are needed when assembling the main board for a laser trap.

1x Main PCB
1x 75Ohm resistor, 0.1W, 0603 package (R1)
1x 1uF ceramic capacitor, 0603 package (C1)
1x 1.8V LED, 0603 package (D1)
1x HM-10 Bluetooth LE Module
1x LDO regulator 3.3V, SOT-223 package (U1)
2x 1x3p female connector
1x 9V battery connector
1x Steel stripe



Start by applying flux to the pads for R1, C1 and D1. This will make the components stick a little and you avoid having to chase the components around the board with the soldering iron. Place the components on the pads and solder them in place. Note that D1 have polarity and should be placed with the cathode pointing towards R1. The polarity is marked on the back with a T. The top side of the T is the cathode. (This is a bit strange as all guides on the net say the opposite, but the diode I am using, HSMH-C190, has its marking reversed.)


Put a small amount of Blu-Tack on the back of HM-10 and put it in place on the Main PCB and solder it to the seven pads. If you have Main PCB R1 (without revision marking) you only need to solder one of the four ground pads on the lower side. If you have a HM-10 module without USB as the one in the image, you don't even have pads for two of the ground connections.


Put U1 in position and solder the three legs and the heat sink in place.


Insert the leads from the 9V battery connector into the holes below U1 and solder them in place. Black is ground and should be soldered to the hole out in the corner of the PCB.

If you have Main PCB R1 you need to cut the copper trace that connects the two outer pads in the lower 3p connector. You should then connect the lower pad to one of the spare ground pads next to HM-10.


Put both 1x3p female connectors in position and solder them in place.

Mark the top side of the board as shown in the image.


Connect a 9V battery or another power source between 4.8V and 15V. The LED should start to blink. Attach a USB TTL serial cable to the serial terminals and exchange the following request response sequence at 9600-8N1.
   AT+MODE1
   OK+Set:1
   AT+NAMELASERTRAP
   OK+Set:LASERTRAP

The trap is now ready to connect to the Android application.


For lasers that draw more than 30mA the voltage regulator needs to be cooled more efficiently than what the PCB alone can manage. Attach the steel stripe with Blu-Tack on the opposite side of U1. This stripe is also useful for mounting the trap and sensor in the correct position to monitor the laser beam.


Sensor Board

The following parts are needed when assembling the sensor board for a laser trap.

1x Sensor PCB
1x 1x3p male connector, 90 degree angle
1x 1.3kOhm resistor, 0.1W, 0603 package (R1)
2x 1x1p male connector, straight
7x Photo resistor


Start by applying flux to the pads for R1. Place the component on the pads and solder it in place.


Insert the two photo resistors at the top and the two photo resistors at the bottom into the mounting holes. Cut the leads and solder them in place.


Remove the pins from the two 1x1p male connector and put the remaining plastic tubes on the outer legs of the right and left photo resistors as support. Insert the three center row photo resistors into the mounting holes. Cut the leads and solder them in place.

Put the 1x3p male connector in position and solder it in place.


Red Laser

The following parts are needed when assembling the red laser for a laser trap.

1x 1x3p male connector, straight
1x Red Laser Module
2x Shrink tubes
1x Steel stripe
1x Copper bracelet
1x M5 bolt
1x M5 nut

Green Laser

The following parts are needed when assembling the green laser for a laser trap.

1x Driver PCB
1x 1x3p male connector, 90 degree angle
1x 200Ohm resistor, 0.1W, 0603 package (R1)
1x BC807 PNP transistor, SOT-23 package (Q1)
1x Green Laser Module
1x Steel stripe
1x Copper bracelet
1x M5 bolt
1x M5 nut

Laser Trap

The following parts are needed when assembling a laser trap.

1x Main Board
1x Sensor Board
1x Red or Green Laser

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