BLF BOT (Black Line Follower) – Construction Instructions

Circuit diagram

blfv3-1 blfv3-2

The boards are a shared project on OSH park.
Order from OSH Park


Software and programming Details are here



1x 1uF Ceramic Capacitor
1 x LIR2023 rechargeable 3.2V lithium button cell
1 x 20mm Button battery holder vertical
2 x QRE1114 (or QRE1113) IR proximity Detectors
2 x 8mm Disk Vibration Motors
2 x 1K 0.25W resistor
2 x 10K 0.25W resistor
2 x BC337 Transistor
2 x micro on/off switch
2 x small tooth brushes (you can cut these down so 2 tooth brushes can make 3 bugs)
1 x 8mm plastic bead
1 x 8pin DIP turned pin low level socket.
1 x PIC12F510 8pin DIP processor. (PIC12F508/PIC12F509 will work with some minor changes)

Total Cost ~ £5.50 each

This project uses Lithium Button batteries, please note the warnings here – Do Not short out the batteries, and Do Not swallow them.


20160506_163604 This is the TOP of the BLF PCB
20160506_164151 Add in the small blue tantalum capacitor and solder on the other side, cut off the spare wires close to the board.

Turn the board over

This is the BOTTOM of the BLF PCB

20160506_164259 Insert and solder (on the other side) the 8 way DIP socket, Ensure the small D cut out in one end of the socket, matches the one printed on the board. Ensure there are no blobs of solder connecting the pins.
20160506_16503620160506_165019 20160506_165030 20160506_165027

Insert the two infra-red sensors into the board.

Before soldering

Make sure that the small dot on each sensor is towards the middle of the board.

Ensure that the LEDs  in the sensor are both flush to the plastic housing and don’t stand proud. (If they do gently push them back in)

Also make sure that the sensors stand straight  up from the board and are at the same height from the board.

The bottom of each sensor should be at the same height as the top of the IC socket.

When all is straight and at the right height, carefully solder them in place.

If these aren’t at the same height and straight, your bug won’t function correctly.

20160506_165356 Solder in the two transistors flush to the PCB. cut off the excess wire on the solder side. Ensure there are no blobs of solder linking the legs of the two transistors.
20160506_165429 20160506_16562020160506_165538_001 Cut off one of the outer legs of the switch (as shown) and solder the remaining two legs into place flat and sideways on to the PCB
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Solder in the inner two 1K resistors

These will have a colour code of either

 Brown, Black, Red


Brown, Black, Black, Brown

20160506_170417 20160506_170426

Solder in the outer two 10K resistors

These will have a colour code of either

Brown, Black, Orange


Brown, Black, Black, Red

20160506_170625 20160506_170638 Insert the Battery holder flush to the PCB, you may have to bend the Capacitor a little towards the switch to get the bottom of the holder to sit flat to the PCB.
Solder  it in place on the bottom of the PCB being careful not to melt the IC socket.
20160506_171246 20160506_171303 Glue the red bead in between the two sensors. It needs to sit proud of the sensors by 1.5-2mm, you may need to file a couple of flats on either side to ensure it fits snugly between the sensors without bending them.
20160513_161807 Insert the Microprocessor.
Ensure that all of the legs have gone into their sockets. and that the D cut out matches the D cutout In the socket below.  If the legs are too wide to fit into the socket carefully push each side inline against a table top. Don’t try to move them one by one.
20160513_160057 20160513_160111

Taking the two tooth brush heads roughen the tops sandpaper and  glue on to the PCB

Ensure that both heads are flat and leave to dry

20160513_160122 20160513_160129

With the two vibration motors, solder the leads on to the top of the board only.

Un-peal the backing paper from the vibration motors and stick them to the flat plastic end of the tooth brush head.(not on to the bristles)

If you are happy with the position I suggest using a stronger glue to better affix the motors.



Make sure the switch is OFF

It should be towards the cut off leg

20160513_160941 Insert the battery, MAKE SURE THE + on the BATTERY is the same side as the + ON THE HOLDER 

Repeatedly stroke the bristles of the brushes towards the back of the bug. After a while they will stay at a slight angle pointing backwards.

Do this on both sides of the bug.

Continued in Running the BLF
Debug LED

An LED can be soldered  on to the spare pads (PL4) with a suitable series resistor.

The LED has the following cadences

. –       . – Right
– .       – . Left
.              Wait
–        –    Forward