Home Chapter 13 Soldering the Parts into the H- Bridge Board
Soldering the Parts into the H- Bridge Board

In this activity, you will be assembling the H-bridge board and soldering the project. In order to solder, you will need to be very careful not to let your soldering iron sit for too long on the semiconductor parts, as these are sensitive to too much heat. You must get in and out immediately with your iron. This will assure you that you have not burned out the semiconductor part. Naturally, some parts are able to absorb more heat than others, but the best practice is to get the soldering joint done as fast as you can.

Generally, a semiconductor is more sensitive to excessive soldering heat than parts like resistors or wire, which can absorb more heat without damage .  

Parts Required


The white silkscreen printing on the circuit board allows you to understand where each component goes.

Soldering the Parts

  1. Plug in the soldering iron and let it warm up.
  2. Look carefully at the tip of the soldering iron and confirm that it is not black or discolored. It should appear to be a silvery color with no black on the tip. If there is black on the tip, then you must clean this with some fine grit sandpaper and “tin” the tip of the soldering iron by melting a thin coat of solder onto it.
  3. Another challenge with soldering is a cold solder joint (one in which an electrical connection has not actually been made, though it might look like it is) prevents the current from traveling from the wire to the solder and then into the electronic part.

 Another version of an H-Bridge that will work with the code provided. This can be purchased
from Hobby Engineering or other online sources. Another source is Sparkfun

     A good PDF construction guide to this driver can be found at SolarBotics in Canada.

    ENLARGED. This is a cross-section of the printed circuit board that shows a warm solder joint. Notice how the solder wicks into the copper traces, and then pull your iron away fast.


    ENLARGED.  Image of a cold solder joint. This may look like it is connected, but there may not be an electrical connection. You can use your multimeter to do a continuity test to determine if a connection does exist, but it is easier to solder well from the start.

  1. Start with placing the resistors in the board. Notice the board above supplied by Hobby Engineering and Sparkfun are similar parts to the lesson below. If you can see the silkscreen, then you are putting the resistors on the right side.



  1. Once all the resistors are placed, turn the board over and begin by placing the tip of the iron so it makes contact with the pad of the printed circuit board and the resistor lead . Then feed a small amount of solder in.
  2. Once you have soldered the resistors, cut the excess lengths of resistor wire off the backside as close to the board as possible without damaging the surface traces. Use your wire stripper cutter for this process.
  3. As you solder the parts, be careful not to create any solder pools (connections between the copper traces on the back of the board that were not intended) between pins. Use this opportunity of working with resistors that are not likely to be damaged with the heat of the soldering iron to practice doing your solder connections. It is a good idea to have a magnifier nearby to check all your soldering joints are up to standard.
  4. Turn your attention to stuffing the diodes into the board. Make sure to put each diode so the white/grayish ring (the cathode end) is closest to the white silkscreen line of the diode symbol. You may need small needle nose pliers, as sometimes the holes are a bit tight.

    Close-up of the diodes in the boar


  1. Now turn the board over and solder the diodes into the board one by one. Again, practice your soldering skills, but be more careful with the diodes in not letting the pins get too hot for too long. Semiconductors, as we know, can be heat sensitive.
  2. Clip all the wires one at a time on the back of the board.
  3. Next, place the 78L05 +5v voltage regulator in the board. This part looks like a transistor, but it is in fact an integrated circuit in a transistor package. Make sure the orientation of the 78L05 is aligned to the silkscreen mask. Remember that the BS2 board also has a 2940 +5v regulator on board as well.

    78L05 in board between the resistors

  1. Solder the transistor and clip the leads.
  2. Now place the capacitors into the board. These are non-polarized; so do not worry about the orientation. They are 0.01uF tantalum capacitors and they suppress transient voltages that could cause the L298 to malfunction.

     78L05 in board between the resistors

  1. Carefully place the L298 chip into the board. Check that all the pins are fully through the holes and not touching in any way.

      L298 H bridge

  1. Solder the L298 pin by pin. Watch that solder pools do not accidentally connect pins that should not be connected. I always inspect the board before and after to see if some pins have accidentally been connected. If they have you can use a bit of solder braid to lift the solder off the board or you can use a device called a solder sucker that will suck up the solder you do not want.

    Solder sucker (Smaller than actual size) by Jessica Miller


  1. Now, grab the motor power supply that you will be soldering to the board.
  2. Plug it into the wall and make sure the V+ and ground leads are separated.