Home Chapter 13 Practice using a soldering iron & Introducing the L298 H-Bridge Motor Driver
Practice using a soldering iron & Introducing the L298 H-Bridge Motor Driver


Parts required:

1 Soldering iron (25 – 35 watts is okay with a fine soldering tip)
1 Roll of standard rosin-core solder (.032-inch diameter)
 Wires that have been stripped for multiple practices
1 Pair of wire strippers

 

Warning! Solder is POISONOUS and must be handled with care. Never put this in your mouth, and always after handling wash your hands carefully. Also, make sure not to leave the solder around the house where children may have contact with the LEAD, which is a neurotoxin.

 

A standard 25-watt soldering iron is adequate for soldering solid-state parts, but make sure you get a fine tip for those extra fine parts. A temperature-controlled soldering iron is better, as it allows you to control the amount of heat that gets to the part.

 

 

   

 Common wire cutters and strippers These are also very common and can strip wires more by the gauge.

 

Plug the soldering iron in and make sure the iron is hot enough to melt the solder, but not too hot to damage the part. Have a wet sponge or wet paper towel available to wipe down the black oxidation that can build up on the soldering iron. The black carbon buildup will prevent the proper heat transfer to your part, and the moist sponge will help remove this and spread a thin layer of solder on the tip of the iron.

You can also use a fine piece of 200 grit sandpaper to lightly sand down the tip of the iron to remove unwanted black carbon buildup.

 

Warning! The soldering iron gets very hot and you must use this with caution. Do not touch the tip to any part of your skin under any circumstances.
Also, make sure not to let the iron contact the power cord, as this can melt the plastic sheathing and cause a short.

 

  1. The rule of thumb when soldering electronic parts is to leave the iron on the part (with good contact being made) for as long as you need to get the wire hot enough to melt the solder… but no longer. Remember that while wire is not too sensitive to too much heat other electronic parts are especially semiconductor parts like transistors and microchips. 
  2. Practice by stripping two wires and twisting the two ends of the wires together so that they will remain connected. Make sure you have a good mechanical
  3. Connection between the two wires.

    Make sure the iron touches both wires for proper heat transfer.

 

  1. Bring the iron in contact with the wire, and after about 1--2 seconds max feed the solder into the wire. You must always heat the part for a SHORT time first and then feed the solder into the area between the wire and the iron . The solder should appear to be absorbed into the wire, and this is a sign that you have a good connection.
  2. After you solder the wire, wipe your iron tip on a moist sponge to spread a thin layer of solder around the tip. This thin layer of solder allows proper heat transfer to the part you want to join.
  3. Practice this procedure on at least 4--5 pairs of wire until you feel comfortable with the process, at first heating the wire with the iron and then feeding the solder into the hot connection.

Solder and iron

 

 

Closeup of solder iron and tip

 

Figure 13-14 

 

Introducing the L298 H-Bridge Motor Driver

In Chapter 10, a gear head motor called a servo motor was capable of rotation of from 0-- 180º. Using the Pbasic code PULSOUT, you were able to accurately position the motor degree-by-degree, or swing from one rotation to the next.

In Chapter 11, you learned how to control the DC gearhead motor you will use in this lesson, and you varied the rotation from full stop to full speed and everything in between utilizing the Pbasic code PWM , but the ability to go to an exact position, as with the servo, was not possible with this circuit/motor and software control.

In this chapter, you will learn how to use DC gear head motors in association with a special device called an H-Bridge. The H-bridge allows you to change the direction of the voltage going to the motor, which means that you can change the direction of the motor dynamically. The use of an H-bridge opens up many possibilities in the control of robotic devices.

The L298 is a specialized solid-state H-bridge that allows you to control the direction of motors with the Stamp . The L298 that you will be using in this lesson is a versatile H-bridge controller that is capable of running two DC motors simultaneously -- forward and backward. This H-bridge has two input pins that allow you to stop one or two motors by sending the voltage of those pins to ground, which instantly disables the PWM output that is driving the motor.

The L298 motor driver is electrically isolated from the microcontroller, enabling it to handle a continuous current of two amps per motor and short surges of peak amperage as high as three amps. The motors that can be controlled by an H-bridge use between 6--35 volts DC .

 

Pinout of the L-298 motor driving H Bridge