130-28176 Parallax Inc, 130-28176 Datasheet - Page 145

• Manufacturer Part Number: 130-28176
• Description: KIT PARTS PROCESS CONTROL
• Manufacturer: Parallax Inc

Specifications of 130-28176

• Accessory Type: Education Kit
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Board of Education Full Kit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

Chapter 5: High Current Drive and PWM Control
Earlier chapters discussed means to use transistors, standard or optical, to condition an
input signal for the BASIC Stamp. Equally important in process control is the ability to
drive large loads such as fans, motors, and heaters as actuators for the process.
The output of the BASIC Stamp is 0 V or 5 V and limited to 20 mA. The output voltage
and current are sufficient for driving small devices, such as LEDs, piezoelectric speakers
and integrated circuits. The output is not sufficient to drive larger loads directly, such as
small DC motors or very large 115 VAC motors, but with output drive interfacing, the
BASIC Stamp may very well be used for control of these much higher voltage and
current devices.
Even though the output of the BASIC Stamp is digital – on or off – there exist methods to
provide variable drive to devices. Examples include controlling the speed of a motor, the
energy output of a heater or the brightness of a lamp.
ACTIVITY #1: DC FAN ON-OFF CONTROL
The fan supplied with your kit is a brushless DC motor rated at 12 VDC and draws 0.09
amps (90 mA). The fan will operate with a lower voltage but will run slower and reach a
cutoff voltage around 3.5 VDC.
How can the 5 V, 20 mA output of a BASIC Stamp I/O control the fan? One means is by
using that wonderful device – the transistor. Recall that the transistor can be turned on
(saturated) if sufficient current is applied to the base to act as an electronic switch
controlling a much higher current as shown in Figure 5-1.
Figure 5-1
Bipolar Junction
Transistor (BJT)
Current Driver
DO NOT BUILD