User manual

LPCXpresso Experiment Kit - User’s Guide
Page 42
Copyright 2013 © Embedded Artists AB
Figure 14 – Breadboard Connections for SW2, SW3 and LED
Another output device, besides a LED, is a buzzer. A buzzer outputs a single frequency tone when
driving current through it. A PNP-transistor is controlling the current through the buzzer. Pulling the
base of the transistor low will enable the current through the transistor (and hence the buzzer). The
series resistor on the transistor’s base connection limits the current (since signal GPIO_7-BUZZ will be
close to ground, 0V, when pulled low by the LPC111x and a PNP bipolar junction transistor’s emitter-
base voltage is fixed to around 0.7V).
Figure 15 – Buzzer on Schematic Page 4