User manual

LPCXpresso Experiment Kit - User’s Guide

Page 76

Some have 1.25 – 1.75 ms as the range. Others have 0.75 to 2.25 ms. Note that it is not the actual

duty cycle that controls the position. It is the on-time. For a given/constant cycle period, there is of

course a direct relation between the on-time and the duty cycle. If the cycle period of 20 ms is chosen,

the duty cycle shall be varied between 5-10% and 7.5% represents the middle/neutral position. The

updatePWM() function must be updated to support 0.1% or even 0.01% resolution. 1% will be too

coarse. Also, the PWM block clock prescaler must be set to 19 (divide by 20) to handle the 20 ms

period.

Figure 44 – PWM Signal for Servo Control

See breadboard setup below. Note that an external power supply is needed to power the servo. 4-6

volt is a typical suitable level for a servo, but always check the datasheet for the specific servo that you

will be using. If you have soldered the components to the pcb, then there are three servo motor

connectors, J5, J6 and J8 (see page 5 on the schematic).

1-2 ms

20 ms

Left

Center

Right