CBC Fundamentals Lecture is based on material from

CBC Fundamentals Lecture is based on material from Robotic Explorations: A Hands-on Introduction to Engineering, Fred Martin, Prentice Hall, 2001.

CBC Features Copyright Prentice Hall, 2001 2

CBC Sensor Ports Copyright Prentice Hall, 2001 3

CBC Digital Input 47 K for CBC digital port 15 K for CBC analog port WARNING: Mechanical switches BOUNCE!!!!! A few milliseconds. Copyright Prentice Hall, 2001 4

Digital Function Call Copyright Prentice Hall, 2001 5

Analog Input 47 K for CBC digital port 15 K for CBC analog port The 15 K resistor can be disabled!!! Copyright Prentice Hall, 2001 6

Analog Signals An analog voltage can take on any value between 0 and 3. 3 Volts. An Analog-to-Digital Converter (ADC) within the CBC, however, will quantize the analog signal. The CBC’s ADC is 10 bits wide. Copyright Prentice Hall, 2001 7

Quantization Copyright Prentice Hall, 2001 8

Sampling Theorm In order to avoid a non-linear phenomenon known as aliasing, an electrical signal must be sampled at a rate of at least TWICE the highest frequency component present in the signal. Fs > 2 * F h Copyright Prentice Hall, 2001 9

Complex Signals Complex signals (like square waves) are actually linear combinations of sinusoids. Copyright Prentice Hall, 2001 10

Bandlimiting Once a sampling rate has been determined, the input must be bandlimited. This means that the incoming electrical signal is filtered so that all frequency components above one-half the sampling frequency are removed! Copyright Prentice Hall, 2001 11

Analog Input Function Call Copyright Prentice Hall, 2001 12

Using Motors & Servos Copyright Prentice Hall, 2001 13

How do you connect motors to computers? • Computers operate at constant voltage and very low current • Motors draw high current and their speed and direction depends on the voltage • Robot controllers use: – H-Bridge circuit to handle current and direction – PWM to control speed Copyright Prentice Hall, 2001 14

H-Bridge Separate Logic Current from Motor Current SF 1 + SR 2 + V Motor SF 2 SR 1 Pulse On Copyright Prentice Hall, 2001 15

H-Bridge (reversed) Separate Logic Current from Motor Current SF 1 + SR 2 - V + Motor SF 2 SR 1 Pulse On Copyright Prentice Hall, 2001 16

Pulse Width Modulation • Pulse motor at fixed frequency – Maintains voltage level supplied to motor – Duty cycle governs speed Copyright Prentice Hall, 2001 17

Back EMF • XBC can measure EMF generated back from spinning motor • BEMF is proportional to actual motor speed from acroname. com Copyright Prentice Hall, 2001 18