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Microprocessoren lesson 6.PWM /motor control/servo

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PWM

Power control: Motor control Light Dimmer Servo control

Example applications PWM

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PWM 2

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PWM 3

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PWM 4Equations

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Summaryregisterspwm

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PWM 5setup

1. Configure the PWM pins P1A and P1B (and P1C and P1D, if used) as inputs by setting the corresponding TRISC bits.

2. Set the PWM period by loading the PR2 register.

3. Configure the ECCP module for the desired PWM mode and configuration by loading the CCP1CON register with the appropriate values:

• Select one of the available output configurations and direction with the P1M<1:0> bits.

• Select the polarities of the PWM output signals with the CCP1M<3:0> bits.

4. Set the PWM duty cycle by loading the CCPR1L register and CCP1CON<5:4> bits.

5. For Half-bridge Output mode, set the dead band delay by loading PWM1CON<6:0> with the appropriate value.

6. If auto-shutdown operation is required, load the ECCPAS register:

• Select the auto-shutdown sources using the ECCPAS<2:0> bits.

• Select the shutdown states of the PWM output pins using PSSAC<1:0> and PSSBD<1:0>bits.

• Set the ECCPASE bit (ECCPAS<7>).

• Configure the comparators using the CMCON0 register (Register 8-1).

• Configure the comparator inputs as analog inputs.

7. If auto-restart operation is required, set the PRSEN bit (PWM1CON<7>).

8. Configure and start TMR2:

• Clear the TMR2 interrupt flag bit by clearing the TMR2IF bit (PIR1<1>).

• Set the TMR2 prescale value by loading the T2CKPS bits (T2CON<1:0>).

• Enable Timer2 by setting the TMR2ON bit (T2CON<2>).

9. Enable PWM outputs after a new PWM cycle has started:

• Wait until TMR2 overflows (TMR2IF bit is set).

• Enable the CCP1/P1A, P1B, P1C and/or P1Dpin outputs by clearing the respective TRISCBits

• Clear the ECCPASE bit (ECCPAS<7>).

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Servo

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Servo 2

Controlled by sending a pulse of variable width Maximum and minimum pulse width to give

the angle (1.5 ms neutral position) Repetition rate (20ms) The pulse must repeated till angle is reached ,

after that to stay in that position it has to repeated too

< 1.5ms counterclockwise > 1.5 ms clockwise Pulse is generally between 1 and 2 ms Turn rate: time it takes from one position to

another. This can take seconds.

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Servo 3

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Servo 4

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Servo specifications

Control System: +Pulse Width Control 1500usec NeutralRequired Pulse: 3-5 Volt Peak to Peak Square WaveOperating Voltage: 4.8-6.0 VoltsOperating Temperature Range: -20 to +60 Degree COperating Speed (4.8V): 0.16sec/60 degrees at no loadOperating Speed (6.0V): 0.13sec/60 degrees at no loadStall Torque (4.8V): 76.37 oz/in. (5.5kg.cm)Stall Torque (6.0V): 94.43 oz/in. (6.8kg.cm)Operating Angle: 45 Deg. one side pulse traveling 400usec360 Modifiable: YesDirection: Clockwise/Pulse Traveling 1500 to 1900usecCurrent Drain (4.8V): 8.8mA/idle and 400mA no load operatingCurrent Drain (6.0V): 9.1mA/idle and 500mA no load operatingDead Band Width: 8usecMotor Type: 3 Pole FerritePotentiometer Drive: Indirect Drive Bearing Type: Dual Ball BearingGear Type: 3 Metal Gears and 1 Resin Metal GearConnector Wire Length: 11.81" (300mm)Dimensions: 1.59" x 0.77"x 1.48" (40.6 x 19.8 x 37.8mm)Weight: 1.94oz. (55.2g)

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Practical lesson 7

Choice 1 or 2 1.Write a program which turns over

the analogue value of a pot meter into the speed of an engine using PWM.

2. Write a program which turns over the analogue value of a pot meter into the position of a servo-engine using PWM..

Assignment 6