Embedded Systems Programming Custom sensors for the use with Atmel ATmega8535 microcontrollers

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Embedded Systems Programming

Custom sensors for the use with Atmel ATmega8535 microcontrollers

and the Kanda STK200 board

Designed by Richard AnthonyUniversity of Greenwich

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New sensors for the ATmega8535

Embedded Systems Programming II Richard Anthony, Computer Science, The University of Greenwich

Light Sensor

Connects to Analogue input ADC7 (pin 7 of Port A)

Reading increases as light intensity increases

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Floor-Switch Sensor

Connects to Digital input (bit 0 of any port)

When the mat is stepped on, the switch operates

4



Passive Infra-Red (PIR) Sensor


When a person moves, in detector range, the internal switch operates

5



Magnetic-Switch Sensor


When the magnet is moved in / out of range, the switch operates

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Twin Variable Resistor Sensor

Connects to Analogue inputs ADC2 and ADC3(bits 2 and 3 of port A)

Rotating the dials changes the analogue resistance values

77Embedded Systems Programming II Richard Anthony, Computer Science, The University of Greenwich

Peripherals – Thermistor (2)

Our custom temperature sensor can be connected to bit 6 of port A.

(Must be used on port A because it is an analogue device and needs to be sampled using the ADC).


Peripherals – Thermistor (2)

Digital value (reading most significant 8-bits from 10-bit ADC)

708090

100110120130140150160170180190200210220230240

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

Temperature (degrees Celcius)

AD

C o

utpu

t val

ue

Thermistor temperature sensor probe calibration (8-bit values read as ADCH, i.e. most significant 8 bits)

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Peripherals – Humidity Sensor

Our custom Humidity sensor can be connected to bits 3, 4, 5 of port A (uses all three bits).

(Must be used on port A because it is an analogue device and needs to be sampled using the ADC).


Peripherals – Sounder

Used in PCs, Christmas cards, alarm clocks ….

Low output current needed - can be driven directly from a parallel port pin.

Our custom sounder device is connected to bit 3 of the port.

You need to configure the pin for output and provide a pulse on the port bit 3.

See the Loudspeaker demonstration project provided.


Peripherals – Motor with shaft encoder and H/W Interrupt generation

MotorCan be driven via bit 3 of any port (‘1’ provides power to the motor).

Primarily designed for PWM using Timer/Counter0. Timer 0 Output Compare Match Output OC0 is the alternate function of Port B bit 3.

Motor can reach speeds exceeding 100 Revolutions per Second (6,000 RPM).

Motor stalls if driven with a duty cycle less than 29% (approximately 8 RPS).

Shaft EncoderComprises a ‘Slotted-Opto Switch’ (which detects when its light beam is broken) and a rotor with four cut-outs, enabling detection accuracy of ¼ rotation (i.e. 90 degrees).

If measuring rotational speed, four pulses represent 1 revolution.

The output of the Slotted-Opto Switch is connected to bit 2 of any port.

Primarily designed to generate a Hardware Interrupt INT0, which is the alternate function of Port D bit 2.



Connections to Port B and Port D

Motor

Rotor

Slotted Opto

Switch



Motor

Rotor

Slotted Opto

Switch

Transistor driver

circuit for motor


Peripherals – Shaft encoder

Infrared light beam

IRLED

IRsensitive transistor

(under rotor)

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There is also a simpler motor rig that does not have the optical feedback system

Details will be added soon


Digital Signal Processing – D-to-A conversion with a resistor ladder

A simple 8-bit R-2R resistor ladder(connects to any port, uses all 8-bits configured as outputs)

Converts a Digital value in the numerical range 0 – 255 into an Analogue value in the range 0 Volts to 5 Volts

Resistors

8 Analogue outputs, one per stage to

allow experiments

Bit 0

8 bit Digital data input

Bit 7



Oscilloscope Earth connection


Peripherals – Accelerometer and X-Y axis Bar LEDs

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Peripherals – Accelerometer and X-Y axis Bar LEDs



Output device - SERVO

Converts a control signal from a single digital output port pin into a precise rotational position (angle).

PWM is used to generate the control pulse width in the range 0.5ms – 2.5ms (1.5ms pulse indicates the ”neutral“ / central position).

Rotation: 180 degrees.

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Peripherals – Servo adapter board


To Microcontroller

port

To Servos

Power (from supply) 5Volt to 6Volt

Ground from supply (0Volt)

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To Servo

Signal (PWM pulse)

Power 5Volt to 6Volt

Ground (0Volt)


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Two servos connected, using both Timer1 PWM

channels

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Peripherals – Servos in use (simple 2-servo robot)

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Peripherals – InfraRed receiver (RC5 command receiver, as in TV remote controls)

InfraRed receiver

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RFID reader

Peripherals – Radio Frequency Identification (RFID) reader

“Tag read”Indicator LED

RFID tag


Peripherals – KeypadProvides a simple means of numerical data or control input. The Keypad has 12 buttons arranged in a 4 Row * 3 Column Matrix:

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The LCD provides a versatile means of displaying alphanumeric data and messages (such as error codes, status messages, and user instructions).

The LCD can display 2 rows of 16 characters.

LCD display panel

Peripherals – Liquid Crystal Display (LCD)


Peripherals - Seven Segment display

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Embedded Systems Programming Custom sensors for the use with Atmel ATmega8535 microcontrollers

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