- Blog entry posted in 'Electronics and Other Ramblings...', December 03, 2010.
- On power-up setup MCU for 40kHz PWM output on RB0,
- setup the SW UART for transmission at 1200bps on RB5,
- send RS232 “beam” character approximately every 33msec.
- On power-up setup TMR1 for 100msec,
- setup the HW UART for reception at 1200bps on RB2,
- monitor HW UART for reception of RS232 character,
- monitor RS232 for “beam” character,
- sample every 100msec for RS232 “beam” character,
- if “beam” character was received within the 100msec, turn off LED (or keep off, if previously off),
- “beam” character was not received within the 100msec, turn on LED (or keep on, if previously on).
So we presented a simple IR receiver/emitter pair here. What can we do with this? How about an example of a test bed where we can determine whether an IR beam is broken.
To do this two microcontrollers are used to control the IR emitter and IR receiver independently. Operation is obtained by sending a known RS232 communication (single character - "beam" character) through the IR link. The known RS232 character is sent three times within 100msec. If the receiver fails to receive any transmission within 100msec, the IR link (beam) is considered broken and an LED indicator reports this condition. This may be a bit of an overkill for a basic beam break circuitry, but it provides very good results.
The original beam break circuitry was built using a single microcontroller as shown below.
But using separate microcontrollers for the emitter and receiver allows to use any type of separation between the two. The following pictures shows the connections between the microcontrollers and the IR emitter and receiver.
Code Description – Beam Break Test Bed:
The code for this basic beam break test bed was created using Oshonsoft Basic. This language is not as complete or provides as much functionality as others (e.g. CCS C), but it can be readily obtained and used.
The emitter code can be summarized as follows:
The receiver code can be summarized as follows:
Code - Emitter:
Code:
'* PIC16F88 * IR Transmitter Test Bed *'
'Title: IR Transmitter
'Description: This program uses MCU to send an IR transmission.
'>>>>>>>>>>>>>IR transmission is sent by "ANDing" an RS232 character and a 40kHz PWM.
'>>>>>>>>>>>>>Transmission sent three times about every 100msec using the SW UART.
'Author: languer (2010)
'Pin Allocation:
'PIN# Main_Fn
'RA0 -> not used
'RA1 -> not used
'RA2 -> not used
'RA3 -> not used
'RA4 -> not used
'RA5 -> not used
'RA6 -> not used
'RA7 -> not used
'RB0 -> PWM Output
'RB1 -> not used
'RB2 -> not used
'RB3 -> not used
'RB4 -> not used
'RB5 -> RS232 IR output (SW_UART-RX)
'RB6 -> PGC - Programming clock
'RB7 -> PGD - Programming data
'Usage Information:
'Uses internal clock @ 8MHz
'IR Baud rate (SW UART): 600bps - 2400bps
'General Configuration
'for internal 8MHz
Define CONF_WORD = 0x3f50
Define CONF_WORD_2 = 0x3ffc
Define CLOCK_FREQUENCY = 8
OSCCON = 0x70 'define internal 8MHz clock
'Variable Declarations
Const trisa1 = %11111111
Const trisb1 = %01011110
Symbol io_pwm = RB0 'PWM output
Symbol io_tx232_ir = RB5 'rs-232 IR output
'wireless interface constants
Const beam_char = 0xaa 'RS232 transmission character
Dim _true As Bit
Dim _false As Bit
_true = True
_false = False
'Main Program
main:
WaitMs 3000
Call init()
While _true
Serout io_tx232_ir, 1200, beam_char
WaitMs 25
Wend
End
Proc init()
AllDigital
TRISA = trisa1
TRISB = trisb1
'pwm settings
'>>>pwm period to 40kHz
PR2 = 49
'>>>pwm duty cycle to 50%
CCPR1L = 25 'using 8-bit mode (for 10-bit mode, 100 would be written to CCPR1L:CCP1CON<5:4>)
'>>>pwm tmr2 prescaler 1:1 (for 40kHz)
T2CON.T2CKPS1 = 0
T2CON.T2CKPS0 = 0
'>>>pwm tmr2 enable
T2CON.TMR2ON = 1
'>>>pwm enable
CCP1CON.CCP1M3 = 1
CCP1CON.CCP1M2 = 1
WaitMs 1000
End Proc
Code - Receiver:
Code:
'* PIC16F88 * IR Receiver Test Bed *'
'Title: IR Receiver
'Description: This program uses MCU to detect an IR transmission. IR transmission is received by IR module, inverted, and then received by HW UART.
'Author: languer (2010)
'Pin Allocation:
'PIN# Main_Fn
'RA0 -> not used
'RA1 -> not used
'RA2 -> not used
'RA3 -> not used
'RA4 -> not used
'RA5 -> not used
'RA6 -> not used
'RA7 -> not used
'RB0 -> LED Output
'RB1 -> not used
'RB2 -> RS232 IR input (HW_UART-RX)
'RB3 -> not used
'RB4 -> not used
'RB5 -> not used
'RB6 -> PGC - Programming clock
'RB7 -> PGD - Programming data
'Usage Information:
'Uses internal clock @ 8MHz
'IR Baud rate (HW UART): 1200bps
'IR receiver idles "high", active "low"
'Version Info:
'v1
'->RS-232 IR receive
'General Configuration
'for internal 8MHz
Define CONF_WORD = 0x3f50
Define CONF_WORD_2 = 0x3ffc
Define CLOCK_FREQUENCY = 8
OSCCON = 0x70 'define internal 8MHz clock
'Variable Declarations
Const trisa1 = %11111111
Const trisb1 = %01011110
Symbol io_led = RB0 'LED output
Symbol io_rx232_ir = RB2 'rs-232 IR input
'wireless interface constants
Const beam_char = 0xaa 'RS232 transmission character
Const tmr1h_preload = 0x3c 'Timer1 preload for 100msec tick rate
Const tmr1l_preload = 0xb1 'Timer1 preload for 100msec tick rate
Dim _sample_received As Bit
Dim _true As Bit
Dim _false As Bit
_true = True
_false = False
'Main Program
main:
WaitMs 1000
_sample_received = 0
Call init()
'hwuart setup
Hseropen 1200
'preload tmr1 for 100msec tick rate
TMR1H = tmr1h_preload
TMR1L = tmr1l_preload
'enable tmr1
T1CON.TMR1ON = 1
'enable interrupts
INTCON.GIE = 1
INTCON.PEIE = 1
PIE1.TMR1IE = 1
PIE1.RCIE = 1
Dim _char As Byte
While _true
Wend
End
Proc init()
AllDigital
TRISA = trisa1
TRISB = trisb1
'tmr1 settings
T1CON.TMR1CS = 0 'tmr1 from internal source
'tmr1 prescale to div-by-4
T1CON.T1CKPS1 = 1
T1CON.T1CKPS0 = 0
Low io_led
WaitMs 100
High io_led
WaitMs 100
Low io_led
WaitMs 1000
End Proc
On Interrupt
'for tmr1 overflow
If PIR1.TMR1IF Then
'preload tmr1 for 100msec tick rate
TMR1H = tmr1h_preload
TMR1L = tmr1l_preload
If _sample_received Then
Low io_led
Else
High io_led
Endif
_sample_received = 0
PIR1.TMR1IF = 0
Endif
'for hwuart character in buffer
If PIR1.RCIF Then
Dim _char As Byte
Hserget _char
If _char = beam_char Then
_sample_received = 1
Else
_sample_received = 0
Endif
PIR1.RCIF = 0
Endif
Resume
rahila, December 08, 2010
sir, i think you can help me in clearing my doubts,may be foolishness, regarding propagation of waves... Its known that as the frequency of waves increases the distance it can travel also increases,then why do we need to keep two mobiles close to each other while sending datas through bluetooth technology... Is not bluetooth technology is using high frequency radio waves?
languer, December 08, 2010
Completely unrelated to the article, but i'll provide a quick answer. Actually it's opposite, the higher frequencies suffer more attenuation through distance of travel (because of their shorter wavelengths) - Friis equation should be a starting point for this. For bluetooth in particular; it has as much to do with frequency as it has to do with the very low transmit power - to meet regulatory requirements.
ripingz, February 20, 2012
[QUOTE=languer;bt362]Completely unrelated to the article, but i'll provide a quick answer. Actually it's opposite, the higher frequencies suffer more attenuation through distance of travel (because of their shorter wavelengths) - Friis equation should be a starting point for this. For bluetooth in particular; it has as much to do with frequency as it has to do with the very low transmit power - to meet regulatory requirements.[/QUOTE] what is ir beam function..i'm still dont get it.. why u give 2 transmitter circuit....
