I built this MCU based infrared repeater to allow me to control my A/V equipment that is behind a wall. The system is very simple.
Power is supplied to CON1 from a cheap Alcatel phone charger that outputs stabilized 12V, passes through reverse voltage protection diode to IC1 that outputs 5V VCC. Atmel AVR microcontroller runs from 4MHz ceramic resonator Y1, C3+R1 form a reset circuit. Infrared detector (TSOP1738 in my case) is connected to INT0 input, C1+R2 are for detector power filtering. There is a green indicator LED D2 connected to PB2, and two 940nm infrared leds D1,D3 connected to PB3 via driver transistor Q1. R6 limits current through IR leds, and C2 is good to have if the IR diodes are at the end of long wires. I have separate board with R5,Q1,D1,D3,R6,C2 at the end of cable, but you may choose to build the whole circuit on single board and lengthen the wire that goes to detector.
The code is short and sweet, after initialization the interrupt handler takes care of everything - while the detector output is low, indicator led stays lit and a 39.2kHz burst of infrared is emitted from IR diodes.
; infrared repeater with AVR 90S2313 microcontroller
; Madis Kaal, mast@nomad.ee
.include "2313def.inc"
; port b pins
;
.equ LED = 2 ; indicator led (active low)
.equ IR_OUT = 3 ; infrared led driver (active high)
; port d pins
;
.equ IR_IN = 2 ; infrared detector (active low)
.set GIE = 7 ; interrupt enable bit in sreg
.def acc = R16
.def cnt = R17
.CSEG
.org 0
rjmp RESET ; Reset Handler
rjmp EXT_INT0 ; IRQ0 Handler
rjmp EXT_INT1 ; IRQ1 Handler
rjmp TIM_CAPT1 ; Timer1 Capture Handler
rjmp TIM_COMP1 ; Timer1 Compare Handler
rjmp TIM_OVF1 ; Timer1 Overflow Handler
rjmp TIM_OVF0 ; Timer0 Overflow Handler
rjmp UART_RXC ; UART RX Complete Handler
rjmp UART_DRE ; UDR Empty Handler
rjmp UART_TXC ; UART TX Complete Handler
rjmp ANA_COMP ; Analog Comparator Handler
EXT_INT1:
TIM_CAPT1:
TIM_COMP1:
TIM_OVF0:
UART_RXC:
TIM_OVF1:
UART_DRE:
UART_TXC:
ANA_COMP:
reti ; ignore interrupts that we dont need
;------------------------------------------
; invoked when IR receiver output goes low
;
; activates indicator led, outputs burst of infrared until
; the detector output goes inactive again, then turns off
; the indicator led
;
EXT_INT0:
push R0
in R0,SREG
cbi portb,LED
; output 39.2khz burst of ir while the input stays low
;
; 12.75uS
; ________
; ___| |_______|
;
irloop:
sbi portb,IR_OUT ; IR led on
rcall wait125
wdr ; kick the watchdog
nop
nop
cbi portb,IR_OUT ; IR led off
rcall wait125
sbis pind,IR_IN ; check the detector again
rjmp irloop ; and keep flashing the led if still active
sbi portb,LED ; indicator off
out SREG,R0 ; recover state
pop R0
reti
wait125:
ldi cnt,13
w1: dec cnt
brne w1
ret
RESET:
ldi acc,0xdf ; set stack to end of ram
out SPL,acc
; set I/O directions
; d2 input, rest of d is output
; b is output
ldi acc,0x04
out portb,acc
ldi acc,0xfb
out ddrd,acc
ldi acc,0xff
out ddrb,acc
; enable watchdog
ldi acc,0x1b
out wdtcr,acc
; enable INT0 interrupts on falling edge
ldi acc,0x42
out mcucr,acc
ldi acc,0x40
out gimsk,acc
bset GIE ; enable interrupts
; loop and kick the watchdog, waiting for interrupts to
; happen
mainloop:
wdr
rjmp mainloop