e005012.pdf

AUDIO &VIDEO

RC5 Sleep Timer

Everything off!

Design by U. Reiser

The well-known ‘sleep’ function in clock radios and television sets switches

off the equipment after a preselected time. However, what good does it do

to put the television into standby mode while the stereo set or DVD player

that is connected to it remains unaffected? The sleep timer described here

sends standby codes to several RC5-compatible devices at the same time.

Function and operation

The circuit shown in Figure 1 allows you to

select the equipment that will be switched on

or off as well as the sleep time, which might

better be called the delay time. The sleep

timer is operated using four pushbutton

switches. The current state of the timer is

indicated by four LEDs, each of which corre-

sponds to 30 minutes of time delay.

In normal operation, these diodes

are enabled for only one second out

of every ten, in order to save energy.

When the ON button is pressed,

pin 4 (MCLR) is pulled from a high

level to a low level. This resets the

processor, which consequently

wakes from the sleep mode. After

the switch-on pulse, the series of

LEDs runs through all possible dis-

play states and ﬁnally remains in the

state corresponding to a delay of

two hours. The sleep time count-

down starts at this point.

The operating status indicator D6

is active as long as switch S4 is

pressed. The weaker the light from

this LED, the lower the battery volt-

age. Red LEDs should be used for D1

through D4, but D6 should be a

green or yellow LED. The higher

voltage drop of the latter type makes

it considerably easier to recognise a

drop in the battery voltage than with

the red LEDs used for the time scale

display.

Pressing the DOWN button (S1)

activates the LED scale, which

shows the current delay time for

slightly less than three seconds. If

this button is pressed for longer than

0.75 second, the delay time is

reduced by half an hour every 0.75

second. If it reaches the minimum

time, it jumps back to two hours.

When the DOWN button is released,

the time delay begins, and the dis-

play scale remains lit for another two

seconds.

Naturally, the sleep timer can con-

trol equipment only if it is pointed at

the infrared receiver(s) of equipment

in question. In order to ascertain the

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AUDIO &VIDEO

best location for the sleep timer, you

can press the TEST button (S2),

which causes the selected standby

signals to be transmitted. This also

interrupts the sleep time counter.

Pressing the OFF button (S3) puts

the PIC controller into the sleep

mode (not to be confused with the

sleep delay time of the circuit!). At

ﬁrst the display scale will show the

current delay time, and then it will

count down to zero at an interval of

0.3 second. Following this, the half-

hour LED blinks ten times at a rate

of 5.5 Hz, and the timer then

switches off.

Any desired combination of

equipment that should be switched

off by the sleep timer can be

selected using five jumpers. The

television set is always included in

the group to be switched off.

D 5

100n

2 h

47µ

16V

RB0

RB1

RB2

RB3

RB4

MCLR

IC1

0h5

D 6

RA1

PIC16F84

-04/P

BT1

RA2

RA3

1 h

2x 1V5

RB5

RB6

RB7

RA4

RA0

1h5

OSC1

OSC2

3k9

***

4MHz

BC547

DOWN

TEST

OFF

see text

* voir texte

zie tekst

siehe Text

000026 - 11

Generating the RC5 codes

Figure 1. Circuit diagram of the RC5 sleep timer.

The RC5 signal is generated by

means of several timing loops that

set or clear RA0. Since the shortest

timing interval (one instruction time)

is 1 µs with a 4 MHz clock, the tim-

ing differs slightly from the RC5

standard. The times generated by

the PIC are marked on the timing

diagram shown in Figure 2 . Every

RC5 instruction consists of 14 bits. A

logic 1 (rising edge) is generated by

the calling CALL LO and then CALL

HI in sequence, while a logic 0

(falling edge) is generated by revers-

ing the calling sequence. Bits 6

through 10 form the device address.

In addition to the two Start bits, the

Control bit is always a logic 1. The

Control bit is used to distinguish

between multiple presses of a but-

ton (or contact bounce) and an optical

interruption of the light beam. It

changes its logical state each time a

button is pressed, for which reason

it is also called the toggle bit. How-

ever, since the equipment is

switched on by the ‘normal’ remote

control and switched off by the sleep

timer, it is not possible to correctly

specify the value of the Control bit in

the sleep timer. This does not hurt

anything, as long as the last instruc-

tion sent by the normal remote con-

trol unit was not ‘switch on from

standby’. Even in this case, the

chance of failure is only 50%, since

this only happens if the Control bit

was a 1 the last time it was sent. By

the way, this is also the reason why a

RC5 receiver sometimes cannot

recognise 11, 12 and so on when the

instruction comes from an adaptive

remote control unit.

000026-11 ), or as a ready-programmed PIC

(number 000026-41 ). The program flow is

shown in Figure 3 . The subroutine named

INITIALISATION sets the five bits of Port A

as outputs and the eight bits of Port B as

inputs, sets the prescaler ratio to 1:256 and

connects it in front of the RTCC. At the same

time, the pull-up resistors for all leads of

Port B are activated. Immediately after the

power supply is switched on or a reset

occurs, the routine POWER-ON-SELF-TEST

drives LEDs D1 through D4 sequentially for

0.3 s each. This process is intended to indi-

cate that the circuit is basically in good work-

Software description

The sleep timer is controlled by the

program SLEEP.ASM. This is avail-

able via the Internet from www.elek-

tor-electronics.co.uk , from our Read-

ers Services on a diskette (number

14 bits

25.074

64 bits = 114.624 ms

111 011111000

1.791

14 bits = 25.074 ms

1 t p = 7

3 tp = 21

32 x 4 tp = 896

000026 - 12

Figure 2. Timing diagram of the RC5 signals generated by the PIC.

5/2000

Elektor Electronics

AUDIO &VIDEO

initialisation

on is extended by two seconds. If

this button is held for longer than

0.75 second, the program jumps to

the subroutine CHANGE-SLEEP-

TIME. This routine reduces the sleep

time by half an hour every 0.75 sec-

ond, or changes it from 0.5 hour to 2

hours. This process continues until

the DOWN button is released.

The TIMING routine, which is

located next and in two subsequent

places, decrements the counter that

controls switching the delay time

scale LEDs on and off. In addition, it

counts down the counters for the

seconds, minutes and half hours of

the overall running time. If the scale

power-on

selftest

set

start value

check

DOWN -sw

scale

> 0.7 s

DOWN -sw

change

sleep time

timing

check

TEST -sw

transmit

IR tv1

check

jp 1

check

jp 2

check

jp 3

check

jp 4

check

jp 5

transmit

IR vcr

transmit

IR sat

transmit

IR dvd

transmit

IR cd

transmit

IR combi

keys

off

timing

COMPONENTS LIST

check

OFF sw

clear

scale

flash

sleep

Resistors:

R1 = 10 Ω

R2-R6 = 1k

Ω

R7 = 10k Ω

R8 = 3k

timing

Ω

000026- 13

Capacitors:

C1 = 47µF 16V radial

C2 = 100nF

Figure 3. Flow chart of the RC5 sleep timer software.

ing order. The routine SET-START-VALUES

loads the starting values into a series of

counter registers that are used for blinking

the delay time scale at a 10-second interval

and for the 4 hour to half an hour time delay

process. After this comes the main program, in

the form of an endless loop consist-

ing of six other routines. The first

action is to poll the DOWN switch. If

it is set, the delay time scale is illu-

minated for two seconds. If the scale

is already on, the time that is stays

Semiconductors:

D1-D4 = low-current LED, red

D5 = low-current LED, green

D6 = LD271 or SFH485 with

reﬂector

T1 = BC547

IC1 = PIC16F84-04/P,

programmed, order code

000026-41

000026-1

Miscellaneous:

X1 = 4MHz ceramic resonator

(Conrad Electronic #50 31 69)

S1-S4 = miniature pushbutton, 1

make contact, 6 ⋅ 6 mm 2 for

board mounting (Conrad

Electronic #70 04 60, Bourns

#7906H-001-000, Farnell #535-

916)

10-way pinheader, plus up to 5

jumpers

Toko handheld transmitter case

(Conrad Electronics #52 43 44)

Battery holder for 2 ‘Micro’

batteries

PCB, order code 000026-1 *

Disk, order code 000026-11 *

* Price and ordering information

on the Readers Services pages

elsewhere in this issue.

off

test

down

IC1

000026-1

Figure 4. Circuit board track and component layouts for a circuit board that ﬁts in the

recommended remote control enclosure.

Conrad Electronics are at

http://www.conrad-electronic.com

Elektor Electronics

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AUDIO &VIDEO

generates the RC5 codes and the

processor finishes its job with a

Sleep instruction.

If the overall running time has not

timed out, the TEST button is next

polled. If it is pressed, the RC5 code

for TV1 is sent first. After this,

jumper JP1 is polled. The code for

VCR1 may then be send, depending

on the jumper setting. The same

process is repeated for the other four

jumpers.

The TEST routine can exit via the

KEYSOFF subroutine only after S2

has been released. This means that

only one infrared signal output can

occur each time the button is

pressed, which increases the life of

the batteries. The TIMING subrou-

tine is now executed once again.

The following routine, CHECK-

OFF-SWITCH, monitors the state of

the OFF switch S3. If this is pressed,

the delay time scale is visually

decreased from its present value to

0.5 hour, and LED D1 then blinks ten

times. After this the program stops

early with a Sleep instruction.

If the STOP button is not

pressed, the TIMING rou-

tine is executed once

again, and the program

then jumps back to testing

the DOWN button.

1.5 mA. The pulse code of the RC5

signal is amplified by transistor T1

and passed to the IR LED. Two 1.5-V

batteries are used as the power

source. According to the manufac-

turer, the PIC will work down to a

voltage of 2 V, but in our tests it still

worked at a voltage of 1.8 V. This

means that you can milk the very

last milliwatt-second out of the bat-

teries. With a supply voltage of 2.5 V,

the current consumption of the RC5

sleep timer is 1.22 mA with the scale

diodes on and 0.4 mA when they are

dark. In the PIC sleep mode, it is

only 30 µA.

Table 1. Equipment codes

Jp Device

VCR1 (video recorder 1)

CD (compact disc player)

DVD (compact video disc player)

SAT1 (satellite TV receiver 1)

Combi (stereo set)

mounting height of the pushbutton switches

should be adjusted to match the key caps.

Five holes must be drilled in the enclosure for

the 3-mm LEDs. Their mounting height is also

important. The 5-mm IR LED protrudes

through a hole at the top of the enclosure and

is connected to the circuit board by flexible

wire. In the lower part of the enclosure, there

is a battery compartment that can hold two

penlight cells (AAA) with a battery clip. You

can also use mignon cells (AA), but without

a clip.

Packaging

Although the printed circuit board

for the sleep timer shown in Figure

4 is one-sided, switches S1 through

S4 and LEDs D1 through D5 are

mounted on the copper side of the

board, so that that the controls and

indicators are all on one side of the

board. The remote control enclosure

suggested in the components list

already includes four key caps. The

(000026-1)

Hardware

With the use of a PIC

processor, the number of

components for the circuit

is kept to an absolute min-

imum. A 4-MHz resonator

with integrated capacitors

is used to control the clock

frequency of the processor.

The reset input of IC1 is

connected to the positive

supply line via resistor R7.

The ON button (S4) gener-

ates a processor reset. LED

D6 also receives its nega-

tive supply voltage via S4.

Buttons S1 through S3 and

all the jumpers (see Table

1 ) are connected to Port B,

which provides internal

pull-up resistors. The indi-

cator scale LEDs are driven

via RA1 through RA4. Red

low-current LEDs are used

to reduce the current to

5/2000

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