Download Infra-Red Switch

5
Infra-Red Switch
1.
Single Channel Switch
Transmitter
+9v
4
R1
8
3
7
555
5
R2
6
1
2
C
-
The component values must be chosen to give a frequency of oscillation
to suit the receiver module to be used. In most cases this will be 40kHz
but you should verify this before starting construction. The resistance in
series with the diodes should be about 22Ω (its value is not critical).
To calculate the frequency of oscillation of a 555 oscillator, use the
following formula:
f =
1.44
(R1 + 2 R2 )C
For example, if we choose C = 1·5nF and R2 = 10k this gives R1 =
(about) 5k for a frequency of 40kHz. We should therefore use a 10k
variable resistor for R1. This will allow us to set the frequency to exactly
40kHz. For stability of frequency, a voltage regulator is recommended
(the vero diagram below includes a regulator).
1
Receiver
This circuit uses a ready-made I.R. receiver module. These modules are
very sensitive and this simplifies the construction. The modules need a
stable power supply so the 7805 voltage regulator is necessary. The opamp is a TL081.
+
7805
2
5 14
47k
3
1
4013
4k7
470n
7
100k
6
100k
I.R. receiver
module
to I.R.
receiver
module
4
+
-
in
gnd
out
10
1
1
to relay
5
e
b
c
20
1
1
5
10
15
25
10
1
1
5
1
25
20
15
10
2
5
1
2.
Two Channel Switch
Transmitter
The 555 oscillator connected to the diodes is set to oscillate at the
correct frequency for the I.R. receiver module to be used. The second
oscillator modulates the first oscillator at a frequency of a few hundred
Hertz. By varying the frequency of the modulation, we can change the
“channel”.
out
7805
gnd
4
8
3
4
10k
3
7
555
5
7
555
1k
6
1
8
5
2
6
1
2
1·5n
+
in
gnd
out
to diodes
1
5
1
1
1
5
10
15
20
-
25
1
5
1
1
25
20
15
3
10
5
1
in
Receiver
The 567 chips are needed to demodulate the signal sent by the
transmitter. The circuit below was originally designed to drive a small
d.c. motor (connected to points x and y). Activating one channel drives
the motor one way and the other channel drives it the opposite way.
However, the outputs of the 567 chips could be used to drive relays if
required.
+
8
4
3
567
7
5
6
2
y
x
1
I.R. receiver
module
+
10k
220n
8
4
3
567
7
5
6
2
1
100k
220n
10µ
1
1
in gnd out
1
c
b
e
e
b
c
e
b
c
1
c
© David Hoult 2001
4
b
e