Buying a gift for someone special or a
loved one can sometimes be difficult or expensive. The
flashing heart is the answer. It is easy to build and
even the inexperienced hobbyist should be able to build
it. The estimated cost for the circuit is $25 if all the
parts are purchased new. With The Flashing Heart, you
can get your message across in bright lights.
The Circuit Diagram is shown in Figure
1. It consists of a 4047 low-power monostable/astable
multivibrator, IC1, used in the astable mode to provide
the timing pulses to control the flash rate of the LEDs.
To accomplish the astable mode, pins 4, 5, 6, and 14 are
connected to +12VDC and pins 7, 8, 9, and 12 are
connected to ground. Pins 1 and 3 are connected to C2
and pins 2 and 3 are connected to potentiometer R9. A
fixed value resistor can be used in place of the
potentiometer R9, if the flash rate does not need to be
adjusted. These three pins make up the R-C timing
circuit. The output pulses from the 4047 are taken from
pins 10, 11, and 13. Pin 10 is the Q output and pin 11
is the Q-not output. These two pins are onnected to R6
and R7 respectively.
Click On
Images To Enlarge
The collectors of Q2 and Q3 are
connected to R4 and R5 respectively, which are connected
to the cathodes of the Yellow LEDs. Pin 13 is the
oscillator output and is connected to R8, which is
connected to the base of Q1. The collector of Q1 is
connected to R3, which is connected to the cathodes of
the Red LED's. The emitters of the three transistors are
connected to ground. The Green LEDs are connected to R1
and R2, which are connected to +12VDC. Resistors R1-R8
are current limiting resistors and the correct wattage
for these resistors should be used to prevent excessive
heat. The resistive values may be changed to vary the
brightness of the LEDs. The circuit is powered by PS1, a
wall transformer, which is connected to a filter
capacitor C1. It must be between 10 to 15 VDC and at
least 500mA.
Probably the most difficult part of this
project is making the printed circuit board, Figure 2.
The board used in the prototype took several hours to
make using dry transfers. Using a different technique,
such as photo resist, may be faster for the experienced
hobbyist. Once the board is etched and drilled, the
jumper wires should be placed on the board and soldered,
as shown on Figure 3. Next the 84 Yellow LEDs should be
placed around the border of the board, followed by the
42 Red LEDs that make up the heart and then the 16 Green
LEDs that make up the letters I and U. Resistors R1-R9
and capacitors C1and C2 should be placed on the board
next and then the power supply, PS1. Sockets were used
in the prototype for the I.C. and transistors. A socket
for the I.C. is required, but the sockets for the
transistors are not. Special care should be taken when
handling the CMOS I.C., as a static discharge will
destroy it. When you are finished soldering, check the
board over for mistakes. If everything looks okay, apply
power.
Click On
Images To Enlarge
Once power has been applied to the
circuit, the Red LEDs should all be flashing on and off
together. The Yellow LEDs should be flashing on and off,
but only every other Yellow LED should be on at one
time. The Green LEDs will stay on at all times. The
flash rate can be adjusted by turning R9. Connections
for a fixed value resistor for R9 are provided on the
board layout if preferred.To dress up the project, a
favorite photograph can be placed in the heart, and a
frame can be made to fit the circuit board.
Parts
List |
|
|
|
Resistors |
R1, R2 |
- |
470 ohm,
1/2-watt |
R3-R5 |
- |
100 ohm, 3-watt |
R6-R8 |
- |
1000 ohm,
1.4-watt |
R9 |
- |
5000 ohm
potentiometer |
|
|
|
Capacitors |
C1, C2 |
- |
100uF, 16 volts,
electrolytic radial |
|
|
|
Semiconductors |
IC1 |
- |
4047, low power
monostable/astable multivibrator |
Q1-Q3 |
- |
2n3643 NPN
transistor or equivalent |
|
|
|
Diodes |
|
|
LED1-LED84 |
- |
yellow
light-emitting diode |
LED85-LED126 |
- |
red
light-emitting diode |
LED127-LED142 |
- |
green
light-emitting diode |
|
|
|
Other
components |
PS1 |
- |
12VDC @ 500mA
wall transformer |
|
|
|
Miscellaneous: Jumper wire, solder,
printed circuit board, |
drill and
bits,14 pin I.C. socket, and a frame or
case. |
|