06-10-2012, 11:58 AM
RUNNING MESSAGE DISPLAY
[attachment=35492]
LEDs are advantageous due to their smaller size
and low current consumption. Here is a running
message display circuit wherein the letters
formed by LED arrangement light up
progressively. Once all the letters of the
message have been lit up, the circuit gets reset.
This message display circuit is built around
readily available, low cost components. It is easy
to fabricate and makes use of 3mm red LEDs. A
total of 70 LEDs have been used to display the
message “WELCOME”.
The arrangement of LED1 through LED15 is
used to display 'W' as shown in Fig. 1. The
anodes of LED1 through LED15 are connected
to point A and the cathodes of these LEDs are
connected to point B. Similarly, Other letters can
also be built.
Two ICs, the timer 555 (IC2) and decade counter
CD4017 (IC3), are used to build the display
circuit. One of the IC CD4017's features is its
provision of ten fully decoded outputs, making
the IC ideal for use in a whole range of
sequencing operations. In the circuit only one of
the outputs remains high and the output
advances by one count every second
(depending on the time period of astable
multivibrator IC2). The timer IC NE555 (IC2) is
wired as a 1Hz astable multivibrator that clocks
the IC3 for sequencing operations.
When Q1 output of IC3 goes high, transistor T1
conducts and the current flows through LED1
through LED15 via resistor R9. Now the letter 'W'
built around LED1 through LED15 is displayed
on the LED arrangement board.
Next, when Q2 output of IC3 goes high,
transistor T2 conducts and letter 'E' lights up.
The preceding letter 'W' also remains lighted
because of forward biasing of transistor T1 via
diode D5. In a similar fashion,
[attachment=35492]
LEDs are advantageous due to their smaller size
and low current consumption. Here is a running
message display circuit wherein the letters
formed by LED arrangement light up
progressively. Once all the letters of the
message have been lit up, the circuit gets reset.
This message display circuit is built around
readily available, low cost components. It is easy
to fabricate and makes use of 3mm red LEDs. A
total of 70 LEDs have been used to display the
message “WELCOME”.
The arrangement of LED1 through LED15 is
used to display 'W' as shown in Fig. 1. The
anodes of LED1 through LED15 are connected
to point A and the cathodes of these LEDs are
connected to point B. Similarly, Other letters can
also be built.
Two ICs, the timer 555 (IC2) and decade counter
CD4017 (IC3), are used to build the display
circuit. One of the IC CD4017's features is its
provision of ten fully decoded outputs, making
the IC ideal for use in a whole range of
sequencing operations. In the circuit only one of
the outputs remains high and the output
advances by one count every second
(depending on the time period of astable
multivibrator IC2). The timer IC NE555 (IC2) is
wired as a 1Hz astable multivibrator that clocks
the IC3 for sequencing operations.
When Q1 output of IC3 goes high, transistor T1
conducts and the current flows through LED1
through LED15 via resistor R9. Now the letter 'W'
built around LED1 through LED15 is displayed
on the LED arrangement board.
Next, when Q2 output of IC3 goes high,
transistor T2 conducts and letter 'E' lights up.
The preceding letter 'W' also remains lighted
because of forward biasing of transistor T1 via
diode D5. In a similar fashion,