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# using a 7448 decoder and 7 segment cathode

Discussion in 'The Projects Forum' started by cjjg, Oct 5, 2008.

1. ### cjjg Thread Starter New Member

Oct 5, 2008
2
0
guyz, i rily had a hard tym on this... can u please help me...
i need to construct a circuit using 7448 decoder and a 7 segment cathode...
the situation goes like this.....

\=> if 0,7,4,2,5 is switched on, the 7 segment cathode will display those numbers... otherwise it's off (it won't display anything) but.....
if numbers 10,11,12 is switched on, it will display 0(zero) and
if numbers 13,14,15 is on, it will display 8(eight).....

i badly need ur help!

2. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
Sounds like you have your ABCD inputs scrambled in with the RBI (ripple blanking input)
A is the LSB of the digit.
D is the MSB of the digit.
Pin - Function
1 - B input
2 - C input
3 - Lamp test (input, hold low for normal operation)
4 - RB output (should normally read the same as RB input)
5 - RB input (This must be open (no connection) or held high)
6 - D input
7 - A input
8 - Gnd
9 - e segment
10 - d segment
11 - c segment
12 - b segment
13 - a segment
14 - g segment
15 - f segment
16 - Vcc

3. ### mik3 Senior Member

Feb 4, 2008
4,846
70
Wire the 7848 with the display as you would if you wanted to display all the numbers. Finally, use combinations with AND gates to control the LT pin (lamp test) and zero blanking control (RBI) to turn on all the leds or turn them all off at the desired numbers. The AND gates will take signal from the output of the counter or whatever drives the four inputs of the 7848. Read the datasheet for the 7848 pin configuration.

4. ### cjjg Thread Starter New Member

Oct 5, 2008
2
0
thanks a lot!