This applet shows a seven segment BCD decoder made with TTL-7449 circuit. Converts a 4-bit binary encoded decimal value, ie the numbers 0 to 9 encoded as binary patterns 0000 to 1001, into the code required to drive a seven-segment display. The additional 'ndark' input allows you to disable all outputs.
For input values between 10 and 15, the 7449 type circuit generates seemingly "random" output values. Obviously, a simple implementation of circuits was more important for designers than to show useful output patterns (like the letters 'A' to 'F'); You can compare these output values with the values generated by the seven-segment decoder demonstrated in the previous applet.