Progressing toward the goal

A project log for Multiplexed 7-segment display


pavelPavel 06/29/2018 at 11:080 Comments

Since last log entry I had made two more boards, transcoder board and clock/drive/amp board.

Here is transcoder:

It includes 4-to-16 decoder circuit coupled with diode matrix (maybe better to call it ROM?). Its inputs are 4-bit binary numbers, its outputs are 7 bits for lighting 7-segment digits.

Component statistics:

2n2222a transistors:  20

1n4148 diodes:            102

red LEDs:                     20

10k resistors:                27

20k resistors:               20

47k resistors:               20

Total parts:                   209

also wires and 7*9cm perfboard.

Other plate:

This plate has four different circuits: one is just 7 driving sub-circuits meant to provide/deny sink for appropriate display segments; another is clock based on ~7 kHz multivibrator; third is two clocked data flip-flops connected as 2-bit counter; and last is regulated power supply based on 7805 IC (I like to think that it is not considered cheating to use power regulator IC in otherwise totally discrete component circuit) . The counter then feeds 2-to-4 decoder on display plate which chooses appropriate digit on display and appropriate nibble from 16-bit input word. 

Component statistics:

2n2222a transistors:          28

1n4148 diodes:                    28

red LEDs:                            19

100R resistors:                    7

1k resistors:                         11

10k resistors:                       21

20k resistors:                      12

47k resistors:                       19

10nF capacitors:                  2

100nF capacitors:                1

0.47uF capacitors:               1

7805 voltage regulator IC:  1

5.5 mm socket connector:  1

total parts:                            151

Also, of course, 7*9 cm perfboard and wires.

The last part to make is 16-to-4 multiplexer, which should take in 16-bit data word, 2-bit "address" and spew out 4-bit part of data word fed into it. I decided to make multiplexer from tri-state buffers, as it seem more straightforward, and this choice also holds down component count.