Back and Forth Flasher
by Forrest Mims III


Demultiplexer
1-to-16 Demultiplexer - Selected output is low when Data IN is low.
If Data IN is high, then selected output is high also.
Each 4-bit address drives one output low. All others stay high.
Enable inputs (E1 & E2) must be low.
If one or both are high, all inputs go low.




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Parts List:

U1 = SN74154 (demultiplexer) (may be difficult to get)
U2 = LM555 (timer)
U3 = SN74LS00
U4 = SN74LS190
P1 = 100K
R1 = 1K
R2 = 470-Ohm
C1 = 0.33uF(tantalum)
16 LED's, high brightnes or ultra-bright
Table 1 - Connection Scheme
Pos
IC Pin # La # Color Wir Wire
1. 74154 Pin 1 Led 1 Green Or Orange
2. 74154 Pin 2 Led 2 Yellow Whi White
3. 74154 Pin 3 Led 3 Yellow Blu Blue
4. 74154 Pin 4 Led 4 Red Blk Black
5. 74154 Pin 5 Led 5 Red Rw Red/White
6. 74154 Pin 6 Led 6 Red Gw Green/White
7. 74154 Pin 7 Led 7 Red Bw Blue/White
8. 74154 Pin 8 Led 8 Red Bw Black/White
9. 74154 Pin 9 Led 9 Red Or Orange/Red
10. 74154 Pin 10 Led 10 Red Br Blue/Red
11. 74154 Pin 11 Led 11 Red Bkr Black/Red
12. 74154 Pin 13 Led 12 Red Rb Red/Black
13. 74154 Pin 14 Led 13 Red Bb Blue/Black
14. 74154 Pin 15 Led 14 Yellow Gb Green/Black
15. 74154 Pin 16 Led 15 Yellow Pi Pinkk
16. 74154 Pin 17 Led 16 Green Pu Purple
17. Gnd 12/18/19 Common to everything Gnd everything Green
18. Vcc+ 24 and anodes 5.5V to 7.5V Re 5 - 7.5 V Red
19. n/a
20. n/a
21. n/a
22. n/a
23. n/a
24. n/a

A Couple of Final Notes:
Click here [LM555] for more information and data on the 555 timer/oscillator IC. Keep wires as short as possible since too long wires coming from the 74154 to the led's will give trouble getting them 'running' properly. The 74154 may be difficult to get these days and may be pricy.
I had this circuit installed in the nose of my R/C helicopter before I sold it and the circuit was working good.
This circuit is for those electronics persons with experience only. In either case, it is definately a good learning experience. Have fun!

Copyright and Credits:
This circuit diagram is copyright Forrest Mims III, and is published in his publication: "Engineer's Notebook", listed page 61.
Posted with permission.
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Copyright 1993 © Tony van Roon