Building is built in O Scale (1/48) and has 40 rooms that are lighted independently (masked out from each other with walls) Rooms are lighted with White LEDs. The rooms will light one at a time (but in different areas of the building to make it appear random)until all 40 rooms are lighted. Than they will turn off in reverse order until all off and than the cycle repeats. A 555 is used as the clock with about a 5 second pulse rate so the complete cycle will be a little over 3 minutes. This is a large model building for my train club that has open houses for the public. Purpose of circuit is to make the building have a different look every time it catches your eye. The LEDs will be powered from 12 volts, the logic will be accomplished by the 555 as mentioned, along with recently purchased TLC5916 8 Channel LED Sink Drivers (5 of them cascaded to get 40 channels, 1 per building room)

I have had some success on a dual chip (16 bit) circuit on a breadboard but know it is not right as it requires a zener diode to make it work and when I tried to expand the circuit out to 5 cascaded chips on a production wire wrapped board it failed miserably.

I am pretty sure Pin 2 (SD1) and Pin 3 (CLK) need to be tied together on all five chips to Pin 3 of the 555 Timer. The question is than, what do I do with Pins 4 (LE(ED1), Pin 13 OE(ED2), PIN 14 (SDO) and I presume Pin 12 (OUT7) of the 5th Chip needs to get tied somewhere else besides the final 40th LED it drives to reset the circuit, but where and how? I am at a loss, have spent many hours and tried every combination of connections possible. Any ideas or schematics would be greatly appreciated!

TY in advance

  • \$\begingroup\$ Isn't LED light too synthetic-looking in a model railroad, compared to miniature incadescent bulbs? \$\endgroup\$ – venny Sep 3 '14 at 21:12
  • \$\begingroup\$ By "turn off in reverse order" do you mean that the last light to turn on should be the first one to turn off? Or it is OK for the lights to go out in the same order as they went on (ie. first one on is first one off)? \$\endgroup\$ – Bruce Abbott Sep 3 '14 at 21:27
  • \$\begingroup\$ I'm thinking like an audio VU meter that you see on EQ's. If it were 40 LED's tall, it would light from bottom to top, leaving them all on, then drop (turn off) from top to bottom. 40 outputs worth of shift registers in a FILO (First In Last Out) configuration and the 555 as the clock sounds like it could work but there may be better answers out there, but hopefully this will give you some google material and get your idea-maker working. \$\endgroup\$ – Enemy Of the State Machine Sep 4 '14 at 0:58
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    \$\begingroup\$ Matter of opinion, there are "Warm" and "Cool" White LEDs that look like incandescent and florescent lights respectively, LEDs last longer, use less power, cost less, run cool, and are more easily adaptable to model railroading. \$\endgroup\$ – Wdasilva76 Sep 4 '14 at 3:29
  • \$\begingroup\$ No, 1st on is 1st off, otherwise the 40th room wood in essence just be a 5 second blink. \$\endgroup\$ – Wdasilva76 Sep 4 '14 at 3:34

The circuit below should do what you want.

It works by inverting the output of the 40 bit shift register chain, a bit at a time, and then feeding it back to the input so that the data in the register recirculates forever, inverted each time it goes through.

One caveat is that since you're not using an MCU and the chip has no RESET, if the data in the register comes up as something other than all zeros or all ones on power-up, the pattern stored in the register, and its complement, will circulate forever. Not necessarily a Bad Thing, but if that happens the lamps will never be all on or all off at once. enter image description here

  • \$\begingroup\$ TY Mr. Fields, the addition of the Q made the difference! The circuit works perfect now! Can't thank you guys enough for your Knowledge and time!!!!!!!!!!!!!!!!!!!!!! \$\endgroup\$ – Wdasilva76 Sep 5 '14 at 7:40

Pin 3 (CLK) of each driver should be tied to pin 3 of the 555. Pin 4 (LE) should be tied to Vdd.

Pin 2 (SDI) of each driver is connected to pin 14 (SDO) of the previous driver. However between the first and last chip the signal can be inverted to create a 'first on, first off' sequence. If you assign the LEDs to random rooms then this may give a more natural effect than 'last on, first off', which is just as well because the other way is much harder to implement!

Note:- This will only work properly if the drivers power up with all outputs off. If not then you will need a more complex circuit.

To provide a stable +5V supply for everything that needs it I would use a voltage regulator rather than a Zener diode.

Here's an example circuit. For clarity I have only drawn 3 driver chips. To use 5 drivers, just duplicate the middle section.

LED sequencer


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