# 3 light chaser circuit

Discussion in 'The Projects Forum' started by raisintoe, Oct 26, 2015.

1. ### raisintoe Thread Starter Member

Mar 24, 2012
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I would like to make a circuit, (without using any ICs), that chases 3 lights, (1 channel on at a time). I have tried expanding a 2-channel astable multivibrator circuit to 3 channels, but 2 lights are on at once instead of just one.

So, how should I go about making such a 3-channel light chaser? It might be more complex than I think.

2. ### TheButtonThief Active Member

Feb 26, 2011
219
38
make a shift register using just transistors. There'd be a lot of them but think about it, an IC is just a heap of tiny resistors so if you want to build a circuit that would be easily done with an IC but you don't want to use the IC, just build the equivalent circuit with transistors.

3. ### DickCappels Moderator

Aug 21, 2008
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Is this what you were trying to do?

absf and TheButtonThief like this.
4. ### raisintoe Thread Starter Member

Mar 24, 2012
46
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Oh, yeah! That works great. I'll be lighting some 6v incandescent lights though, (2 with 18 ohm loads, and 1 with a 15 ohm load), so I'd have to use a higher voltage, Maybe 12v and divide the voltage with corresponding 18 ohm and 15 ohm resistors instead of the 1K resistors. I do have some 1A rated transistors that would work for this. I wonder if there is a way for me to pull less current through the transistor, 600mA is a lot to pull just to turn a light off.

5. ### raisintoe Thread Starter Member

Mar 24, 2012
46
0
Oh gee, then I would have to have about an 8 Watt resistor!

6. ### raisintoe Thread Starter Member

Mar 24, 2012
46
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Hmmm, my LTSpice simulator can not run this, and I don't have any 1A pnp transistors on hand, but I wonder if this would work. I disconnected the load from across the npn transistor, then I use a pnp transistor to operate the load. I wish I was more familiar with using pnp transistors.

What do you think?

7. ### raisintoe Thread Starter Member

Mar 24, 2012
46
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Oh, no that won't work, I was thinking TTL logic

8. ### raisintoe Thread Starter Member

Mar 24, 2012
46
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I just need to ditch the 100K resistor, don't I? Then it should do 1 light at a time. I'll use a diode to drain the capacitor to ground also.

9. ### blocco a spirale AAC Fanatic!

Jun 18, 2008
1,463
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If you google "3 light chaser circuit" (that's weird, it's identical to the title of this thread) there are lots of examples of this type of circuit, some even use incandescent lamps:
http://www.bowdenshobbycircuits.info/page5.htm

10. ### raisintoe Thread Starter Member

Mar 24, 2012
46
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I did find this circuit the other day, and I built it, but it didn't work very well. I used 25 ohm resistors for the load resistance.

11. ### Dodgydave AAC Fanatic!

Jun 22, 2012
5,167
777
If you use PNP just make sure the Emitters go to the positive supply just as NPN go to negative supply.

12. ### raisintoe Thread Starter Member

Mar 24, 2012
46
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well, I tried my simulator with those values. But
OK thanks, I always thought that the emitter went to the negative supply.

13. ### raisintoe Thread Starter Member

Mar 24, 2012
46
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Well, I tried my simulator with those values in the Xmas light schematic, but I built my circuit using a 470 ohm load with LEDs, and a 9v battery; all other values are the same. The effect is confusing; sometimes I can trigger a very slow chase by charging one of the capacitors before running it. But I always read about a 140ns wave period on my oscilloscope between the capacitor and the 100 ohm resistor. I tried changing the capacitors from 220uF to 22uF, and nothing changed.

14. ### Dodgydave AAC Fanatic!

Jun 22, 2012
5,167
777
Why dont you use a 555 timer clock to feed a Cd4017 decade counter, set to 3 instead of all this hassle with transistors??

15. ### raisintoe Thread Starter Member

Mar 24, 2012
46
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Hmm, it looks like the 140ns wave is coming from the diodes.

Well, Dodgydave, it looks like I will be using a 555 timer or something similar, I just thought this circuit could be simply done with a few transistors and capacitors.

16. ### raisintoe Thread Starter Member

Mar 24, 2012
46
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The real issue is that I need to drive 6V incondecent lighting. this requires a much higher load than any LED, so I have to drive this load through some external circuitry. I would have to trigger an external transistor through a buffer for each channel. This would work, except that I am trying to fit all of this in a very small space of 1.875 X 0.9375 inches.

Maybe surface mounting chips will be small enough.

17. ### Dodgydave AAC Fanatic!

Jun 22, 2012
5,167
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Surface mount best,with mosfets for lamp driving.

18. ### raisintoe Thread Starter Member

Mar 24, 2012
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Ha ha ha! So the noob strikes again! All I had to do was use the astable multivibrator model as a reference to trigger my load: