# 3 light chaser circuit

#### raisintoe

Joined Mar 24, 2012
46
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.

#### TheButtonThief

Joined Feb 26, 2011
237
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.

#### raisintoe

Joined Mar 24, 2012
46
Is this what you were trying to do?

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.

#### raisintoe

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

#### raisintoe

Joined Mar 24, 2012
46
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?

#### raisintoe

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

#### raisintoe

Joined Mar 24, 2012
46
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.

#### blocco a spirale

Joined Jun 18, 2008
1,546
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

#### raisintoe

Joined Mar 24, 2012
46
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
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.

#### Dodgydave

Joined Jun 22, 2012
11,152
If you use PNP just make sure the Emitters go to the positive supply just as NPN go to negative supply.

#### raisintoe

Joined Mar 24, 2012
46
well, I tried my simulator with those values. But
If you use PNP just make sure the Emitters go to the positive supply just as NPN go to negative supply.
OK thanks, I always thought that the emitter went to the negative supply.

#### raisintoe

Joined Mar 24, 2012
46
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.

#### Dodgydave

Joined Jun 22, 2012
11,152
Why dont you use a 555 timer clock to feed a Cd4017 decade counter, set to 3 instead of all this hassle with transistors??

#### raisintoe

Joined Mar 24, 2012
46
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.

#### raisintoe

Joined Mar 24, 2012
46
Why dont you use a 555 timer clock to feed a Cd4017 decade counter, set to 3 instead of all this hassle with transistors??
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.

#### Dodgydave

Joined Jun 22, 2012
11,152
Surface mount best,with mosfets for lamp driving.