It's a little more complex than that as shown in my POLICE LIGHTS project.
You have to take into account the voltage across the gating diode and the minimum voltage on the output of the 555.
See my "50 555 PROJECTS" on Talking Electronics website, for the circuit.
the decimal counter needs to be connected for one gap between outputs. Otherwise the connected LED just lights for two clock pulses without interruption. Having one more output pin would solve the problem.
I didn't want to make it more complicated cascading two counters.
I guess neither circuit will flash a pair of LEDs three times alternating. With the values given in your circuit the LEDs flash ten times, while with mine they flash twice.
Colin- does your circuit actually synchonise to exactly 3 beats per light? I think a 4017 solution would be better.
Boncuk- sorry I didn't explain the mod to your circuit very well and I made a mistake.
1. First add 2 diodes so that the 4017 has 6 diodes to the 2 transistors.
This means each led will be on for a period of 3 ticks.
2. Now attach the 555 output through another 2 diodes to the base of each transistor.
Now when the 555 output is low it turns off the transistors. So the leds flash in time to the output of the 555. The 4017 sequences 3 flashes of LEDa and 3 flashes of LEDb.
Colin made a good point about the diodes might not fully turn off the transistors when the 555 output is low. You could get around this in heaps of ways by using FETs, or darlingtons, or schottky diodes, or 2 resistors from base to ground. Also a CMOS 555 might do it too with no other mods.
Here is my circuit to stop all the jumping around with descriptions that don't make any sense.
The point to note here is the fact that you described a circuit without actually building it. I learnt not to try that trick, 40 years ago when I suggested a frequency-to-voltage converter without having actually built it.
No 555 is going to turn off a transistor via a gating diode.
Both of my circuits flash each LED 3 times. You can adjust the dual 555 circuit to produce the exact flash-rate, and effect, you desire.
Here is my circuit to stop all the jumping around with descriptions that don't make any sense.
The point to note here is the fact that you described a circuit without actually building it. I learnt not to try that trick, 40 years ago when I suggested a frequency-to-voltage converter without having actually built it.
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No 555 is going to turn off a transistor via a gating diode.
Both of my circuits flash each LED 3 times. You can adjust the dual 555 circuit to produce the exact flash-rate, and effect, you desire.
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Now I think you have been sloppy. I proposed a number of working solutions, ie FETs, darlingtons, schottky diodes, with or without CMOS 555 these are all workable ideas and I was deliberately trying to avoid the messy 4 resistor addition that you used (which was my first knee jerk reaction before I thought of better ways).
After a bit of thought, the lowest possible parts count is probably using 2 darlingtons, driven by 6 resistors from 4017 (good idea Colin!), and 2 diodes to turn the darlingtons off.
Boncuk- the last circuit you drew may require schottky diodes, it needs to pull the bases of the transistors below 0.6v to properly turn them off. Also a CMOS 555 might be needed, they are the only type most people buy these days anyway.
In my cirucit, you will see I have a voltage divider on the base of each transistor to turn it off.
Without the voltage divider, the transistor will not turn off.
Is that enough proof?
Why don't you actually build the circuit and prove it will work, before putting it on the web?