Hi Hans,
Instead of three 555 oscillators you could use 3 inverters from a 74C14 Cmos Schmitt-trigger hex inverter IC.

The output transistors of the CD4017 will overheat without current-limiting resistors (or just a common one) with your very high 12V supply. A 9V supply is safer and the LEDs will be almost as bright.

For 25mA output I would use 74HC4017 ICs with a common current-limiting resistor and a 6V supply. They can be clocked with a 74C14 bunch of oscillators.

__________________
Uncle $crooge

 

Would it be possible to connect caps across some of the led's so they dim away rather than swith off quickly? If so, what values would be good? 100uF?

 

Hi Hans,

It doesn't matter how much your simulator costs if your concept is
wrong. When the counters are counting the leds will be charlieplexed
and they will still light, not as bright but they will light.
I think you gonna have to make a (few) minor modification(s) to your
design.

on1aag.

Attached Images

	Twinkling leds 1.PNG (34.3 KB, 21 views)
	Twinkling graphs 1.PNG (14.7 KB, 23 views)

 

If you add a capacitor across each LED then they will turn off fairly quickly because the output of a CD4017 goes low when the LED is turned off.

If you add a diode in seies with each LED and a capacitor across each LED then the capacitor will discharge fairly slowly into the LED without being discharged quickly when the output of the CD4017 goes low.

Try different capacitors.

__________________
Uncle $crooge

 

Hi Trevors,

the caps across the LEDs won't do much. Better use low power MosFets and keep the gate voltage high long enough so the LEDs will extinguish slower. However they won't twinkle anymore.

Hans

 

Hi on1aag,

the longer I look on the schematic the lesss charlieplexing I find. The LEDs will twinkle at full brightness depending on the current. As audioguru already pointed out either the LEDs or the counter will give up sooner or later with a supply voltage of 12V and no current limiting resistors.

Especially for you here is the difference between multiplexing and charlieplexing. Neither one applies to my suggested circuit.

For more info about charlieplexing visit maxim-ic.com.

Best regards

Hans

 

Oops,

just selected the wrong power source. Should have been 9V though.

I'm not too good at math. Please tell me the difference in making the astables with 3 out of 6 inverters per circuit and using dual timers for the same purpose. My vague calculation results in three ICs in both cases.

You'll also have half of an IC leftover for general use.

Greetings

Hans

 

Hi hans,
You can make an astable from a single Schmitt-trigger inverter (6 in a package) or from two ordinary inverters.

Attached Images

Cmos Oscillators.PNG (11.6 KB, 11 views)

__________________
Uncle $crooge

 

I've made bad experience at lower frequencies. (below 1KHz). For myself I think the choice of a timer circuit is best.

 

That's probably because you used TTL, not CMOS and used to small resistor and too large capacitor values.

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Absolutely correct! 40 years ago there were no CMOS ICs. I haven't tried again.

 

I started using Cmos about 30 years ago. Then I stopped using 74LSxx TTL about 25 years ago and I have used Cmos ever since.

__________________
Uncle $crooge

 

Exactly right the first point, not right concerning Rs and Cs. 45 years ago there were no CMOS ICs. I didn't even bother trying later.

 

Big change!

after all the good advises I've tried to make the astables using a CD106 inverting Schmitt-Trigger.

The clocking works well. This way 50 LEDs can be lit with 6 ICs, one for a clock signal oscillator and five clock inhibit oscillators, five ICs for the counters.

Using junk resistors and capacitors they might all be of the same value causing different frequencies which are a MUST for that circuit.

A tolerance of 40% would make the circuit perfect.

Otherwise modify the R and C values slightly for different clock inhibit frequencies.

Hi audioguru, did you have your divorce yet?

 

Divorce?
No, I am happily married.
Oh, I divorced power-hungry TTL about 25 years ago.

__________________
Uncle $crooge