Hello,

I have built this circuit in order to make a string of LED Christmas lights. The lights are blinking nicely, but I would like to have 2 operating modes: flashing and lights on (not flashing).
Is it possible to do it with this design?

 

hi 83,
It is not possible with that circuit to light all the LED's at the same time.
E

 

You could try to reduce the 1uf capacitor to 0.1uf or less, when the flashing frequency quick enough and to then it will looks like all LEDs are lighing, but the LEDs brightness also will be a little darker than the lower frequency flashing.

 

Oh, that s bad news. Not even 3 of the outputs? I actually use only 3 of them.

 

hi,
Which three outputs.?
E

 

Oh, that s bad news. Not even 3 of the outputs? I actually use only 3 of them.

No 3 segments are always on.

What is the clock frequency? If it's fast enough, you might be able to use some that are mostly on (like a, b, and c).

 

Maybe you could switch to a CD4033B, which has a lamp test pin.

 

Thank you for all the answers.
I have pulled out the capacitor and all the leds are on. But i don t know if they will turn off after a while. I will have to observe

 

I think i will try a CD4033Bsince it has the same pinout. The lamp test pin is a very good idea. In the datasheet it says it has to be connected to high-level voltage. what does that mean? Connecting it to the Vss 9v will be enough?

 

I have pulled out the capacitor and all the leds are on. But i don t know if they will turn off after a while. I will have to observe

Shouldn't take more than 10 clock cycles to decide.

You haven't stated what your objective is, but you could use 3 OR gates to force 3 outputs to be high.

 

The datasheets of Texas Instruments for CD4xxx ICs have more detail (graphs) than other makes. TI says that if the supply is 9V and the loads are 1.8V red LEDs then typical ICs will have overloaded outputs and poor reliability. If 3.3V blue or white LEDs are used then there is no overloading. Two red LEDs in series can also avoid overloading.

 

The datasheets of Texas Instruments for CD4xxx ICs have more detail (graphs) than other makes. TI says that if the supply is 9V and the loads are 1.8V red LEDs then typical ICs will have overloaded outputs and poor reliability. If 3.3V blue or white LEDs are used then there is no overloading. Two red LEDs in series can also avoid overloading.

Actually i am going to use 3 transistors as a switch for each of the 3 outputs. I am going to use 10 leds in paralell for each of the output. I don`t know now exactly which of the pins will be used. First, I have to select them visually, by the output pattern (flicker or flash).

I will order CD4033 to check if the test output is the answer to my question (keep the ligts on).

 

hi dan,
A CD4000 device output pin will not drive 10 LEDs in parallel.
Using a transistor is required as you state
E

A point to note a NPN transistor will invert the signal sense.

 

I think i will try a CD4033Bsince it has the same pinout. The lamp test pin is a very good idea. In the datasheet it says it has to be connected to high-level voltage. what does that mean? Connecting it to the Vss 9v will be enough?

Connecting the Lamp Test pin to the +9 V rail will be fine. But -

Correction - in CMOS logic circuits, the positive supply rail is Vdd, not Vss. Vss is the GND pin.

ak

 

Hello,

I have built this circuit in order to make a string of LED Christmas lights. The lights are blinking nicely, but I would like to have 2 operating modes: flashing and lights on (not flashing).
Is it possible to do it with this design?

View attachment 231363

What do you mean "they blink nicely"?
The 4026 and 4033 is a 7-segment display driver. It won't work properly for christmas lights,
unless all the christmas lights are 7-segment displays.
Instead, do you want all the lights to either flash or blink? Or light up sequencially?

 

This video explains better than me about the blinking. I am going to use only three outputs to create 3 branches of 5 LEDs each (in parallel). The other outputs will be left unconnected. I haven t decided yet if i will use 11, 12 and 13 as in the schematic.

 

Leds in parallel do not look the same since their voltages do not match causing one or more to be brighter than the dim ones.
Your schematic with no supply voltage might be powered by a 9V smoke detector battery. The resistor feeding the parallel LEDs wastes 9V - 2V= 7V for red LEDs and wastes 9V - 3V= 6V for some other colors. Then the small battery life is very short.

If two LEDs are in series then the wasted battery power is halved. Each two LEDs in series needs a series current-limiting resistor.

ALL electronic circuits especially when powered from a battery need a supply bypass capacitor from the + voltage to the 0V. Use 100uF to 470uF.