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I've realized the circuit as scheme attached.
When the output pin is high the BC547 drive led properly.
When the output pin is down I've a constant bright light on led.
Why?
I've also put a 1N4148 in series to led but... nothing.
Any help?
Why not use an ULN2003 easier to use than a bunch of transistors.
re check to see if you have a pulse output. If you do then re check the output pins if they are working right?
If all is good then you have a transistor connected wrong or is bad.
to amitpj & MrDEB
Yes, I've got impulse out from CD4017. If a led is connected in every leads, I've got the right, unique flash when the pin goes up.
Only when I connect a BC547 (like the scheme show) to drive a HB led I've:
OUTPUT DOWN - feeble light on led
OUTPUT UP - high bright light on led
to MrDEB
Nice the ULN2003. I'll search in some electronic shop in city. Good idea.
I think we have another symptom here of using a breadboard:
1) Output of CD4017 goes low which makes the base current in the transistor zero.
2) With a base current of zero then the collector current of the transistor is also zero.
3) But the long wires on the breadboard are acting like antennas for all the radio and TV stations in town (and all the cell phones) and feebly lights the LEDs.
Try connecting a 3.3k resistor in parallel with each LED to fix it.
Ok audioguru, I'll try and YES, I'm using a breadboard.
Here a movie of the circuit.
First led is that one connected directly to CD4017.
The second is connected through the BC547.
The 555 in your circuit creates 400mA supply current spikes that cause the 9V from the battery to momentarily collapse each time the output changes.
Datasheets for the 555 say that supply bypass capacitors are required to prevent the collapse.
Try connecting a 100uF capacitor in parallel with the battery.
Maybe the feebly blinking LED is picking up radiation from the output of the 555 since it seems to blink at about 10 times the normal rate. Again it is caused by the long messy wiring of a breadboard.
Isn't the 555 on a different breadboard than the CD4017? Then the 400mA supply current spikes are causing a voltage drop in the wiring between the two which might cause the transistor to turn on each time the 555 changes.
If you use a Cmos 555 like an LMC555, TLC555 or ICM7555 then there will not be any supply current spikes.
No audioguru. Also with 3,3k in parallel i've a feebly light when output is DOWN.
And if the problem is from NE555? The output from pin 3 to pin 14 of CD4017 is not good?
If I've more time I'll realize a pcb.
Mikebits,
Didn't you see the video? The LED driven by the transistor faintly blinks about 10 times when it should be turned off. So the LED is driven at the same rate as the output of the 555 (I think) and is not continuously turned on like if something is connected wrong.
I've try to replace le hb led with another red standard and the feebly is not present (or I can't see it). Same result with another green standard.
But when I use hb white led with transparent lens (I've different type of them from 60mcd to 285mcd) the feebly is present between one and other flash.
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