simple 5 led flasher (like night rider)

[audioguru]

Hi Arun,
The 4017 outputs don't have enough output current to do what your circuit needs.

For example the 6th output must drive 5 LEDs plus the base of the reset transistor. The current from the 6th output is only a few mA so each LED will have less than 1mA each. The 1st LED will start fairly bright then it will get dimmer and dimmer as each output sequences.

 

[nura100]

Hello Audioguru,

Yes, i forgot to add a note about LEDS brightness,

i just wanted Fever to figure out the probable flaw in the circuit diagram, and then i would have suggested the use of transistors at the O/Ps of 4017

arun

 

[fever]

guru iam still waiting for ur reply abt the ckt i posted above.imean LM3914 with transistor circuit
is it ok.i have bunch of 3914's so i want to test it first.

 

[audioguru]

Hi Fever,
Your transistor circuit will cause all LEDs to be on when it is turned on, then they will suddenly all turn off after a delay.

Test the LM3914 in the LM3915 circuit I sketched. You might like the way the capacitor voltage rises quickly in the beginning then slows down as it gets more charged.

 

[nura100]

Hello Audioguru,

how about my revised circuit, does this solve the problem?

Fever, don't get scared by the number of Diodes, its a simple circuit and costs less than LM3914 IC

you also have learned about using RESET Pin of the timer.

best of luck

Modifications Welcomed!

arun

 

[audioguru]

Hi Arun,
With a brand new 9V battery your revised circuit doesn't have enough voltage for the first two LEDs when they are all on. Also, when the battery voltage quickly drops to 6V then most LEDs won't work. The LEDs will have changing brightness. The transistors should be common-emitter. R12 and Q7 are not needed.

Your circuit also has too many parts to light only 5 LEDs.

 

[Hero999]

Microcontroller maybe?

I really need to get round to building/buying a programmer.

 

[fever]

it may solve the problem.
but if a simple (3914 or 15) chip can solve the problem.why Micro?

 

[kchriste]

how about my revised circuit, does this solve the problem?

Sort of..... How about a little RTL logic?

 

[audioguru]

31 resistors, 6 transistors, a 4017 and a 555 just to replace an LM3915?

 

[kchriste]

31 resistors, 6 transistors, a 4017 and a 555 just to replace an LM3915?

It DOES seem silly unless the OP can't find a LM3915 or 14....
If I was to do it with logic ICs I would have chosen a shift register, grounded the serial input, puts the LEDs on the parallel outputs, and clocked with the 555 etc... That would eliminate the RTL logic, but it was a fun birdsnest to mod.