LED blink and off

[spec07]

Hi guys,

I have a current project which requires me to light up 7 LEDs in series using a on/off switch, blink for 5 secs (timing can be more) at the same time and turn off.

Is there any available circuit similar to this application? It has to be mobile as well, I'm thinking of powering the circuit with a typical 9V battery. Not sure if it is enough.

Any idea?

 

[AnalogKid]

By "in series", do you mean one after another, or all at once connected in series? Connected in series, 7 standard LEDs will require over 14 V at 20 mA, so you could do this with two 9V batteries connected in series.

Apply power to turn on, blink for 5 seconds, automatically shut off, correct? If so, this can be done with a CD4020 or 4024 divider, a driver transistor, and a CD4093 gate package for the oscillator and reset flipflop.

ak

 

[dougy83]

By "in series", do you mean "in sequence"?

If it's as AnalogKid stated, where the LEDs are all turned on together, then just a 4093 and transistor driver can give the flash and auto turn off. I suspect that's not what you're after; if you want a sequence of a single LED on, two LEDs on, ... all LEDs on, then all flash together, then all off, it can be done using an oscillator feeding a shift register (for the sequential lighting), followed by another oscillator to flash the LEDs, and a timer to turn everything off.

 

[spec07]

By "in series", do you mean "in sequence"?

If it's as AnalogKid stated, where the LEDs are all turned on together, then just a 4093 and transistor driver can give the flash and auto turn off. I suspect that's not what you're after; if you want a sequence of a single LED on, two LEDs on, ... all LEDs on, then all flash together, then all off, it can be done using an oscillator feeding a shift register (for the sequential lighting), followed by another oscillator to flash the LEDs, and a timer to turn everything off.

What I need is for the 7 LEDs to be turned on together, blink for 5sec and turn off together. In this case, what should I do? Is there any available circuit which I can follow? I am really bad at designing circuits and hope to get a full circuit solution if possible. This project is too tough for a 14 like me.

Please help and thank you for your reply!

 

[spec07]

By "in series", do you mean one after another, or all at once connected in series? Connected in series, 7 standard LEDs will require over 14 V at 20 mA, so you could do this with two 9V batteries connected in series.

Apply power to turn on, blink for 5 seconds, automatically shut off, correct? If so, this can be done with a CD4020 or 4024 divider, a driver transistor, and a CD4093 gate package for the oscillator and reset flipflop.

ak

Appreciate your reply! This sounds tough to understand. Any available circuits for me to turn on 7 LEDs, blink for 5 sec and turn off?

 

[dougy83]

You can use two 555 timers, like shown in the following schematic. I didn't mark the resistor values in series with the LEDs, but they should be (from left-to-right) 180R, 180R and 420R.

 

[AnalogKid]

This also can be done with a single NAND gate, or a combination of gates. Here are two schematics to show this. The functions are the same as the two-555 approach: an ON timer, enabling an oscillator, driving the LEDs.
Here is a calculator for the oscillator and the ON timer:
http://talkingelectronics.com/pay/BEC-2/Page49.html

ak

 

[Colin]

You can't drive 7 LEDs in series with 9v.
Do you want the circuit to take NO POWER after 5 seconds.

 

[Tony Stewart]

Hi guys,

I have a current project which requires me to light up 7 LEDs in series using a on/off switch, blink for 5 secs (timing can be more) at the same time and turn off.

Is there any available circuit similar to this application? It has to be mobile as well, I'm thinking of powering the circuit with a typical 9V battery. Not sure if it is enough.

Any idea?

It wont last longer than a day or 2 on a typ. Alkaline 9V

Can you use 8 instead of 7?
I use 10,000 mcd 30 deg @20 mA @2.0 to 2.1V Red or Yellow (630 nmD or 590 nmD) LEDs which would plenty bright on 3~5mA for most App. .... Blinding on 20mA at arms length.

For more constant brightness use 3S2P + 1S as suggested already but then 3 strings of current means 33% shorter battery life.

Timing is pretty easy. Search google "images" for "Schmitt Relaxation Oscillator" Using a big R to slowly charge a big C, the RC product gives the rise time of T seconds will be equal on and off. I suggest a good quality 1uF cap (low leakage uA spec) and R= 4.7M for approx 5 second On then 5 s off.

Ohm's Law is used to compute voltage drop between Vcc =battery and LED string . For 8V string and 9V battery, the LEDs will gradually dim as the battery drains to 8V.. Other methods using a string of 3LED of a red or yellow sum of 6V will allow the battery to drain fully but then consume 33% more current with 3 strings vs 2 , so , duration is not improved.

I could find a schematic but, learning to search Google Images for schematics helps train you.

Ok maybe you need more help... **broken link removed**

Running at 5mA per string x2 may get you a week runtime....

 

[Tony Stewart]

These use 2 Whites in series with a series R then cascaded in parallel to run from 6 to 14V with variable current.

https://www.instructables.com/id/LED-light-strip-Long-Board/?download=pdf

 

[Tony Stewart]

These use 2 Whites in series with a series R then cascaded in parallel to run from 6 to 14V with variable current.

https://www.instructables.com/id/LED-light-strip-Long-Board/?download=pdf

 

[Colin]

Here is the type of circuit you need:

LED FLASHES FOR 5 SECONDS AFTER BUTTON IS RELEASED
This circuits uses a FLASHING LED - not an ordinary LED.
When the switch is pressed, the LEDs flash for about 5 seconds when the switch is released. and turn off. The circuit takes NO CURRENT after the LEDs have turned OFF.
You can experiment with the value of the electrolytics, the 4k7 and 10k to get the result you want. Use red or green LEDs. Only 2 white LEDs can used in each string for 9v supply

 

[KMoffett]

Here is the type of circuit you need:

View attachment 93178
LED FLASHES FOR 5 SECONDS AFTER BUTTON IS RELEASED
This circuits uses a FLASHING LED - not an ordinary LED.
When the switch is pressed, the LEDs flash for about 5 seconds when the switch is released. and turn off. The circuit takes NO CURRENT after the LEDs have turned OFF.
You can experiment with the value of the electrolytics, the 4k7 and 10k to get the result you want. Use red or green LEDs. Only 2 white LEDs can used in each string for 9v supply

I don't know about the rest of the circuit, but do not put LEDs directly in parallel. The string with the lowest sum of Vf will hog all of the current. Place a 220Ω resistor in series with each string of 2 or 3 LEDs.

Ken

 

[Tony Stewart]

there are situations where running in parallel can cause thermal runaway with current hogging, such as when parts are badly mismatched. Using separate R's rather than sharing is advised if you can be sure by testing each string with a bigger R to meaure the drop or if you know your supply is from the same bin , which is normally done per bag from the factory, but distributors might mix bags.

All my LEDs that I get are matched so parallel strings of several or more is no problem for me. It is common practise for factories to shunt strings in parallel when driving less than rated and much lower risk compared with all in parallel running of a 3.7V LIPo ... Unless you know your LEDs are matched.

In this case, it is trivial to separate Rs for the two strings at 2x values.

Ideally the number of LEDs in the string leaves less than 1 LED drop on the current limiting R, where Ohm's Law applies.