# Quick n Dirty answer needed

#### SparkyCal

Mar 11, 2020
849
Normally, i would research this and ask the question in a more informed way. But I am making a special card for my wife's birthday, and U don't have much time left.

I just need to know how to tweak the circuit below, so that it runs on a 9volt battery rather than 5volts.

It is project #2 in this video, which starts at approximately 1:55.

Can anyone help?

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,875
Why don't you try firing up the #2 puppy with a 9V battery and see what happens?

#### Audioguru

Sep 24, 2016
3,656
The datasheet of an LM555 shows on a graph that its output typically goes low to 0.25V. The forward voltage of a modern very bright green LED is 3.0V to 3.6V and its maximum allowed current is 30mA.

Then in that WRONG circuit from a student in India, some LEDs will light properly, most LEDs will instantly burn out and some LEDs will be dim. Most You Tube electronics videos are from students or other kids in India.
The student did not learn that an LED has a wide range of forward voltage and needs a series current-limiting resistor.
The student also did not learn that his 470uF capacitor can be 4.7uF if the resistors are 100k ohms and the battery will last a little longer.

In your circuit, the output low of the LM555 will also be 0.25V. With a brand new 9V battery and a modern very bright green LED then when its forward voltage is the lowest at 3.0V then the series current limiting resistor has across it 9V - 3V - 0.25V= 5.75V and since the wanted current is 30mA then its value is 5.75V/30mA= 192 ohms. Use 200 ohms.

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,875
...Then in that WRONG circuit...
It was all I could do to restrain myself from commenting on that HORRIBLE video. The assembly techniques were bad enough, but perhaps excusable in the interest of minimizing the time required to get something... anything... more or less working so a video could be made. What cannot be excused is the "monkey see, monkey do" presentation of bad circuitry in such a manner that implies "this is the way it is done" when in reality all it demonstrates is "this is what I somehow finally got away with." This sort of thing is MUCH worse than the usual sort of crap one finds on Instructables, where at least sometimes the author tries to explain what is going on.

Did anyone notice that in part three, only six of the seven LEDs were illuminating? Or was that "dark" LED an infrared LED? Jeez, seven LEDs wired in parallel with just one current-limiting resistor?

Thanks, @Audioguru for speaking out on this.

Moderator
Nov 17, 2011
13,637

#### 73's de Edd

Aug 21, 2015
3,607
Hey, youse guys . . . . . . . .

Why don't you try firing up the #2 puppy with a 9V battery and see what happens?

Not exactly what you would expect . . . . since that circuit is dependent upon a static /hi Z AC coupled "ground" thru the power adapter. INSTEAD of the use of a a solo independent / isolated / floating 9 V (or 12) batttery.
When you finger touch the two electrodes induced 60~ hum / pulses picked up from house wiring into your body and outted thru a fingertip is triggering the 555 I.C. latch function working in conjunction with the static AC circuit return. .

. . . . . . .some LEDs will light properly

Now I can't examine and evaluate the RED LED, for why it is not functioning.
But just look at the 6 other operating LEDS and you can easily see the two WHITE ones light brightly.
While the 4 other ERSATZ GREENS AND BLUES are not actually being bonafide R & G electro chemically constructed units.
Instead, they are ALSO being WHITE units that are then depending upon a tinting of their outer mold casting for the coloring aspect . . . . . . but, then performing quite dismally, in that respect..

My wife would be thrilled with this rinky dinky bottle cap construction as a gift ? ? ? ? . . . . . . possibly back when she was 4.

73's de Edd . . . . .

#### AnalogKid

Jun 10, 2015
2,860
I just need to know how to tweak the circuit below, so that it runs on a 9volt battery rather than 5volts.
No changes are needed - maybe.

1. There is no current-limiting resistor in series with the LED, so the LED should be much brighter.

2. The blink rate is about 60 times slower than it should be for the components in the video.

3. The chip in the first part where he is connecting jumpers across the bottom side, and the chip in the second part where he attaches the components - are not the same chip.

Consider the very real possibility that the video is intentionally faked as a troll prank.

ak

#### Audioguru

Sep 24, 2016
3,656
The kid from India has 19 thousand subscribers. You Tube pays him 19 thousand rupees when all subscribers look at the ad then look at one of his videos. We are not his subscribers but maybe he is also paid by You Tube when we look at the ad then look at his awful video.

#### 73's de Edd

Aug 21, 2015
3,607
1. There is no current-limiting resistor in series with the LED, so the LED should be much brighter.

In assemblage . . . .at the final 11th hour . . . just at the onset of closing the bottlecap clamshell together . . . .there is a 100 ohm resistor from the LED commons to a white wire to making a final connection into pin 3 of the 555.

#### AnalogKid

Jun 10, 2015
2,860
. . .there is a 100 ohm resistor

ak

#### Audioguru

Sep 24, 2016
3,656
In the third circuit, the red LED does not light because its forward voltage is less than the white, green and blue LEDs causing all the unlimited current to burn it out the instant the battery was connected.
In the video I did not see a 100 ohm current limiting resistor but I saw a 1k resistor not connected on one end.

#### SparkyCal

Mar 11, 2020
849
Well..it is pretty clear that i picked the wrong circuit to follow ;-) Maybe I should reframe what i would like to do.

I am drawing a small heart on a 2 X 2.75 inch circuit board.

I'd like to light the heart up using red LEDs.

Inside the heart, I'd like to have my wife and my initials. I am thinking the initial should flash and i will probably use Yellow and Blue or perhaps Yellow and White LEDs. Her favorite colour is purple, but I doubt I have purple LEDs

So, looking for a simple schematic...perhaps using the 555 timer, as I have lots of those

#### Audioguru

Sep 24, 2016
3,656
To flash a number of LEDs from a 555 you need a power supply or a huge battery. What is your choice? What voltage?
How many red LEDs around the heart and how many LEDs flashing the initials?
What are the forward voltages of the different LED colors you will be using?

#### AnalogKid

Jun 10, 2015
2,860
Your question still is not clear. When you say:

"Inside the heart, I'd like to have my wife and my initials. I am thinking the initial should flash"

are you talking about drawing the initials with strings of LEDs, or backlighting the initials printed on paper, or something else?

ak

#### SparkyCal

Mar 11, 2020
849
I think I will need 20 LEDSs (all red LEDs for the heart). It is for a card, so it will have to work once or twice. Not somethingnthat will be left on for a long time.

The initials, I am thinking of runnings with a separate circuit or two, if required.

#### AnalogKid

Jun 10, 2015
2,860
The video segment you posted is for one (1) LED, not 20. That is a significantly different problem. What is your skill set for wiring together all of the parts? This can be done with a single bipolar 555.

The forward voltage for a typical red LED is around 1.8 V. Electrically you could have five strings of LEDs, with four LEDs in series in each string, all driven by the 555 output. Each string gets its own current limiting resistor, something around 75 ohms. Mechanically you can place the LEDs anywhere; they do not need to be in a 4 x 5 grid.

ak

Last edited:

#### Audioguru

Sep 24, 2016
3,656
1.8V red LEDs in series strings of 4 LEDs with a 75 ohm resistor and five of these strings driven by a 555 slasher circuit will show how quickly a little 9V alkaline battery will slowly dim the LEDs then die.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,637
I am drawing a small heart on a 2 X 2.75 inch circuit board.

I'd like to light the heart up using red LEDs.
Something like this? Plenty of space inside for a picture of the lovely couple.

D
Replies
0
Views
873
Day Brown
D
K
Replies
9
Views
1K
Don Foreman
D
K
Replies
1
Views
1K
CFoley1064
C
Replies
26
Views
2K
Replies
0
Views
1K