# Make an LED blink project.

#### woozycactus

Joined Jan 4, 2021
104
So I have a small project that I want to do that I am not sure if it is even possible. The timing does not need to be perfect but, the idea is, I want to make a
LED blink twice in about every 1 to 2 seconds, Here is the catch, no Arduino and no chips. Is it possible to do this with just caps, transistors, resisters ect.. ?

After I or someone figures that out, I want to make 2 LEDs do the same thing but alternating. So LED1 will blink twice then LED2 will blink twice and reset.
I already have a circuit to make 2 LEDs alternate using resisters, caps, and 2 transistors with no logic.

#### Tonyr1084

Joined Sep 24, 2015
7,785
We'd love to help you. But generally, we aren't an engineering service. If you take a stab at it we can then direct you to the solution. In the end you learn something you can take with you for (hopefully) the rest of your life. But if we just give you the answer then all you've learned is to lean upon others skills.

Yes, a flashing LED is possible without the use of chips. Is this a homework assignment?

#### dl324

Joined Mar 30, 2015
16,731
I already have a circuit to make 2 LEDs alternate using resisters, caps, and 2 transistors with no logic.
Making LEDs blink with no logic is easy. Counting without logic IC's can be done, but you'll have to implement discrete counters.

What is your motivation for not using IC's?

#### Tonyr1084

Joined Sep 24, 2015
7,785
I want to make a LED blink twice in about every 1 to 2 seconds.
Here, greater definition is needed as well. Do you want ON for 1 second, OFF for one second, repeat? Or do you want on for 90% of the time with a 10% off (blink)? Using a 555 I did exactly that. Halloween Pumpkin with red LED eyes that would blink off for an instant and on for about 5 seconds, giving the allusion that it's watching you. But you said "No chips". That's why I ask if this is homework.

#### woozycactus

Joined Jan 4, 2021
104
We'd love to help you. But generally, we aren't an engineering service. If you take a stab at it we can then direct you to the solution. In the end you learn something you can take with you for (hopefully) the rest of your life. But if we just give you the answer then all you've learned is to lean upon others skills.

Yes, a flashing LED is possible without the use of chips. Is this a homework assignment?
well looking at other posts that didn't seem to be an issue with someone asking for help that has no idea on how to make something, I didn't think it was an issue but let me rephrase. I have already built a circuit to make 2 LEDs alternate without logic. Is their a way to make LED1 blink/strobe twice very quickly, then wait about 1 to 2 seconds and then blink/strobe twice again. In the end product I want to make LED1 blink/strobe twice then LED2 blink/strobe twice then to LED3 and so on. Its not a homework assignment. It is for my son who we got a power wheels fire truck for xmas that comes with lights that are just hollow and we want to give him some lights that looks a little more realistic than just strobing...

#### MrChips

Joined Oct 2, 2009
30,509
Yes it can be done without ICs.
One pulse every second is relatively easy.
Two pulses every second is about three times more difficult.

#### woozycactus

Joined Jan 4, 2021
104
Making LEDs blink with no logic is easy. Counting without logic IC's can be done, but you'll have to implement discrete counters.

What is your motivation for not using IC's?
First its a very tight space that I have to work with. second, I don't have any chips at this time, I have an assortment on the way. The main reason is everywhere I search for anything similar chips are being used but then i find some article and like only one that has a diagram to not use them. So really its just to see if it can be done.

#### Tonyr1084

Joined Sep 24, 2015
7,785
So I take it this project should have a flashing light arrangement like you said, "Strobe". It's far easier to achieve your goal using chips than just discrete components and transistors. Given that a chip is generally a whole bunch of transistors (or MOSFETS, depending on the technology), using transistors only is possible. But I suspect it will take far greater work and real estate.

#### woozycactus

Joined Jan 4, 2021
104
So I take it this project should have a flashing light arrangement like you said, "Strobe". It's far easier to achieve your goal using chips than just discrete components and transistors. Given that a chip is generally a whole bunch of transistors (or MOSFETS, depending on the technology), using transistors only is possible. But I suspect it will take far greater work and real estate.
Well the one that i build just uses 2 transistors, 2 caps, 4 resisters which 2 are just for the LEDs that's it. So i was hoping it would be some amount of components to add and just set up a difficult way. If its really that many more components then I guess its not going to work.

#### Tonyr1084

Joined Sep 24, 2015
7,785
its a very tight space
For a child's toy, you don't need to have the most realistic flashing. Yeah, it would be great to make it look authentic, but not necessarily required. Someone here on this website knows how to use a single transistor, I think a 2N2222 and a reverse biased LED with a timing cap to get a flashing rate going on. I don't recall who has that, but you can google something like flashing LED light circuits and might be able to find a simple, cheap way of doing exactly that. A flashing strobe like light. Combine that with a super bright LED and you should be good to go. And even if the strobes are not 180˚ out of phase, I don't think the child is going to mind. My kids LOVED the stupid stuff I'd make for them.

#### Tonyr1084

Joined Sep 24, 2015
7,785
Well the one that i build just uses 2 transistors, 2 caps, 4 resisters which 2 are just for the LEDs that's it. So i was hoping it would be some amount of components to add and just set up a difficult way. If its really that many more components then I guess its not going to work.
Post your schematic and we can go from there.

#### MrChips

Joined Oct 2, 2009
30,509
The truth is that it can be done with a single IC on a PCB no bigger that ½ x ½ inch, with sound output included.

#### Tonyr1084

Joined Sep 24, 2015
7,785
A quick search on the internet turned up the circuit I was describing. I've even breadboard built it just to see if it really worked. Changing the cap changed the frequency with which it flashed.

 Now I'm wondering if Q1 can be replaced by a zener diode.

#### woozycactus

Joined Jan 4, 2021
104
Post your schematic and we can go from there.
Not very good and drawing these.

#### Tonyr1084

Joined Sep 24, 2015
7,785
Perfectly find drawing. That schematic will alternate between left and right. If I understood your opening statement you want the left to flash twice then the right to flash twice and repeat over a period of about 2 seconds. Is that correct?

How big is the toy? Can you post a picture with some frame of reference such as a common coin like a penny or whatever common currency you use? Or a picture with a ruler, inches OR millimeters - etc.?

#### dl324

Joined Mar 30, 2015
16,731
Not very good and drawing these.
That circuit won't work very well because the bias current for the transistor that's on will likely be enough to make the LED that should be off be dimly lit.

One hack is to put a resistor across the LEDs so they won't turn on with small currents. The other is to have the LEDs be across the C-E and have the saturation voltage turn the LEDs off.

If you replace the transistors with N channel MOSFETs, it will work.

#### sghioto

Joined Dec 31, 2017
5,369
I don't have any chips at this time, I have an assortment on the way.
What are they?

#### Tonyr1084

Joined Sep 24, 2015
7,785
Another thought - can you place the circuitry elsewhere and just run the wires to the light bar of the toy? That way you open yourself to many more possible solutions if you're not as restricted for space. The whole thing doesn't need to reside inside the light bar.

#### woozycactus

Joined Jan 4, 2021
104
That circuit won't work very well because the bias current for the transistor that's on will likely be enough to make the LED that should be off be dimly lit.

One hack is to put a resistor across the LEDs so they won't turn on with small currents. The other is to have the LEDs be across the C-E and have the saturation voltage turn the LEDs off.

If you replace the transistors with N channel MOSFETs, it will work.
it works pretty well..