The minimum supply voltage for an ordinary 555 is 4.5V so use 6V.

The base of the transistor needs a current-limiting resistor in series with it to prevent the 555 from blowing up. With a 6V supply use 68 ohms.

600 times per second will look like the LEDs are continuously turned on. 20 times per second is very fast flashing. Maybe you want 10 times per second.

Ok. Thanks for the warning on blowing up the 555, will add resistor there and watch the current.

You are right, 600 times per second should be 600 times per minute, or 10 flash per second.

 

Actually my CMOS 555 projects work down to 3V, though they would need modified to drive that many LEDs (nothing that complex)...

The 555 Projects

This design would work well with your LEDs...

CMOS 555 Long Duration Red LED Flasher

 

Actually my CMOS 555 projects work down to 3V, though they would need modified to drive that many LEDs (nothing that complex)...

The 555 Projects

This design would work well with your LEDs...

CMOS 555 Long Duration Red LED Flasher

Hm.. CMOS 555 timer looks like an idea.. The local store here got TLC555CP in stock, a CMOS 555 timer. Also they got BD135 NPN power transistors, so will purchase those tomorrow, along with a couple of capacitors with different values, and test this circuit.

I made a schematic based on your schematic, attached to this post. The Q2 transistor will consist of a BD135 power transistor, and will perhaps put a resistor between Q1 and Q2 in case, as a whopping 0.76A is going to pass right by the 555 timer, and not sure where that current plan to travel

I got a question about your CMOS 555 Long Duration Red LED Flasher schematic, the ground symbol, what is that for? Isn't it redundant as the minus poles of the battery is included in this schematic? It's my understanding that the ground symbol quite often is the minus pole of the battery?

 

You have the right idea, but there is a problem. Lets see, 10ma X 76 is still ¾A. If the transistor could handle it it might work.

Why not use 6X AA batteries? They would still be small, and using 9V (with a 100Ω resistor for every 4 LEDs) would get the current down to ¼A. The same circuit would also work at that voltage.

I think you're getting this down though.

 

You have the right idea, but there is a problem. Lets see, 10ma X 76 is still ¾A. If the transistor could handle it it might work.

Why not use 6X AA batteries? They would still be small, and using 9V (with a 100Ω resistor for every 4 LEDs) would get the current down to ¼A. The same circuit would also work at that voltage.

I think you're getting this down though.

This is working great, thanks for the help!

I have some minor questions, out of curousity.

What do you mean with if the transistor can handle it? Heat or not enough gain?

I have experimented with a 18 LED setup, will try 76 next week. Resistors R1 and R2 are changed down so off time from the output of the 555 timer is shorter, it flashes with a bright strong light, about 5 times a second. Also added an extra resistor between Q1 and the 555 timer to prevent blowing the timer up.

When I measure current going from the collector of tranistor Q2 to the LEDs, it's about 150mA. If current come straight from the battery it's 160mA. I have tried with three different transistors, both ordinary, semi and full power transistors, and also tried to vary the current to the base, from 0.2mA to 10mA, still the same, less current through the transistors, than straight from the battery. Is it something I don't know about transistors, like resistance or leak?

Also, the C2, the 100uF capaciator, what is it for? Avoiding spikes and using power more effective? Is it safe to ditch it as it takes some space and I am only using the light for no more than 5-10 minuttes?

The 18 LEDs circuit setup I use is included in this post.

 

Basically if you push too much current through the transistor it will blow like a fuse. A 2N2222A is rated for .6A, you are going to try .75A. It might work, it might not. The fact the LED pulses are so short work in your favor.

The capacitor makes a huge difference. You can try to run it without it, but even in the short time it will make it's lack felt. It provides the extra current when the batteries can't. As with all things, try it and see.

You are pushing the limits on this project, but then, I don't see a real problem with it as long as you understand things may go out at inconvenient times. Extra batteries (voltage) would make a difference here.

I've had about 1 hour sleep in the last 24 hours, and am feeling the lack. When I have time I'll post some other ideas.

 

Ok, I'll keep the 100uF capacitor, it makes sense. It isn't that big, and I am already on the limit here. The Q2 transistor is a BC 368 with 1mA and 20V. It's a medium power transistor, but results are much the same with other transistors.

Will experiment with this stuff more, but just a bit puzzled about the drop in current when it goes through the transistor, compared to going straight from the battery, but it's not a big issue. I suspect it can have something to do with lower voltage, as the voltage of battery drops after a while, making the gain in the transistor lower. It can also be that the 555 circuit is stealing some amps.

If someone of you know, I would be glad to know.

 

The drop through the transistor is actually reasonable. We are pushing a design that was intended for a lot less current way past its limits.

I keep saying this, but you really need 6V or 9V (I prefer 9V). Lots of good things happen with more voltage to drive it. You can go down to AAA batteries if you need to.

The reason is simple, you can put LEDs in series with each other. Once you do that the currents go down fast. Extra voltage means a CMOS 555 works much better too, they can go down to 2V, but the have quite a few restrictions that become major, such as the output they can drive. I used it to my advantage in CMOS 555 Long Duration Minimum Parts LED Flasher.

If you are going to try to drive all 75 LEDs with one transistor (and another transistor driving it) you need a power model, something in a TO220 case style. It will not need heat sinks, just the ability to stand current.

Going with the current 3V model (and a power transistor for Q2) you can modify the driver as follows.

I have to compliment you, you are very quick to learn, and have the most important of all attributes, perseverance.

When you finish this I hope you post pictures.