LED strobes

[risp73]

Do you have schematics for LED strobe: 2 seconds continuous light and than blinking with f=3 Hz?
I tried with two 555's but without success. How monostable 555 can trigger bistable one?

 

[Torben]

Do you have schematics for LED strobe: 2 seconds continuous light and than blinking with f=3 Hz?

How long should the 3 Hz strobing last? Indefinitely? i.e. the circuit receives power or an "on" signal, then lights the LED for 2 seconds, and then emits a strobe every 3 seconds until turned off? Or should the cycle repeat?

I tried with two 555's but without success. How monostable 555 can trigger bistable one?

Just talking off the top of my head here, and assuming that the circuit should behave as I described above, but maybe use a transistor to sense when the original 2-second-on pulse ends, and start the 3 Hz strobing 555 with that. Google for "555 timing calculator" to help with setting up the 555 3 Hz strobe circuit. Note that I don't know that you can do a true strobe with a 555, but a quick blink should certainly be possible.



Torben

 

[risp73]

How long should the 3 Hz strobing last?
Torben

LED lights 2 seconds, and then emits a strobe every 3 seconds until turned off.

... maybe use a transistor to sense when the original 2-second-on pulse ends, and start the 3 Hz strobing 555 with that.
Torben

How can I start 3 Hz strobing 555? Something with pin 2?

 

[ericgibbs]

LED lights 2 seconds, and then emits a strobe every 3 seconds until turned off.

How can I start 3 Hz strobing 555? Something with pin 2?

When you say 'emits a strobe every 3 secs' How long is each strobe?

Is it say a 1sec strobe or just a quick flash?

Can you fill in your Location?

 

[risp73]

Square wave output with duty cycle ≈ 50%
(LED, not xenon)

 

[ericgibbs]

Square wave output with duty cycle ≈ 50%
(LED, not xenon)

hi,
I know its not a xenon strobe.

Are the LED On/Off times in this drawing what you require?

 

[risp73]

How can I start IC2 with falling edge on pin 3 IC1?
See attachment,

 

[Torben]

LED lights 2 seconds, and then emits a strobe every 3 seconds until turned off.

How can I start 3 Hz strobing 555? Something with pin 2?

I think one way might be to put an NPN with the collector to the 555's GND pin, the emitter to circuit ground, and the base to an inverter attached to the line powering the LED so that when the LED lines goes low, the inverter makes that high, turning on the transistor and therefore turning on the 555.

Note that I'm just a hobbyist in a hurry as I'm running out the door for a couple of days, I haven't actually tried this or even simulated it, and others here probably have more valuable insights into the problem. I can see where there might be some problems with the idea I've outlined above, but something along these lines might be doable. So don't be discouraged if you try this and it doesn't work.

Good luck! I'll check this thread again when I get back on Tuesday or so--I'm interested to see what you come up with.


Torben

 

[Roff]

Try this circuit.

 

[Torben]

Hi again,

Turns out my idea had just about every potential problem I had thought of and some I hadn't. I also couldn't get Ron's idea to work (at least, not in LTSpice), but I did manage to get one idea working. See the attached image. The other attachment is the LTSpice file if you want to simulate it.

Note that this idea works (or is meant to; I haven't tried it in the real world) on power-up only; that is, when power is applied, you get the LED on for 2 seconds, after which the LED should flash for 0.1 second every 3 seconds until you remove power. It should work with a low-going trigger if you remove D4, R9, and C3 and just put the trigger into the left side of C5.

Anybody have any thoughts? Too complicated? Seems like there must be a simpler way to do this.

Anyway, that's my idea. Hope it helps!


Torben

 

[Leftyretro]

Hi again,

Turns out my idea had just about every potential problem I had thought of and some I hadn't. I also couldn't get Ron's idea to work (at least, not in LTSpice), but I did manage to get one idea working. See the attached image. The other attachment is the LTSpice file if you want to simulate it.

Note that this idea works (or is meant to; I haven't tried it in the real world) on power-up only; that is, when power is applied, you get the LED on for 2 seconds, after which the LED should flash for 0.1 second every 3 seconds until you remove power. It should work with a low-going trigger if you remove D4, R9, and C3 and just put the trigger into the left side of C5.

Anybody have any thoughts? Too complicated? Seems like there must be a simpler way to do this.

Anyway, that's my idea. Hope it helps!


Torben

Much better if you implemented it with a PIC, then timing and behaviour could be optimized. Also less total components and costs. PICs are the new logic chips, it's time to put away the 555s

Lefty

 

[audioguru]

Hi Torben,
You have the collector and emitter reversed for the PNP transistors Q1 and Q3. The emitters should be connected to the positive supply.

Since Q2 doesn't have a current-limiting resistor in series with its base then it will blow up. Q2 also needs a resistor from its base to ground to turn it off.

The diodes don't do anything.

 

[Torben]

Much better if you implemented it with a PIC, then timing and behaviour could be optimized. Also less total components and costs. PICs are the new logic chips, it's time to put away the 555s

Lefty

Well, yeah, but then I don't learn as much about what the actual electricity is doing. I've been programming various things for most of the last couple of decades so that's no longer as much of a challenge. I kind of like old approaches to things--but I totally agree that if it were for production or something then then the microcontroller would be the way to go. It just feels like every problem has a controller thrown at it (probably because they do the job cheaply).


Torben

 

[Torben]

Hi Torben,
You have the collector and emitter reversed for the PNP transistors Q1 and Q3. The emitters should be connected to the positive supply.

Since Q2 doesn't have a current-limiting resistor in series with its base then it will blow up. Q2 also needs a resistor from its base to ground to turn it off.

The diodes don't do anything.

Excellent. Not the screwups, but the pointers. Thanks!


Torben

 

[Leftyretro]

Well, yeah, but then I don't learn as much about what the actual electricity is doing. I've been programming various things for most of the last couple of decades so that's no longer as much of a challenge. I kind of like old approaches to things--but I totally agree that if it were for production or something then then the microcontroller would be the way to go. It just feels like every problem has a controller thrown at it (probably because they do the job cheaply).


Torben

Cool! Does that mean your up to designing a vacuum tube implementation? Think of all the electrical learning that would bring you Actually there were/are switching type tubes called thyristors I think, worked on some Air Force equipment that used them to switch code wheels on a cool off-line crypto machine called a KL-7. Size of a small typewriter had about six switching tubes.

Lefty

 

[Torben]

Cool! Does that mean your up to designing a vacuum tube implementation? Think of all the electrical learning that would bring you Actually there were/are switching type tubes called thyristors I think, worked on some Air Force equipment that used them to switch code wheels on a cool off-line crypto machine called a KL-7. Size of a small typewriter had about six switching tubes.

Lefty

Ha! Nope. Not yet, anyway. But I do want to do something cool with tubes at some point--if only because they look cool and it would seem that many people will pay out the nose for anything with a tube in it. Some company put out a computer sound card a few years back with a tube on it. Note that I don't really think that it was a very good idea. . .

Don't get me wrong--I'm all about learning the controllers too. I did my first 8051 projects last year (Knight Rider-ish LED sweep and an ultrasonic rangefinder) and I'm really excited about what I could do with them (or rather, more advanced chips like the AVRs and PICs). The original poster mentioned 555s specifically, though, and I was just trying to work out where Ron (now Roff) was going with his design.

A while back I did a foosball scoreboard with 555s, TTL logic, and discrete transistor logic. It's huge, has way too many parts, and sucks juice like there's no tomorrow (OK, under an amp, but still way too much). I keep meaning to clean up the design enough to post it but I'm also really busy learning to be a dad. And I also intend to do the microcontroller version--eventually.


Torben

 

[Torben]

OK, family is in bed and I sat down (with a book and a calculator this time) and worked in audioguru's fixes. I also changed some resistor and capacitor values to be standard values. This circuit should be more reliable.

And as Lefty noted, you could do this with fewer parts and more configurability and precision with a microcontroller, if you have access to a programmer.


Torben

 

[Nigel Goodwin]

Actually there were/are switching type tubes called thyristors I think,

No, thyristors are semiconductors - you 'may' be thinking of thyratrons?.

 

[audioguru]

Hi Torben,
Now your circuit looks good.

I have never seen a 500 ohm "standard" resistor. 470 ohms and 510 ohms are standard.

 

[Roff]

I gotta defend myself. Better late than never. I was out seeking gold with my metal detector yesterday (found 2 little dinks).
Anyhow, my design works, unless I misunderstood the requirements. Here's the .ASC file for LTSpice.