Please help :LED strobes

[dryden_burton]

hello i need a LED strobe circuit that will flash 2 sets of LEDs right and left
I need it to flash the right side twice then the left side twice.

RR LL RR LL RR LL RR LL RR LL RR LL RR LL


it would be nice if it could run on a 9v

 

[Nigel Goodwin]

hello i need a LED strobe circuit that will flash 2 sets of LEDs right and left
I need it to flash the right side twice then the left side twice.
it would be nice if it could run on AAs or a 9v

A PIC12F675 (8 pin PIC), two LED's, two resistors, and a power supply decoupling capacitor is all that's required. You can program the PIC for any flash rate or sequence you want, and even increase the number of channels to more than two.

You could power it from four AA NiCd or NiMh, giving a 4.8V supply.

 

[dryden_burton]

any schematics would be appreciated (sp)

 

[Nigel Goodwin]

any schematics would be appreciated (sp)

It hardly needs one, but this is one way you could do it - just needs the software for the chip writing (which should be a simple job, it's a very simple requirement).

 

[audioguru]

C'mon, let's use buffer transistors to get some current through those LEDs! A maximum current of only 3mA through the LEDs surely won't make them "strobe" nor flash brightly. I suggest feeding them with 15ms pulses of 25 to 30mA. Their "on" time will be so short that the battery should last a long time.

 

[dryden_burton]

anything that doesn't need programing

or even a kit from a company with all the parts or something maybe

 

[Nigel Goodwin]

anything that doesn't need programing

As you can see from the circuit I posted above, a PIC makes the design extremely trivial - doing it in hardware would be many times more complicated - it's the double flashing which causes complications.

 

[audioguru]

Just a Cmos oscillator/counter like a CD4060 and a gate should make the blink-blink, and another couple of gates should toggle the sides. It's fun to select different pins on the counter and see (hear?) the duration and frequency change. I made a repeating beep-beep gadget like that many years ago, I hid it and drove everyone crazy trying to find it. I'll post it when I find it.

 

[bonxer]

If you're wanting something that doesn't require programming, use a 555 timer from Radio Shack. You just have to hook up two resistors and a capacitor to set the oscillation frequency. Although it only has a single output, it will work for your case too. Tie one LED's anode to your voltage source, a resistor to the cathode, and connect that to the 555 output call that A. Then connect the anode of a second LED to the 555 output, then a series resisitor to the cathode, and then that resistor to ground.
Call that B. A square wave will be coming out of the 555. Everytime it is low, it will provide a ground at the output, so A turns on, and B turns off. Then when the pulse rises, A turns off, and B turns on. Repeat. So there you have two alternating LEDs. Look up 555 timer connection diagrams and frequency calculations on the mighty google. You can change my +5v to a +9v in the diagram and use a battery. A 555 can use 9v easily, so you don't even need a regulator. Just make sure the resistors in series with the LEDs are able to limit current through them to no higher than 30mA (sometimes 25) based on whatever voltage you decide to use.

 

[dryden_burton]

can some one explain to me how and where (which pin number) to connect the timing resistors and capacitors

thanx for all the help you guys are great

 

[gerty]

Here's one that'll do what you want (LL-RR ) It's a 4093b clock going to a 4017 counter. Two of the outputs are tied together with diodes for each side. You can change the pot or cap for different speeds, the values I show are what works for us on the Rescue vehicles.
I had to shrink it down to fit the screen, any questions, just ask ..
Hope this helps

 

[gerty]

Sorry 'bout the double pic..Just noticed that drawing doesn't show current limiting resistors for leds. I used Superbrightleds #1157 bulbs for this and they have their own resistors built in. If you use discrete leds you will have to include the current limiting resistors in the led circuit, I'd put them between the led and ground. The value of the resistor will depend on the led , but it'll probably be around 470 ohms for 12 volts..

By the way, Nigel is right, a pic would do more with less components..

 

[audioguru]

Hi Gerty,
Ouch! No current limiting resistors for the LEDs? Maybe with your 19 LEDs the transistors are straining to provide enough current for them all. If you used only a couple of LEDs per side, they would blow-up in nano-seconds.

 

[gerty]

Audioguru..see above..I used led 1157 'bulbs' with built in resistors, each 'bulb' has 19 leds in it..You're right, without resistors they would die a quick and horrible death ..

 

[audioguru]

Yeah, but I bet your circuit would be fine without the resistors(if the LEDs were all matched). With 19 LEDs the straining transistor would limit the current.

 

[bonxer]

Try this. You are powering the circuit with a 9v battery. The 555 timer outputs a square wave to the complimentary transistors, driving the diodes with 470 ohm resistors to limit the current to around 15 mA each. Sound good? Here's a huge write-up on the 555 timer, with calculation formulas for getting the frequency, how long the pulse is high, low, all that good stuff.
**broken link removed**

 

[audioguru]

Hi Bonxter,
What are the transistors for? You already showed the same circuit without them.
The datasheet shows that the 555 is easily capable of driving a couple of LEDs high and low since its output is rated at 200mA.

Besides, your PNP transistor will never turn off because the positive-going output of the 555 is an NPN darlington (Q21 and Q22) so its output cannot go closer than about 1.2V from the positive supply. About the only thing the transistors will do is smoke and drain the battery! :lol:
Here's the 555's schematic showing Q21 and Q22:

 

[bonxer]

I couldn't find a source or sink current limit in the 555 datasheets. All I sould find was a 15mA max current it will use from the supply, so I went with that, as I noticed the original request was for two LED driven on one cycle, and two LEDs driven on another. I just threw all that stuff in the simulator and it worked well. I hadn't taken into account the real world internals might prevent the operating of my transistors I added. Its been a long time since I used a 555 after discovering the PIC and their 12F625 goodness.

 

[dryden_burton]

is there a kit i can order with all the parts and the pcb

btw sometimes it will be running 4 LEDs 2 on the Right and 2 on the Left and sometimes it will be runing 6 LEDs 3 on the Right and 3 on the Left

thanx

 

[Nigel Goodwin]

is there a kit i can order with all the parts and the pcb

You are aware that these 555 designs don't meet your requirements?.

You wanted two flashes each side, this will only give one!.