Each LED is hardwired with the appropriate resistor for 4.5v

But your schematic shows two LEDs in series and a resistor. Do you have one or two LEDs in series???

Will I have to rewire the strands if I step up to 6v?

Maybe. The current will be higher when the voltage is higher so the 56 ohm resistor values must be increased to limit the current.

or could I toss a resistor before the strand that will (when added with the already hardwired one) adjust for 6v?

Yes. Adding another resistor in series with the 56 ohm resistors is the same as increasing the value of the 56 ohm resistors.

 

so what i did for the REDs is take two Red LEDS, put them in series, add the resistor and solder. This becomes a 'set'. I then made 6 of these. (12 leds total). I then took each set and ran them in parallel with each other.

For the blues, each led gets its own resistor, and I only ran 6 leds off of 4.5V.

The Setup:
I have two strands of blue at 6 LEDs/strand
And one strand of red at 12LEDs.

The goal/idea was to alternate the reds, 6 and 6 since those go on my backpack and need more visibility.

The blues go on the frame and would just flash or double flash.

 

Red LEDs need 1.8V to 2.2V each plus some voltage for the current-limiting resistor. Then the 4.5V battery voltage is too low, especially when it quickly drops to 3.6V.
Blue LEDs need about 3.5V each plus some voltage for the current-limiting resistor.

I hope you have wide-angle LEDs because some cheap ones have a very narrow angle to make them appear brighter but only when they point directly at somebody who might run into you. If they don't point directly at somebody who might run into you then they are invisible.

 

They are wide angle, I also did a test run and had them solid on for 3hrs or so. You can see the bike from way way far away. Very very bright. just want to add the alternating, flashing to increase visibility.

If the voltages are incorrect, then why does the lower strand light up fine at full brightness? This is what is confusing me. I am temped to just scrap the top strand and run the lower strand by itself as a flasher. Alternating would be nice but if its just not going to work with the setup then I guess I'll have to move on.

Could someone help me with this circuit, (redesign) for 6v along with one with a double flasher setup using a CD4017. I would simply double flash one strand and then the other by hooking up to the 0,2 5,7 pins.

Thanks for the patience. I am a learn as I go kind of person so this is very informational lesson for me.

 

May want to check local laws, flashing red/blue lights to the rear may be illegal there. Unsure why, but Law Enforcement tends to think anything blue and blinking is exclusively theirs, especially if they point forward.

Rule here is only white/yellow forward, red/yellow (no white) to the rear. Not sure where blue would fit in.

 

Yes Blue and Red alternating will most likely be illegal.

The California Vehicle Code only mentions the use of brightness and location.

The reds are attached to my backpack and are set at a steady pulse rate. (facing to the rear)

The blues are attached to my main front frame bar and the back angle bars. They too are going to pulse at a steady rate and are facing down (illuminating the ground and frame)

As long as they are not pulsing alternating next to each other or are brighter than visible at 300ft, It is fine. I have whites facing forward as well for forward road visibility.

The reds might be the only ones blinking just so they don't get over shadowed by the blues that is if this circuit gets working.

Should I try to switch out the NTE159 with the TIP31? or just stick with the pulsing on the low output from pin 3.

 

Did you switch to a 6V supply?

4 AA batteries aren't much more to carry around than 3.

 

have not yet had the chance to play with the actual setup. I think I will switch, but at the same time am curious why the bottom strand still lights up brighter than the top. (for my knowledge) At this rate, I may keep the setup and just use the bottom strand only (since its blinking at full brightness) and just remove the High output transistor setup all together.

 

6V on the power supply will reduce current and allow you do do more (such as blue LEDs). However, I promised a circuit, and I will deliver.

The reason one strand is brighter than the other is specific to CMOS 555. This chip is quite good, but it has some idiosyncrasies you need to understand. First, the lower the power supply the less current it can provide. At 3V the output current is so low that a resistor is not needed for the LED, an almost unheard of situation (the CMOS 555 is the resistor). Second, no matter what the supply voltage it only sources 1/10 the current than it sinks. One supply rail on the output is much weaker, so it can not drive the transistor adequately.

In coming up with these circuits several solutions presented themselves. There are some good ideas for you there too. Did you read the CMOS 555 Long Duration series in the The 555 Projects? They practically scream for your application, especially the last one, the flyback version. It can handle all the LEDs you want, and at any color, at 4.5V. I have had excellent success with it on other designs.

LEDs are efficient, but there more you light the greater the current draw from the batteries, and the shorter the life. TANSTAFL

Before I can do a good job designing, I need real number of LEDs you are planning on using. So how many, 5, 6?

Blue is always much brighter than red given quantity and current brightness. If you want equivalent brightness between colors plan on more red LEDs.

Since I don't know your electronics background we'll go over some basics. I must have the Vf of the LEDs, probably each individual LED in some cases. How familiar are you with Ohm's Law?

The reason is when designing so close to the chest if I make the wrong assumption the circuit might not work as predicted. Going back to Vf, it is possible you might be able to have two red LEDs in series, but a simple variation among them will kill the idea. Or if you have a blue LED (which have a wider variation), one LED will be dim while the other bright, simply because of variations in the LEDs themselves. You can compensate for it on the circuit (this concept is called test select) by you have to know why you're doing it to some extent. I get the feeling you know the basics, but if I'm wrong telling me know would save us some time.

Designing conservatively means allowing for all variations, and compensating for them. This almost always increases circuit complexity and parts count (such as using the flyback circuit). As a hobbyist I'd rather test select LEDs and resistors.

 

OK, first drawings. Example A & B might work, example C & D will work. This configuration occurred to me while I was drawing the first. The reason for all the transistors is the CMOS 555 (a 7555 is an alternate brand name) can not output very much current, and you need a lot of current comparatively speaking. The transistors buffer this, but more than one is required to do the job.

These circuit will pull around 0.1A (100ma) from the battery, which isn't very friendly. Each LED is getting 20ma.

I'll be back with the flyback version later.

 

This is great! I checked out the long duration write up and I see now how two transistors will influence the current gain. Right now the circuit is pulling around 240 or so ma from the battery (2000mah) so to me 100 is great!

For now, I am thinking of alternating two sets of red strands. 2.2 forward voltage 24ma max current. Each strand will have 6 leds. 12 leds total in the project.

The secondary project is two strands of Blue Leds. 3.2 forward voltage, 20ma max current. Each strand will have 6 Leds for 12 leds total in the project.

As I mentioned earlier, the leds already have appropriate resistors for 4.5V attached.

I like the circuits. I will try them out. I also like the long duration circuit and have most of the parts already.

Thanks again for the help.Finally understanding how it all fits together. (and while working on this, came up with a new project idea, but I'll save that for a different thread)

 

The 100ma was for the LEDs shown. More LEDs, more current. TANSTAAFL

When I have more time I'll show you an alternate driver that will be a lot more efficient (the flyback version).

 

yes. Technically though I shouldn't push pass 288-300ma with the leds (12leds) which should work for me since, and to throw another dun dun dun into the mix, I am planning on using rechargeables which i know have less than 1.5v. something more like 1.2v per battery (AA). I can simply recharge when they expire or drop too low to flash the circuit.

So am I to use example A/B and just add more LEDs to it? or were you going to make up another schematic? Between those and the long duration red flasher I think i got how it works. I do need to know though what the flyback version means. Not quite sure.

thanks

 

I am planning on using rechargeables which i know have less than 1.5v. something more like 1.2v per battery (AA). I can simply recharge when they expire or drop too low to flash the circuit.

You forgot to do the arithmatic.
Three Ni-MH cells at 1.2V each produce only 3.6V.
Two red LEDs in series at 2.2V each need 4.4V.
Then the LEDs will not light.

They cannot make LEDs all have the same forward voltage. Their forward voltage is "typically" 2.2V but could be anywhere from 2.0V to 2.4V or as stated in the datasheet.

 

true that. I realized that once I submitted that comment. I guess I will either go with 4AA's or just stick with 3AAs and go non rechargeable.

 

Due to a busy life it took a lot longer to draw this than usual, but combined with your circuit in post #18 you should be able to go down to 3V batteries (Vcc) with no problem.

Explanation of this circuit can be found at this address.

http://forum.allaboutcircuits.com/album.php?albumid=152&pictureid=1161

 

But the minimum supply for an ordinary 555 is 4.5V, not 3V. With a supply of only 3V then a Cmos 555 might not have enough current to drive the transistor.

 

Noted, I thought of this on my way to work. I'll correct the schematic tomorrow.

Other than that, this design has been verified, and the base resistor was 1KΩ, so that particular argument doesn't fly.

 

I build and verified this schematic, it works. I had to make a few changes, and learned a few things in the process.

 

Great! Just a few questions, what is the digital input and L1. I checked the link and didnt find that there. I will use this circuit for the reds and other blue strands. Using the lo output of the 555 to trigger the PNP transistor is working for the other set.

thanks again for your help with this! I learned a lot from this project and look forward to using this knowledge in future projects.