9V LED Timer Circuit Question

Your big mistake is to think that you get 1.5v out of a single cell.
You do when they are brand new, but to get any decent life from them you have to run them down to 1 volt or even less (0.8 being about the minimum useful voltage at the end of their life). Keep it simple add more cells.
Similarly a 9v battery will be at about 6v as it approaches the end of it's useful life.

Don't feel bad about this, I'm met highly paid telecom consultants who made the same mistake
Del

well it's weird, with most of these said 1.5V cells I actually get 1.63-1.67V then instead of using the theoretical 3V from 2 cells I changed it to 3 cells and now I get roughly 4.94V. and then, as the voltage goes through the circuit, it lets go enough to reach 3.25 to power the modified LED (typical christmas LED) to give off the right amount of light, and I'm sure that even after months of daily use when the batteries start to die, it'll still have quite a bit of light to give off. thank you for the advice. perhaps after finishing this I will make a new charging circuit to charge rechargeable batteries when I travel down hill, and act as breaks just like in most hybrid cars.

? Curious, if you change to an LED that requires more power, wouldn't that decrease or completely eliminate any need for concern about overloading the LED or circuit itself? the 8-pin chip is actually the TLC555, that was all radioshack had. The video, I'm pretty sure, did not ground the circuit, so the LED did not turn all the way off. I changed the potentiometer to a resistor of 55.4K and changed the LED to a christmas LED that gives off a wider angle of light. Then to finish it all I added a 3rd 'AA' battery, making the circuit start with 4.94V and let the LED get 3.25V. also the circuit will only be on for a maximum duration of 30 seconds, and I doubt overheating could occur then. but I thank you very much for your advice. just recently I went back into radioshack and found some ancient chips on the wall, all 8-pin, err I guess 16 pins total (much more rectangular than the smaller chips, and longer). all are 74HCT---N chips, the exception being the 74HCT574E chip. any ideas on what I could build with those for starter circuits?

I only just noticed you put a question against my post! Remember the title of this thread is "9V LED Timer..." and the video has 9V battery. If you have TLC555 that is good, it has more overcurrent protection than basic 555. The TLC555 in the 8 pin pack which is about 0.3 x 0.4 inch can survive 1 watt heating at 25 Celsius air temperature (Data sheets call that the Absolute Maximum Rating) - but it also comes in versions so small only machine placing on PCBs is practical and have lower heat tolerance. If you use 9V at the 0.2 amp current limit of the TLC555 with an LED that drops 2 volts at 0.2 amp, that gives 7 volts lost through the TLC555. Now 0.2 amps x 7 volts = 1.4 watts - the IC WILL fail in continuous operation if the LED is continuously lit. But 0.2 amp x (4.5 - 2) = 0.5 watts, so with a 4.5V battery you can play safely Unless you leave your bike in the sun and the timer gets too hot to touch! As other posts write, there is no point in using a higher voltage to drive one LED. You wrote "change to an LED that requires more power", if it were an 0.5 amp RATED one, this would be safe driven by a TLC555 (which has current limit about 0.2 amp. built-in). But if you wanted to drive it at 0.5 amp, a TLC555 cannot do it. Unfortunately, 74HCT...N chips come in so many varieties, some very complex counters. The 74HCT00 is the most basic being 4 logic gates, each with two inputs. But you can do a lot with a 555, there are whole books about circuits you can use with it. If you just use "Search All of CR4" box to find "555", there are dozens of threads about it. Search for 555 data sheets at www.datasheetarchive.com, the Signetics one has some application circuits for monostable etc others do too.

To get (any) 555 to give roughly 50:50 timing, therer are several ways to correct this, I tend to use a diode to short out one of the resistors (when using 2 - Ra and Rb)....

If needed I will try and find an example circuit for you.....

You also need to buffer the output and drive two transistors in opposition, one for each LED. That will allow a lower working voltage to be used....

I'm still working on transistors, electronics just baffle me so much.... just the other day I re-learned how capacitors work, and that was a shock, the first time I had it very wrong... the original circuit design only has it hooked up so the LED won't turn off completely, but this problem is solved just by connecting pin 1 to ground. thank you very much for your advice. that would be great for a sample circuit! if there is any way to simplify this basic 50:50 timing at the same frequency of a left/right turn signal blink, that would be much appreciated!

It looks like Jaxy is just using garden variety LEDs. A trick I learned was to use a 4050 CMOS buffer between the 555 and the LEDs. It saved having to use dropping resistors. Come to think of it though, I am not sure about running it off 9 volts. This was back in the days when virtually all logic ran off of 5 volts.

Bill

well I changed the circuit to 4.94V roughly with 3 'AA' batteries, so 9V are out of the picture now. I tend to think of 9V batteries as only smoke detector batteries, otherwise I like less voltage and cheaper batteries. thank you very much for your advice.

I will go back through and individually go through each comment tomorrow, but right now I'm typing a short reminder and update. as it turns out, the TLC555 chip base circuit I'm using was not actually grounded, so it was using the LED to drop excess power, and not allowing it to turn off. once grounded, it creates 50:50 time lapse on/off, which is exactly what I needed it for. for using 9V, it can power anything, and for 3V (give or take a few tenths of a volt) it can power a high brightness white LED just perfectly. unfortunately I found a small flaw: in order to fully replicate a turn signal (in particular one that gives light to more than 180 degrees of view) you need to have a better LED, one contoured to wide viewing angles. in a search for single or double packages of modified LED's I found nothing, but I did find some spare leftover christmas lights and now I will use those, except they require more power. so for the christmas lights I think I will use 4.5 volts (or rough equivalent) for the circuit, I think that will do nicely. in the video of the original post the demonstrator also uses a 100K potentiometer for adjusting the time of the flash and for how long. for this I'm going to replace it with a resistor of similar or exact resistance to place into a permanent circuit. once all is said and done I will probably make a video for it. thank you for reading and helping, again I will reply to each post tomorrow when I have more time