Louie,
You may not have seen it, but I posted the values that you should use in Audioguru's 555 timer circuit in order to get 1/2 second between switching to the next LED

There is one additional capacitor that was not addressed attached from pin 5 to ground; normally this is an 0.001uF to 0.01uF cap - however, you can also use a 0.1uF cap on it.

OK, you need to find out what your LEDs really drop as far as voltage. That number can vary quite a bit from batch to batch. Let's test several of them and find out.

Your LEDs are rated for 20mA at somewhere between 2.8v and 3.6v. You have a 5v supply. Let's calculate a "safe" value of resistor to use in testing them.

The LEAST voltage they will drop is 2.8. Let's subtract that from your power supply voltage:
5V - 2.8V = 2.2V
Now we need to determine what value of resistor will guarantee a maximum of 20mA current across 2.2V:
R = E / I
R = 2.2V / 20mA
R = 2.2 / 0.02
R = 110 Ohms
So, if you connect a 110 Ohm resistor in series with your LEDs that you are testing with a 5V power supply, you should not exceed their rated 20mA current.

To make sure, use your multimeter in series with the 110 Ohm resistor and and the LED across the power supply to measure the current; use the 200mA range.

After you've measured the current, set your multimeter to 5v or 10v range, and connect the LED in series with the 110 Ohm resistor across your power supply. Measure the voltage drop across the LED. It should fall within the range of 2.8 to 3.6 volts.

You should measure several more LEDs to make sure this is pretty consistent. Use the lowest reading you measured, and return to the part where the "safe" resistor was determined above; this time using the lowest measured voltage across the LEDs.

 

is 1/4 1.6m ohm and 1/4 3.9m ohm going to work just asking because you didnt give me the size

OK, sorry about that. You can figure out the wattage using Ohm's Law. At most, there will be 5V across either of the resistors.
P = E2/R
P = 25/1.6M
P = 0.000015625 Watts
Since the other resistor is much larger, we don't have to bother calculating it.
Yes, you certainly can use a resistor rated 0.25 Watts in this situation.

Also, you should be aware that in electronics, "1.6m Ohm" and "1.6M Ohm" are very different. The lowercase "m" indicates "milli", or 1/1000 of 1 Ohm, where "M" is for "Mega", or millions of Ohms. Proper use of upper and lower case is essential.

 

dont have leds yet should be here tomorrow but as for the 100uf cap that connects to positive and ground what do i use there being that i have a 5v source

 

That is for if your power supply wires are more than a few inches long. Normally, all integrated circuits should have a capacitor of around 0.1uF across their Vcc/Vdd and ground/Vss terminals. This helps smooth out transients (ie: voltage spikes) when a circuit suddenly changes states. If the wires to the power supply are of considerable length (a few feet) a much larger capacitor is used where they join the circuit board.

 

o ok my wire from power supply to circuit board will be around 2-4 inches so should i use .1uf again

 

OK, so measure your LEDs when they get delivered. Now at least you have a procedure on how to test them.

If you do not have the exact resistor, you can use the next larger size (IE, instead of a 110 Ohm use a 120 Ohm) but the higher the value of resistor, the less light the LED will put out. Don't use a smaller resistor though, or you will quickly destroy the LED.

 

o ok my wire from power supply to circuit board will be around 2-4 inches so should i use .1uf again

Yes, get in the habit of using 0.1uF capacitors across the power and ground pins of your ICs. You circuits will be much more reliable.

 

i also forgot to mention i have 2 1k ohm potentiometer's i thought maybe that could control speed would this work

 

i also forgot to mention i have 2 1k ohm potentiometer's i thought maybe that could control speed would this work

I am afraid that the 1k Ohm potentiometers would be far too low in value to work for this project. They will be useful in future projects though.

 

well let me know what type i need and i will see if i can get it

 

OK.

If you used a 47K Ohm resistor for Ra, a 500K Ohm pot for Rb, and a 2.2uF capacitor for C, you would have a range of about 2/3 Hz to about 12 Hz.

You would also need a 3K Ohm resistor to put in series with Rb, to make sure you didn't go below 3k Ohms. Otherwise, if you did, the circuit would not operate properly; you might even damage it.

As long as they are all rated at least 1/10 Watt, you'll be fine.

 

Hi Audioguru,

Would it be possible to adapt your 6v ultra bright LED chaser circuit to work with 1.5v x 1.2mm filament bulbs, instead of LED's? If so, could you help with a modified circuit?

Bru

 

My project is designed for LEDs, not light bulbs. Most of the high power of light bulbs is wasted as heat. Each light bulb must be driven from a transistor that has a voltage divider to reduce its voltage to only 1.5V.

 

Thanks for the info, Audioguru. I'll put a help request on the forum and see if anybody has a working schematic I can try.

 

well got in the hard drive. leds and some resitors should be in but not the one sgtwookie recommended me to use.

 

i cant believe i actually was able to read the schematic and make the circuit work it works great on my breadboard now just have to figure out how i will make it fit neatly on a circuit board and thanks for everyones especially sgtwookie