Searched for this last night, didn't find what I was looking for. Ok, so I have a basic understanding of electricity. I can wire up LED's in parralel and in series, and I can do it well enough to avoid using resistors. That's the extent of my circuit understanding. Now, say I want to wire up a series of 10 or 20 LEDs so that a light will run down them. Here, I'll give you an example. 0 is no power, 1 is full power. Simple way: (1)(0)(0)(0)(0)(0)(0)(0)(0)(0) to (0)(1)(0)(0)(0)(0)(0)(0)(0)(0) to (0)(0)(1)(0)(0)(0)(0)(0)(0)(0) Better, more complicated way (probably) (.25)(.5)(.75)(1)(0)(0)(0)(0)(0)(0) to (0)(.25)(.5)(.75)(1)(0)(0)(0)(0)(0) to (0)(0)(.25)(.5)(.75)(1)(0)(0)(0)(0) Now, could anyone explain to me how I might do this? I don't need to be able to change it from my computer, so there's no need for it to be able to interface. Keep in mind that when you use names for those funny little circuit doohickeys, I'll have no clue what your talking about. Thanks for the help guys.
Use a 4017 CMOS counter! Use that and a 555 timer to make it chase the LEDs, and add 1000uF caps in parralel to each LED. As the LED burns, the cap charges up, and when the LEDs power is removed (aka it turns off) the cap will discharge through the LED.
The 4017 is as easy as it gets for the first case. The idea with the capacitors won't work exactly as required due to the inverse log curve of the discharge, but it may be close enough. If it must be exact, you can use a matrix of diodes and resistors, or a PIC. I'd personally use a PIC so if it's necessary to change what it does, re-flashing the PIC will be all that will be necessary.
buy a kit from awierdguy's chop shop. i just got one and it does exactly what you need, 10 leds, but im putting 40 on it. it comes with all parts, and instructions. (9v or 12v) purfect for molex yellow.
This total dummies guide may suit. The 4017 is the black thing with lots of legs. It's an Integrated Circuit. You'll get one from an EElectronics Shop.
Ok... The 4017 is what was commonly refered to by a teacher friend of mine as a "light chaser chip" and it does kinda what it says on the tin. When you feed an up/down signal into one of the pins, it makes each of its 10 output pins get some electricity. When you connect these output pins to LEDs, then they light up each one in turn, then doing the first one again. This is a top-down view of the chip (sadly, i don't have a photo): Code: 16 15 14 13 12 11 10 9 _-__-__-__-__-__-__-__-_ | | ) | | | -_--_--_--_--_--_--_--_- 1 2 3 4 5 6 7 8 Basically, you connect pin 8 to the negative side of the battery, and pin 16 to the positive. This gives the chip power. You then connect pin 13 to the negative (otherwise it won't do anything) and pin 15 as well (we might use this later...). Your up/down signal goes into pin 14, leave pin 12 unconnected, and the other 10 pins are outputs. LA Greg
Best explanation yet. Ok, so a few questions. Say I'm running this off of a snipped up molex. By what you've said I'd connect my, say, 12 volt to 16, and then put 8, 13, and 15 to the ground. Correct? I don't get what the 'up/down signal is'. Now, if the other 10 pins are outputs, where is the other end of each of those circuits?
Thanks... Ok. so you're running it at 12 volts... Well, the outputs are the LEDs that you wanted... except that you can't run them directly at 12v because you'll break them. You need something called a resistor to take away most of it. when you are buying them, ask for resistors that are "680 ohm, 1/4 Watt, 5% tolerance" and you'll get the right ones. They will be little things that look like necklace beads with coloured stripes that have been jammed onto a piece of wire. (I'm assuming that you already have the LEDs) Ok, so you connect the output pins to the resister (doesn't matter which way around the resistor is), and then the other end of the reistor to the LED (the pin nearest the rounded edge). Then connect the flat edge of the LED to the negative. I'll explain the up/down signal tomorrow, because i'm falling asleep here LA Greg
Right, the voltage isn't an issue. It's more likely that I'll set up the individual circuits using the LED's themselves as resistors. Use the right number of LED's in series and your circuit doesn't need resistors.
The up/down signal is the clock of the chip. You have an up/down signal in your PC for your CPU, memory and PCI bus, and it denotes at what speed the thing goes. The same is applicable here, only you don't want a clock going up and down 400,000,000 (400MHz) times a second but just once or twice a second (1 or 2 Hz). 1 Herz is 1 time per second, 2 Herz is 2 times per second, etcetera. So the up/down signal makes the leds light up in sequence basically. There's plenty of ways how to get this signal (commonly called a clock) from an oscillator circuit, but I'm not to sure how quite frankly, I'll leave that to someone more qualified.
I got bored. Left out the component values on purpose, since it's mostly up to you. For the 555 output, the equation for frequency and component values is: f = 1/(.693 x C x (R1 + 2 x R2)) In the schematic, R1 and R2 are RT1 and RT2 (T for Timer). Note that not all 4017 chips can drive your typical 20mA LEDs directly. This one from TI is rated at ±25mA for each output. If you can't get your hands on that one, then you'll need to either buffer the outputs with two transistor array or TTL buffer ICs (you will need two, as the most you're going to get per chip is 8, which won't cover all 10 outputs).
Right, so Landarse, think you might be back around for further explanation? Also, Capacitators. If I put one in series with each LED, that would then cause them to fade after they had recieved power, right? Humm, except, when power came through the wire, wouldn't it first go to charging up the Cap befor it lit the LED, causing it not to light as brightly/not as long?
No, the caps will charge and the LED will light, the combo will only draw more current. You won't notice the difference! I know I don't
Which would then cause them to fade after lighting brightly, although not as exactly as I originally said, which is largely irrelevant, it doesnt need to be exact. I've been reading around and a couple of people mentioned that the cap should be in parralel to the LED. That doesn't really make sense why that would be. Idea? Still would like an explanation of the up/down that I can understand, and how I can get it to work, preferable without more electronics I don't understand. Don't worry guys, I won't screw this up when I start, It's just the starting that I'm working on.
If I recall, you can't run LEDs off any source without a current limiter, because if you say, hook up 4 3volt LEDs to your 12 volt line, they will start drawing huge amounts of current burning themselves out. The reason you need a resistor is to keep them from sucking up tons of amperage. Somebody correct me if I'm wrong.
Not that I've noticed. I've got a 5 volt LED running on just that, a 5 volt line (make that 2 on 2 lines), w/out a resistor, and it's doing fine.
Try measuring the current that LED is drawing, I bet it's way more than the nominal forward current. You must always use a resistor with LED's, even if the supply voltage is the same as the forward voltage of the LED (something in the region of 10 ohms would safeguard you from any voltage fluctuation etc). Well that's just not true. LED's cannot be 'used as resistors' - an LED acts nothing like an ohmic conductor. I suggest you read up about the VI characteristics of a diode.
