Metku.net

I started trying to replicate your mod myself about a year ago but my studies have been getting in the way of finishing the project but now I've had some more time to try and get back to finishing it and had a few questions about the values for some of the components. Also, I don't have much experience in electronics so please excuse my ignorance

I decided to follow the design around the 4017 chip and 555 timer but couldn't figure out if I needed 1 resistor for ALL the LEDs or 1 resistor for EACH LED. The LEDs I'm planning on using is 1 Bright Red LED and 3 Bright White LEDs. I tried using the LEDCalc but I got confused as to which version I had to use; the Guru, Series, or Parallel model and ended up getting different values for the resistors.
The animation I want is similar to the fire breathing dragon except I wanted the red LED layer always on throughout and the 3 white LED layers to turn on and off, one after the other. How do I achieve this using the 4017?

Can I use just any NPN transistor and Trim POT for the circuit or is there a method I should follow to find a specific one?

I thank you in advance for any help I can get!

http://metku.net/mods/multilayer-animation/4017.png

The picture on the right is the one you should follow. The resistor on top is common for all the leds. Connecting leds in parallel is generally bad but in this scenario only one of the leds will be lit so one resistor works very well. Just use the http://ledcalc.com guru but again, as only one of the leds will be "on" at a time, use 1 as the number of leds.

Pot to alter the speed should be 47kOhm - 100 kOhm model. You may need to add for example a 10 kOhm resistor in series with the pot so that the combined ohms can't be turned to 0. But add this only if there seems to be a need for that.

NPN transistor should be selected by the amount of current you will be signaling on and off. In this case it will be around 20mA per transistor so almost any signal transistor should work well.

Ohhh I see now. So now when I used the guru and I inputted 1 LED and for the Voltage Drop I just used 4v instead of 12v and my result is that I need a 470 Ohm resistor. I'm a little worried that the current is 17ma with that resistor and I need 20ma to power the LED, is this a problem?

Also, can I just connect the Red LED with its own resistor outside of the 4017 circuit and to the battery? I want the Red LED to be on all throughout the animation so I don't know if this would be the right way to do it.

Thanks again!

The red led is a separate circuit as you say. Just use the guru for the red led and treat it as a different circuit.

The transistor does drop the voltage a bit too so you could try a bit higher voltage drop value in the calculator to compensate. Add something like 0.2 - 0.5 volts to the leds voltage drop and see what it gives you.

Okay, I adjusted the LEDcalc like you said and got a better result. I've also added the other LED to the battery out of the timing circuit. I'll try and post a link to the schematic after I've finished putting everything in place. Thank you for your help!