The mini pumpkin LED face

Step 2 Circuit Design

The blue and red LEDs are connected in parallel with a resistor to ground as shown in the diagram. Since here we are using one resistor for multiple LEDs in parallel be sure to use one that has the proper power rating.

• The voltage drop across these blue and red LEDs are 4.5V and 2.2V respectively.
• The voltage across the resistor with a 9v source and the blue LED in series is 4.5V
• The voltage across each resistor with a 9v source and the red LED in series is 6.8V
• The power dissipated by both resistors is ~90mW

Tips

If you are going to try different LED and resistor configurations here are some guidelines.

• Connecting your resistors in parallel rather than in series is a lot easier since you have to do the soldering inside the pumpkin.
• If you use blue LEDs you will not be able to hook them in series with a 9v source since there is typically a 4.5v drop across the high intensity type.
• If you are hooking the LEDs up in parallel like we are here and you use a lower valued resistor (<100ohms) you will probably need one with a higher power rating