This desktop sized 12 inch Christmas tree is bought from a houseware store in December 2002. It used to have two 2.5 volts wired flashing bulbs inside the base (one red and one clear), powered by 2 AA size cells. In 2016 I modified the circuit with 2 5mm color fading LEDs (150 ohms resistor is installed in series for each LED), and also the power supply to USB. In the photo the tree is powered by my Asus router's USB 2.0 port. Since the LEDs are the same model, which means both of them have the same color sequence, but the running speeds are slightly different. Last week I modified the circuit again by adding a simple SCR-based delay circuit to the slower LED, which delays the lamp to turn on by a second. Please refer to the second image for the circuit diagram. The gate resistor and capacitor controls the trigger time of the SCR, the resistor must be less than 100 kohms or the SCR will never turn on. For the output, a PNP driver transistor is recommended for more stable output; since the output is open drain only, NPN transistor will not work.
Chi Ho Fung
This desktop sized 12 inch Christmas tree is bought from a houseware store in December 2002. It used to have two 2.5 volts wired flashing bulbs inside the base (one red and one clear), powered by 2 AA size cells. In 2016 I modified the circuit with 2 5mm color fading LEDs (150 ohms resistor is installed in series for each LED), and also the power supply to USB. In the photo the tree is powered by my Asus router's USB 2.0 port.
Since the LEDs are the same model, which means both of them have the same color sequence, but the running speeds are slightly different. Last week I modified the circuit again by adding a simple SCR-based delay circuit to the slower LED, which delays the lamp to turn on by a second. Please refer to the second image for the circuit diagram.
The gate resistor and capacitor controls the trigger time of the SCR, the resistor must be less than 100 kohms or the SCR will never turn on. For the output, a PNP driver transistor is recommended for more stable output; since the output is open drain only, NPN transistor will not work.
4 months ago | [YT] | 1