Friday, 3 April 2009

220V Line Powered LED Lamp

To connect a single LED lamp to the 220V AC line, the minimum need are a series a high voltage capacitor and a resistor. A diode also in parallel with the LED in reverse polarity connection.

The diode prevents reverse voltage breakdown of the LED. The resistor is needed to prevent in-rush (surge) current to the capacitor if from OFF (discharged). An additional resistor in parallel to the capacitor to bleed the charged voltage when the circuit is OFF to prevent electric shock.

Computing for values:
I(led) = 0.02
Xc = V/I(led) = (220-3)/.02 = 10850
Cmin = 1/(2*pi*Xc) = 1/(2 *pi * 60 * 10850) = 0.24uF = 0.22uF nearest value

Friday, 16 January 2009

Nicad Charger by IC CA3140E

This is easy circuit charger batt Nicad.
For batt 1.2V. 

Monday, 5 January 2009

The second circuit simulates the siren of an American police car. It uses two 555 timers in the circuit. The 555 on the right is wired as an alarm tone generator and the second 555 timer on the left is wired as a low frequency astable timer which generates a ramp waveform of about 6 seconds that is buffered by the transistor and again used to frequency modulate the tone generator. The transistor is used to help strengthen the signal to the speaker