Wednesday, September 25, 2013
A Bedside Lamp Timer Circuit
30 minutes operation, Blinking LED signals 6 last minutes before turn-off
The purpose of this circuit is to power a lamp or other appliance for a given time (30 minutes in this case), and then to turn it off. It is useful when reading at bed by night, turning off the bedside lamp automatically in case the reader falls asleep... After turn-on by P1 pushbutton, the LED illuminates for around 25 minutes, but then it starts to blink for two minutes, stops blinking for two minutes and blinks for another two just before switching the lamp off, thus signaling that the on-time is ending. If the user want to prolong the reading, he/she can earn another half-hour of light by pushing on P1. Turning-off the lamp at users ease is obtained by pushing on P2.
Circuit diagram:
A Bedside Lamp Timer Circuit Diagram
Parts:
Resistors
R1 = 1K
R2 = 4K7
R3 = 10M
R4 = 1M
R5 = 10K
Capacitors
C1 = 470µF-25V
C2-C4100nF-63V
Semiconductors
C1 = 470µF-25V
C2-C4 = 100nF-63V
D1-D4 = 1N4002
D5 = 5mm. Red LED
IC1 = CD4012
IC2 = CD4060
Q1 = BC328
Q2 = BC547
Miscellaneous
P1,P2 = SPST Pushbuttons
T1 = 9+9 Volt Secondary 1VA Mains transformer
RL1 = 10.5V 470 Ohm Relay with SPDT 2A 220V switch
PL1 = Male Mains plug
SK1 = Female Mains socket
Circuit operation:
Q1 and Q2 form an ALL-ON ALL-OFF circuit that in the off state draws no significant current. P1 starts the circuit, the relay is turned on and the two ICs are powered. The lamp is powered by the relay switch, and IC2 is reset with a positive voltage at pin 12. IC2 starts oscillating at a frequency set by R4 and C4. With the values shown, pin 3 goes high after around 30 minutes, turning off the circuit via C3. During the c6 minutes preceding turn-off.
The LED does a blinking action by connections of IC1 to pins 1, 2 & 15 of IC2. Blinking frequency is provided by IC2 oscillator at pin 9. The two gates of IC1 are wired in parallel to source more current. If required, a piezo sounder can be connected to pins 1 & 14 of IC1. Obviously, timings can be varied changing C4 and/or R4 values.
Source : www.extremecircuits.net
Friday, March 15, 2013
Ballast and Starter Fluorescent Lamp
Ballast
- Provide the initial installation of the electrodes in order to provide free electrons in large numbers
- Provide a potential wave big enough to hold a spark between two electrodes
- Preventing the occurrence of an increased flow of sparks that exceeds a certain limit for each lamp size.
Starter
Starter
on a fluorescent lamp consists of a small glass balloon filled with
noble gases. Inside the bubble there are two metal electrodes as dual
filament. The distance between the two electrodes are arranged with a
certain distance so that the starter will turn on voltage of 100-200 V.
Starter switch serves as the delay time (time delay switch) are connected in parallel with two-foot fluorescent lamp.When the fluorescent lamp is connected to the voltage of tissues, then in a short time starter filament is connected (on) and then decide again if the lamp has been lit with a stable NE. At the time of the filament is connected, a large current will flow through the ballast from the power grid, then to the lamp electrodes, wire electrodes and the other starter, for subsequent return to the network. The existence of these currents will make the incandescent lamp electrodes and removing electrons.
Meanwhile, the voltage at the starter has been lost, so that the starter went out and become cool. Both dual metal electrodes in the starter going straight back and decided that the current is flowing. Because of the sudden termination of this, the ballast will be raised an electromotive force is quite high. Shock voltage is in series with line voltage. When raised at the right time, the voltage at the two filament lamps TL will be high enough to ignite the filament-provided tube filaments are hot enough.
In the first cycle of the tube is not already on the events as described above will be repeated, until the tube lights up. After the fluorescent lamp is lit, the starter will be parallel with the lamp. Therefore, the voltage on the lamp voltage is lower than the starter, the starter will remain extinguished.
To reduce the spark at the spark electrode bi-metal can be mounted a small capacitor in parallel with the starter. Installation of condenser is also able to improve the termination of the current in the starter and reduce radio interference.