Skema Rangkaian|Electronic Schematic Circuit Diagram

Fridge Door Alarm Circuit

16 October, 2009 (12:13) | Other Circuits | By:

Beeps if you leave open the door over 20 seconds

This circuit, enclosed into a small box, is placed in the fridge near the lamp (if any) or the opening. With the door closed the interior of the fridge is in the dark, the photo resistor R2 presents a high resistance (up to 200K) thus clamping IC1 by holding pin 12 high. When a beam of light enters from the opening, or the fridge lamp illuminates, the photo resistor lowers its resistance (less 2K), pin 12 goes low, IC1 starts counting and, after a preset delay (20 seconds in this case) the piezo sounder beeps for 20 sec. then stops for the same lapse of time and the cycle repeats until the fridge door closes. D2 connected to pin 6 of IC1 allows the piezo sounder beeping 3 times per second.

Circuit diagram:

Fridge Door Alarm Circuit Diagram

Parts:

R1 = 10K
R2 = LDR
R3 = 100K
R4 = 100K
D1 = 1N4148
D2 = 1N4148
Q1 = BC337
C1 = 10nF-63V
C2 = 100uF-25V
B1 = 3V Battery
IC1 = 4060 Ripple Counter & Oscillator IC
BZ1 = Piezo Buzzer Incorporating 3KHZ Oscillator
SW1 = Miniature SPST Slider Switch

Notes:

Connecting D1 to pin 2 of IC1 will halve the delay time.
Delay time can be varied changing C1 and/or R3 values.
Any photo resistor type should work.
Quiescent current drawing is negligible, so SW1 can be omitted.
Place the circuit near the lamp and take it away when defrosting, to avoid circuit damage due to excessive moisture.
Do not put this device in the freezer.

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Tags: circuit, door, fridge, photo resistor, resistor r2, resistor type, V BatteryIC

DC or AC Voltage Indicator Circuit

16 October, 2009 (12:13) | Other Circuits | By:

Detects 1.8 to 230 Volts DC or AC, Minimum parts counting

This circuit is not a novelty, but it proved so useful, simple and cheap that it is worth building. When the positive (Red) probe is connected to a DC positive voltage and the Black probe to the negative, the Red LED will illuminate. Reversing polarities the Green LED will illuminate. Connecting the probes to an AC source both LEDs will go on.
The bulb limits the LEDs current to 40mA @ 220V AC and its filament starts illuminating from about 30V, shining more brightly as voltage increases. Therefore, due to the bulb filament behavior, any voltage in the 1.8 to 230V range can be detected without changing component values.

Circuit diagram:

DC or AC Voltage Indicator Circuit Diagram

Parts:

P1 = Red Probe
P2 = Black Probe
D1 = 5 or 3mm. Red LED
D2 = 5 or 3mm. Green LED
LP = 1220V 6W Filament Lamp Bulb

Note:

A two colors LED (Red and Green) can be used in place of D1 & D2.

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Tags: ac source, circuit, filament lamp, Red, V AC, voltage, voltage indicator, W Filament

Mobile Cellphone Battery Charger Circuit

16 October, 2009 (12:13) | Other Circuits | By:

Stops charging when battery is full charged, Portable unit

Charging of the mobile phone, cellphone battery is a big problem while traveling as power supply source is not generally accessible. If you keep your cellphone switched on continuously, its battery will go flat within five to six hours, making the cellphone useless.
A fully charged battery becomes necessary especially when your distance from the nearest relay station increases. Here’s a simple charger that replenishes the cellphone battery within two to three hours. Basically, the charger is a current-limited voltage source. Generally, cellphone battery packs require 3.6-6V DC and 180-200mA current for charging.
These usually contain three NiCd cells, each having 1.2V rating. Current of 100mA is sufficient for charging the cellphone battery at a slow rate. A 12V battery containing eight pen cells gives sufficient current (1.8A) to charge the battery connected across the output terminals. The circuit also monitors the voltage level of the battery. It automatically cuts off the charging process when its output terminal voltage increases above the predetermined voltage level.

Circuit diagram:

Portable Cellphone Battery Charger Circuit Diagram

Parts:

P1 = 20K
P2 = 20K
R1 = 390R
R2 = 680R
R3 = 39R-1W
R4 = 27K
R5 = 47K
R6 = 3.3K
R7 = 100R-1W
C1 = 4.7uF-25V
C2 = 0.01uF
C3 = 0.001uF
D1 = 5.6V-1W Zener
D2 = 3mm. Red LED
Q1 = SL100

S1 = On/Off Switch
B1 = 1.5vx8 AA Cells in Series
IC1 = NE555 Timer IC

Circuit Operation:

Timer IC NE555 is used to charge and monitor the voltage level in the battery. Control voltage pin 5 of IC1 is provided with a reference voltage of 5.6V by zener diode D1. Threshold pin 6 is supplied with a voltage set by P1 and trigger pin 2 is supplied with a voltage set by P2. When the discharged cellphone battery is connected to the circuit, the voltage given to trigger pin 2 of IC1 is below 1/3Vcc and hence the flip-flop in the IC is switched on to take output pin 3 high. When the battery is fully charged, the output terminal voltage increases the voltage at pin 2 of IC1 above the trigger point threshold.
This switches off the flip-flop and the output goes low to terminate the charging process. Threshold pin 6 of IC1 is referenced at 2/3Vcc set by P1. Transistor Q1 is used to enhance the charging current. Value of R3 is critical in providing the required current for charging. With the given value of 39-ohm the charging current is around 180 mA. The circuit can be constructed on a small general-purpose PCB.
For calibration of cut-off voltage level, use a variable DC power source. Connect the output terminals of the circuit to the variable power supply set at 7V. Adjust P1 in the middle position and slowly adjust P2 until LED (D2) goes off, indicating low output. LED should turn on when the voltage of the variable power supply reduces below 5V. Enclose the circuit in a small plastic case and use suitable connector for connecting to the cellphone battery.

Cellphone Battery Charger Circuit’s LED Status

Note !

This circuit was tested with a Motorola make cellphone battery rated at 3.6V, 320 mAH. In place of 5.6V zener, a 3.3V zener diode was used. The charging current measured was about 200mA. The status of LED is shown in the table.