PIC 12F675 Microcontroller based Lantern with Adjustable Brightness

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Emergency lights using fluorescent tubes are inherently inefficient compared to those using LEDs. Here’s a versatile emergency light using LEDs. LEDs are extremely energy efficient and consume up to 50% less power than fluorescent tubes. This circuit is a simple emergency light with 2 Watts output. And it is built around the popular Microchip PIC12F675 micro-controller ICWhen the charger is connected to the circuit, the battery starts charging and green LED6 glows to indicate the charging process. The charging voltage is applied to the battery through diode D1 and resistor R10, which cause a voltage drop of 0.6V across them. Thus the effective charging voltage is about 4.4V, which prevent overcharging of the battery as the terminal voltage of the battery cannot exceed 4.4V. In this design you can control the light output between 0 to 100% using a potentiometer. Which is connected to the micro-controller ADC pin AN3. Reference voltage for the micro-controller is derived from the battery using a TL431 precision programmable reference chip and associated components. The low battery cut-off circuit is built around R2, R3 and C3. Which is connected to the PIC’s ADC pin AN0, when the battery voltage drops below 3.6V the micro-controller automatically switch off the white LEDs and the LED1 blink to indicate the low battery cut-off mode. The brightness of the LEDs are controlled by software PWM (pulse width modulation). The brightness of LED is increased when the PWM duty cycle increases from 0 to 100. All the white LEDs are connected to the battery through series dropper resistors R6 through R9. These resistors are used to limit the current through white LEDs to a safe level. To power LEDs it is required to use a power transistor like a BC639 or BD139 etc, connected to the micro-controller’s pin GP5 through resistor R5.

Features

1. Ideal for camping, fishing, hiking, outdoor activities and also for household and emergency use.
2. LED brightness can be adjustable from 0% to 100%.
3. Battery backup: 4 to 40 hours.
4. Battery charging: mobile phone charger, USB port or 5V solar panel.
5. Battery deep discharge protection with LED indication.
6. Charging indicator.

LED Status	LED6 (green)	LED1 (red)
LED ON	Charging	Lantern ON
LED blinking		Low battery cut-off

 

Parts List
Resistor
R1	560R
R2	10K, 1%, metal film
R3	4K7, 1%, metal film
R4, R5, R11	470R
R6, R7, R8, R9,R10	2R2/0.5W
Potentiometer	10K linear with ON/OFF switch
Capacitor
C1, C2, C3, C4	0.1µF, ceramic-disc
C5	100µF/16V, electrolytic
Semi-conductor
IC1	PIC12F675, Micro-controller
Q1	BC639, power transistor
D1	1N4007, diode
ZD1	TL431, Precision Programmable Reference
LED1	Red, 5mm
LED2, LED3, LED4, LED5	0.5W, white LED
LED6	Green, 5mm
Additional parts
Battery	4V/2Ah lead acid battery
CON1	DC Barrel Socket
8 pin IC base
Common PCB
SMPS based charger or 5V solar panel (maximum charging voltage: 5V DC)

 

Description	Download link
Hex file for PIC 12F675	Download
Schematic diagram	Download