Flashing LED Battery status Indicator

Signals when an on-circuit battery is exhausted 5V to 12V working voltage

A Battery-status Indicator circuit will also be useful, mainly to observe portable Test-gear units and equivalent devices. LED D1 flashes to apparel the customers attention, signaling that the circuit is operating, so it's going to no longer be left on by using mistake. The circuit generates about two LED flashes per second, however the mean present drawing might be about 200µA. Transistors Q1 and Q2 are wired as an unusual complementary astable multivibrator: each are off 99% of the time, saturating best when the LED illuminates, in this case contributing to keep very low current consumption. 

Circuit diagram :

Flashing-LED Battery-status Indicator Circuit Diagram

The circuit will work with battery supply voltages within the 5 - 12V vary and the LED flashing will additionally be stopped at the desired battery voltage (comprised within the four.8 - 9V worth) by way of adjusting Trimmer R4. This vary can also be modified via altering R3 and/or R4 worth relatively.

When the battery voltage methods the onerous price, the LED flashing frequency will fall suddenly to alert the consumer. Obviously, when the battery voltage has fallen under this price, the LED will stay completely off. To maintain steady the exhausting voltage price, diode D1 was once brought to compensate Q1 Base-Emitter junction changes in temperature. The use of a Schottky-barrier device (e.g. BAT46, 1N5819 and the like) for D1 is mandatory: the circuit is no longer going to work if a common silicon diode just like the 1N4148 is used as an alternative.

Parts :

R1,R7__________220R  1/4W Resistors
R2_____________120K  1/4W Resistor
R3_______________5K6 1/4W Resistor
R4_______________5K  1/2W Trimmer Cermet or Carbon
R5______________33K  1/4W Resistor
R6_____________680K  1/4W Resistor
R8_____________100K  1/4W Resistor
R9_____________180R  1/4W Resistor
C1,C2____________4µ7  25V Electrolytic Capacitors
D1____________BAT46  100V 150mA Schottky-barrier Diode
D2______________LED  Red 5mm.
Q1____________BC547   four5V 100mA NPN Transistor
Q2____________BC557   45V 100mA PNP Transistor
B1_______________5V to 12V Battery provide
Notes :

• Mean current drawing of the circuit can be lowered further on by using elevating R1, R7 and R9 prices.

Source : Red Circuits