The moment the red LED starts glowing and gets illuminated sharply the green LED completely shuts down, making the conditions clear to the user regarding the battery which may be assumed to be fully down and gone below the dangerous low voltage mark. Until the set lower threshold is not reached, the above pin of the IC is allowed to receive the specified amount of positive potential sustaining the green LED in a blinking mode, which in turn indicates that everything is well with the battery. The IC 555 is wired in its conventional astable mode so that the connected green LED produces a flashing effect as long as its reset pin#4 stays above a certain positive voltage level via the red LED and the series 10k resistor. The low battery stage produces only a low voltage indication and the relevant LED shines only until the level dips below the set threshold, this might well keep the user guessing if the actual or the normal condition of the battery was OK and if the battery was functioning correctly in the meantime.įor satisfying the above results, a flashing LED indicator could be seen attached with the low battery section, using our old compatriot IC 555. This stage has been elaborately explained HERE, you may want to go through it for further details. The left side stage which uses two BJTs is a simple low battery indicator circuit, the red LED lights up as soon as the supply voltage falls below the predetermined threshold level, as set up by the 47K preset. The figure below shows the circuit configuration of the proposed battery voltage status indicator circuit through a flashing LED indicator. Is there any way to add a second LED that will flash to indicate power is there and working? The low battery indicator circuit is working fine but I have to put my meter across the terminals in order to check it is still working. On your website because I am growing vegetables in a raised bed and have erected 12v electric fence to prevent slugs and snails eating my plants.įor this I am using an old car battery which is holding a good charge. The set circuit is now ready to be attached with the battery in question, whenever the battery voltage reaches the 11.4V mark, the LED would light up, providing the required low battery information.Hi, I found and built your “ Low Battery Indicator Circuit Using Two Transistors Only” Now the preset may be glued by some permanent adhesive for preventing the setting from getting disturbed. Next, the preset should be adjusted such that the LED just lights up. Suppose, the specified lower threshold is 11.4V for a 12V battery, the applied sample voltage can be fixed at 11.4V and applied to the circuit. The above setting can be done manually by applying a sample voltage to the circuit imitating the lower threshold level. The battery voltage is allowed to reach pin#2 of the IC via the preset, which must be manually set such that voltage at pin#2 just falls below the 1/3rd of the zener voltage when the battery voltage reaches the specified lower threshold. Therefore in the proposed design the supply pin of the IC is fixed at some reference level using a zener diode. The above fact also indicates that pin#2 responds with reference to the supply voltage applied at pin#8 of the IC, which implies this voltage at pin#8 should be clamped to some constant level. We all know regarding the basic characteristic of the IC 555 when it's being used in the comparator mode: if pin#2 is subjected to a potential lower than 1/3rd of the Vcc, the output pin#3 goes high. The circuit functioning may be understood with the following points: An over discharge could mean a permanent damage to the battery.Ī novel little low battery indicator circuit can be learned here, which incorporates just a single IC555 and a few resistors, it's a simple "plug and watch" kind of circuit. Many electronic circuits such as emergency lights, battery chargers, UPS systems, flashlights etc essentially require a low battery indication feature in order to avoid over discharge of the involved battery.
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