![]() ![]() 003 mA, especially for a battery with the characteristics we are using (4.5 Ah capacity), is a very good value. See, for example, if there were 4 resistors of 1KR, according to Ohm's Law, the loss would be: U = R * i => 12V = 4000R * i => i = 12V / 4000R => i = 3mA 3 mA constantly, but as we chose 4 resistors of 1 MR, we have: U = R * i => 12V = 4000000R * i => i = 12V / 4000R => i = 0.003 mA 0.003 mA of constant loss. What changes is the amount of current that would be lost in that system. Note that there could be 4 resistors of 5 KR, or 4 of 1 KR, or 4 of 330 R, or even 4 of 1 R, since, for the calculation of the voltage divider, the final result would be the same, calculate yourself. The value of the resistors was made according to the current drain, which naturally occurs in our load level measurement system. It is the time to explain the two points that remain unexplained, the first is why the resistors of 1 MR. This output voltage (V_OUT) will always be a fraction of the input voltage (V_IN) in relation to the values of resistors R1 and R2. ![]() The sensor itself, consists of a voltage divider, as seen in Figure 2, is a simple arrangement of two resistors and the ability to read the voltage between them. As there will be two batteries in series, the values we will use are 12 V, 4.5 Ah capacity, fluctuating from 13.5 to 13.8 V, in cyclic from 14.1 to 14.4 V, total.Īt the other end, we will use an Arduino analog port, which in the case of Arduino Uno, operate at a resolution of 10 bits and 5 V.įigure 2 - Scheme of a Voltage Divider and its formula There is some information that is crucial to build this circuit, the first is the properties of the battery in use, for example, for this experiment we will use two sealed 6 V lead acid batteries, 4.5 Ah capacity, in fluctuation from 6.75 to 6.90 V, in cyclic from 7.05 to 7.2 V, each. There is a simple way to measure this, so let's get to practice. To adapt this circuit to your specific needs, determine the minimum voltage necessary for proper equipment operation and multiply it by 2/3 to obtain the required zener voltage.One of the main concerns of a project that will be powered by batteries is knowing exactly when they are about to discharge. If the voltage at 2/3 Vcc exceeds the zener voltage, it inhibits the 555 timer's functionality. The key element here involves connecting a zener diode between pin 7 of the 555 timer and the ground.ĭuring standard operation, pin 7 oscillates between one-third and two-thirds of the supply rail voltage (Vcc). The circuit comprises a 555 timer configured in the bistable mode, serving as the driving mechanism for the LED. The flashing function initiates at approximately 7.5 V, while the LED won't illuminate at all below 2 V. The provided component values are optimized for a 9 V operation. This 555 low voltage indicator circuit is designed to activate an LED when the power supply voltage exceeds a specific threshold and to make it flash when the batteries require replacement. IC 555 Pinout 555 Low Battery Indicator with Flasher Z1 = zener diode, having voltage lower than the battery voltage. 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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