![]() Size comparison of alkaline batteries (left to right): C, AA, AAA, N, PP3 (. Note that, due to the high input voltage, the power dissipated will be a bit more than 300mW, so a 1/4W resistor wont do. Size comparison of alkaline batteries (left to right): C, AA, AAA, N, PP3 (9-volt). The closest value youll find will probably be 820. The main feature of this circuit is its very low stand by current consumption. Am I missing something here? This circuit is currently on a bread-board by itself, I just wanted to figure out if my idea worked. R V I V+ VLED ILED 18V 2V 20mA 800 R V I V + V L E D I L E D 18 V 2 V 20 m A 800. The following post describes a simple low battery indicator circuit by using just two inexpensive NPN transistors. My LED just stays on all the time until the voltage is too low to actually light it up. I wanted to voltage-drop the 9v through resistors to be close to 5v, so that when the battery voltage started to drop, the voltage that the chip would see would be lower than the reference voltage, causing the output to change. The circuit does not seem to work as I intended. The output can only sink current, so I have an LED wired to 5V, through a 470-ohm resistor then to the output. 9v Battery Status Indicator Circuit: This is a 9v battery status indicator circuit.One of my friend asked me to build this as he wants a 9v transistor radio. Considering the fairly broad transition of Figure 1, it is best suited for 9V batteries, but the Figure 2 circuit can be adapted for other voltages. ![]() ![]() Connect a 440uF capacitor between pins 1 and 6, make sure that the negative lead of the capacitor is connected to pin 1. As indicated in the schematic in fig 5, connect a 0.01uF capacitor between pins 5 and 1. I used a 9V supply and battery snap for my circuit. I use a 5k potentiometer to simulate voltage changes. Connect power and ground to pins 8 and 1 of the 555 timer (red and black wires). Then, the 9v is hooked to a 2.2K resistor, then to ground through a 4.7K resistor, with the "input 1 plus" pin connected in between them. (voltage drop of like 0.1v on the 10 ohm resistor). What I was going to attempt was to have a 5v voltage regulator connected to "input 1 minus", using a voltage divider circuit with a 10-ohm resistor and a 4.7 k, to make the voltage go down by a very small amount. I was going to try and make a low battery voltage indicator using an LM339, and after I figured out the circuit itself I would connect it to an Arduino input, and make my program to give a visible indication of a low battery.
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