Simplest On-Off battery indicator using two LEDs

If you want to teach kids to learn simple LED circuit. This is one of good circuit. It is the Simplest On-Off battery indicator using two LEDs. Both LEDs will show you.

When you turn on S1 to “ON” the current flows to the circuit. While LED1 will briefly flash. But LED2 goes out.

led-display-for-on-off-battery-indicator

Then, we turn off S1 to “OFF” to do not use the circuit. See LED1 still goes out. But LED2 will briefly flash after that it goes out, too.

Why is that?

The 1000uF C1-Capacitor is the hero.

In the circuit, there is the SPDT switch-S1.


If we turn on, the current flow through R1 to LED1, it briefly flashes as C1 begin to charge. Until C1 is fully charging, LED1 will go out.

Since LED1 gets a reverse biased. So it is nothing happens for LED1.

Now, C1 has the current full and there is less Leakage current.

Then, we turn off, NO the current to the output. But not end, the current in C1 discharges to LED2. It also briefly flashes. Unit the current in C1 is empty. LED2 goes out.

For LED1 goes out because it gets reverse polarity.

See look like of both LED display in video below:

‘4 LED voltage indicator circuits’ »

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