18 February 2010

Low-battery indicator circuit

I designed this little circuit to show a battery’s status.

It lights an led to show the battery is OK, and will change to show another colour when the battery’s low.

The transistors can be any npn-type, and the leds can be any colour (in the diagram, green=ok, red=low)

The operating voltage range is ~3v-12v, and by adjusting the resistor values it will work beyond that.

The voltage the low led comes on at, is set by the potentiometer.

12 February 2010

Momentary latching circuit

Here is a little circuit I made that will allow a momentary switch to turn on/off a load.

Q1 can be any NPN transistor, and Q2 is any N-channel MOSFET capable of handling the current being switched. It should be fine with a range of ~5-12V but I've only tested it at 7.4V.

It somewhat mimics the action of a newer console's power button. I made it so I could switch a relatively large amount of power with a small tactile switch, press for on, press again for off.