Drive Multiple LEDs by Using Only One NiMH Cell

Description:

This simple circuit allows us to drive serially connected seven LEDs by using a single NiMH (Nickel Metal Hydride) AA cell. As you can see there are a few components, a CMOS 555 timer, an NPN transistor, an inductor, three resistors and two capacitors.

The circuit produces voltage pulses at a much higher level than the input supply voltage by pulsing the 220 uH inductor. The inductor must be a high Q (Q>90) power inductor. When the input is 1.25 V and the LEDs are connected, the voltage pulse level will be 23V.

Since the circuit operates with low supply inputs (as low as 1V), it uses a CMOS timer. When a single cell rated at 2000 mAh is connected , the circuit works for about 190 hours. The 555 timer drives the transistor at 222 kHz rate. The circuit is also can be used as a high power LED driver. Obviously, the greater the mCd rating, the brighter the LED will appear.

The seven LED groups can be connected paralelly if their forward voltages match. If not, the LED group with the lowest forward voltage value will dim out the other group(s). This parallel connection will not effect the total current drawn from the battery but it will reduce the brightness of the LEDs.  So the total operating time will not differ.

When a single 1.25V cell is used, the seven LED group will draw about 8mA from the battery. When the input value increases to 2.5V, the total drawn current will be 20mA and the LEDs will be so brilliant that it is difficult to look at them.

Switch Debouncer with Only One Inverter

Description:

This circuit acts as a debouncer that prevents multiple logic signal transmitting when a switch is pressed. It takes its logic power from only the remote pull-up resistor R2 and can be used in non-energized devices such as a device in a system that's just coming from the stand-by.

The Circuit Operation:

When the S1 button is at the release position, C1 capacitor is charged and keeps the inverter (7z04 - Ultra High Speed Inverter) input at a high state so the output of the inverter is low. Since the inverter output is already connected to the ground, it draws no current - consumes no power. In this situation, the output Vout keeps its state at high. 

When the S1 button is pressed, C1 discharges and the state of the input of the inverter changes to low so the output of the inverter goes high and the IC starts to conduct heavily. As a result, Vout becomes low until R1 charges C1 to drive IC again towards Vss. When the capacitor charges sufficiently enough, IC stops driving current and Vout returns to a high state.

D1, D2 and D3 diodes are in conjunction with R3 to shift the level of Vout for improved compatibility with CMOS gate.