posted by Lee Hart, March 1 2010, in the cosmacelf Yahoo group. This is a response to a thread "Re: Membership Card - Ultra Low Power Variant". It's based on a smaller version of his 1802 Membership card. see the memship.html Web page for details. The "files" section has a "membership card" folder with "LCD.PDF" for this varient design. - Herb Johnson NOte: The 4503 is a non-inverting buffer IC, with the output enable always set active. There is a 10K resistor from input to output, and the toggle switch drives the input either to ground or to power. IN the "membership card", Lee uses a two-input OR gate for similar effect. - -herb Lee posts: The switches *are* debounced. See the feedback resistors (R6, R14, R15) around the buffers (U9E, U8E, U8F)? The switches (S1, S2, and S4) are SPDT. When you move them from one position to the other, say, from the NO (normally closed) to the NO (normally open) contact, the sequence of events is: NC contact closed NC contact bouncing open/closed no connection from common to either NC or NO NO contact bouncing open/closed NO contact closed The 4503 buffer starts off with its input held low by the NC contact. It's non-inverting, so the output is also low. The input and output voltages are the same, so there is zero current in the resistor. Now you move the switch. When the NC contact starts bouncing open/closed, the resistor holds the input low regardless of the switch bounce. Power supply current is still zero. When neither NC nor NO contacts are closed, the resistor still holds the 4503 output in its last state, still at zero power. When the NO contact first touches, it forces the 4503 input high in spite of the resistor. There is a momentary pulse of current in the resistor, for the time it takes the 4503 output to go high. Then the current is zero again. While the NO contact is bouncing, the resistor holds the 4503 input and output both high, at zero supply current. Thus, this circuit debounces the switches, and takes (essentially) zero power to do it. This particular design was optimized for minimum power consumption. - Lee Hart text copied by Herb Johnson 2/12/2010.