Copyright © 2004 E-Lab Digital Engineering, Inc. All Rights Reserved. Page 1/5 EDE2008 Pushbutton Debouncer IC Pushbutton Debouncer with Eight Independent ChannelsFeatures:• Debounces up to eight independent momentary pushbuttons• Operates in both directions for active high or active low inputs• Works with mechanical & membrane buttons• Eliminates all contact bounce noise and glitch activity to provide cleansignal to host circuit• Each channel operates independently• 25ms debounce period on both rising and falling edges• TTL/CMOS compatible outputs• Serves to buffer host logic via input clamp diodesDescription:The EDE2008 Pushbutton Debouncer IC provides eight independent debouncing channels for use ininterfacing mechanical pushbuttons to electronic circuits. All mechanical contacts exhibit contact ‘bounce’,interpreted to logic circuits as multiple false signals, when they make or break contact. The EDE2008removes this bounce on both the positive and negative edges of the signal providing a clean output signalfrom the mechanical switch. Applications include pushbutton interfacing to microcontrollers & other logic,turnstile counters, CNC machine limit switches, and user interface buttons.EDE2008/PEDE2008/S00-70 ˚C – Standard TempEDE2008/x-I-40 to +85 ˚C – Industrial TempEDE2008/x-E-40 to +125 ˚C – Extended TempEDE2008 Pushbutton Debouncer IC Page 2/5PIN DEFINITIONSButton Connections:Button In 1 (Pin 1)......................................……………………...mechanical pushbutton input #1Button In 2 (Pin 2)......................................……………………...mechanical pushbutton input #2Button In 3 (Pin 3)......................................……………………... mechanical pushbutton input #3Button In 4 (Pin 4)......................................……………………... mechanical pushbutton input #4Button In 5 (Pin 6)......................................……………………... mechanical pushbutton input #5Button In 6 (Pin 7)......................................……………………... mechanical pushbutton input #6Button In 7 (Pin 8)......................................……………………... mechanical pushbutton input #7Button In 8 (Pin 9)......................................……………………... mechanical pushbutton input #8Debounced Outputs:Output 1 (Pin 18)......................................……………………..... debounced output #1Output 2 (Pin 17)......................................……………………..... debounced output #2Output 3 (Pin 16)......................................……………………..... debounced output #3Output 4 (Pin 15)......................................……………………..... debounced output #4Output 5 (Pin 13)......................................……………………..... debounced output #5Output 6 (Pin 12)......................................……………………..... debounced output #6Output 7 (Pin 11)......................................……………………..... debounced output #7Output 8 (Pin 10)......................................…………………..…... debounced output #8Power:+5V (Pin 14)...............................................................………..….connect to +5V DCGND (Pin 5)....................................................................…..…....connect to 0V DC (Ground)Note: DIP are SOIC (surface mount) packages of the EDE2008 have identical pinout and pincount.Please specify EDE2008/P (DIP) or EDE2008/SO (SOIC) when ordering. Standard temperature range is0 to 70˚C.EDE2008 Pushbutton Debouncer IC Page 3/5Figure One: Single-Channel Debouncing Example(Note: unused inputs (pins 2-4, 6-9) should be tied to ground. Pins left unconnected here for clarity.)As illustrated by Figure One, the EDE2008 connects easily to any momentary pushbutton. In thisexample, the Button Input 1 (pin 1) is pulled to ground through a 4.7K resistor. Pressing the buttonconnects +5V to the input, turning it from low to high. Upon seeing this transition, the EDE2008 waits25ms and samples the input. The 25ms waiting period allows the button’s contacts to settle at their newstate and ensures that contact bounce noise will not be transmitted to the output. The timing diagram inFigure Two illustrates the debouncing of the pushbutton.Figure Two: A Single Button Press and the Corresponding EDE2008 Debounced OutputAs can be seen above, the EDE2008 output lags changes in the corresponding input by 25ms, and alsoprovides noise-free transitions. In the above situation, the EDE2008 output pulse length roughlycorresponds to the input pulse length. If the button were held for a longer period of time, the output pulsewould also be longer.The EDE2008 debounces both the positive and negative edges of the transition. For example, in a circuitthat is normally high that goes low when the button is pressed, the waveforms would look similar to thoseseen in Figure Three. Notice that the functionality is identical to that of Figure Two, with the exception ofthe polarities reversed.ΩΩΩΩmsOutput 1Button In 10 100EDE2008 Pushbutton Debouncer IC Page 4/5Figure Three: An Active-Low Button Output and the Corresponding EDE2008 Debounced OutputIt should be noted that if a button press is shorter in duration that 25ms, the EDE2008 will interpret it asnoise and will not produce a change in its output, as illustrated by Figure Four below. For comparison, astandard button press lasts from 100 to 500 ms.Figure Four: Signals Shorter Than 25ms Will Not Trigger an Output PulseEach of the eight input channels of the EDE2008 may be utilized independently from one another. Activityon one channel in no way affects any of the other channels. Channels may be used as active low oractive high debouncers, in any combination.msOutput 1Button In 10 100Output 1Button In 1ms0 100Important Note: Unused INPUTS of the EDE2008 should be connected toeither +5V (Vcc) or Ground to avoid oscillation and excessive power draw.Connection may be direct or through a resistor, such as 4.7K Ohm. UnusedOUTPUTS should be left unconnected.Copyright © 2004 E-Lab Digital Engineering, Inc. All Rights Reserved. Page
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