EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: Guitar760 on August 13, 2015, 11:32:00 pm
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I'm feeding the clock input of a D-Type Positive edge triggered flip flop with a momentary switch on a 5v rail, using 100k ohm for debounce. For the most part, the flip flop won't change states - every now and then it will actually switch but for the most part, nothing.
I hooked it up to my DSO and measured my rise time to be 700 microseconds, so I'm thinkinging it's just too slow for the flip flip to register as a clock input.
Is there a way to speed up the rise time, maybe with a transistor fed from the switch? I'm very limited on space, working a 15mmx18mm board
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Add a Schmidt trigger (e.g. 74HC1G14) in front.
What do you mean "100k debounce"? A resistor alone does not provide this function. Typically a switch or pushbutton is debounced by placing a large capacitor in parallel with the switch (0.1uF is typical), and using a large pull-down resistor (like 100k) so the voltage takes a long time (~10ms) to return to zero after the last contact bounce occurred.
Tim
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If you can replace the IC then you could substitute a D-type variant with built-in Schmitt triggers, such as:
http://www.farnell.com/datasheets/1724714.pdf (http://www.farnell.com/datasheets/1724714.pdf)