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You need a de-bouncing circuit to feed the flip-flop’s clock input. LED does not light up, I’ve done something wrong again haven’t I? Always connect the GND pin. Sign up using Email and Password. I’m a complete amateur, I’ve probably gotten a million things wrong with this already. In this case, a ohm resistor, combined with the LED voltage and the limited high output drive of the flip-flop will give you about 6 or 7 mA LED current when on.

There are exceptions, with some circuits incorporating a built-in pull-up or pull-down resistor, but unless the data sheet mentions these, assume they don’t exist.

As others have suggested, this could be a simple R-C network, or as a better option, use an SPDT change-over switch and a set-reset SR flip-flop as a de-bouncer. And 74c109 think that you can ignore the inputs of an unused part of the circuit, such as the unused flip-flop in your 74HC Home Questions Tags Users Unanswered. WhatRoughBeast 49k 2 28 By using our site, 774hc109 acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.


74HC109 DIP-16 J/K flip-flop

On the one hand, it will try to draw too much current in the on state, and will also clamp the output to a low voltage which the input will not recognize as high. Don’t even think about it.

Sometimes that works, and sometimes it doesn’t. John Honniball 2, 6 9.

74HC Datasheet(PDF) – NXP Semiconductors

Email Required, but never shown. Just pull it down to 0V with a single resistor! Sign up using Facebook. You are clocking a flip-flop directly from a switch that has not been de-bounced.

74HC109 Datasheet PDF

In this case, it will show up as intermittent operation of the flip-flop, depending on whether or not it got an even or odd number of contacts when you press the switch. Post as a guest 74hc09. Post Your Answer Discard By clicking “Post Dataseet Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the datasheef is subject to these policies.

Connect the cap directly to the sockets nearest the IC power and ground pins. Never leave it unconnected, even if the circuit appears to work. Leaving unused pins floating particularly with CMOS can produce amazingly intermittent, bizarre and maddening errors. By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies.


Please build the following circuit: When the circuit is powered, the led turns on but does not toggle when the momentary switch is pressed and released. Sign up or log in Sign up using Google.

digital logic – Unable to toggle SN74HC – Electrical Engineering Stack Exchange

A common way to do this is with cross-connected NAND gates. I’m trying to toggle the led forgot to add a resistor in the diagram, ah, also forgot to add a line from 5V to Vcc.

For more complex circuits using counters or state machines you can get the most amazing errors. Just to show what I’m talking about, once you’ve got the circuit working, put an LED directly to ground on the flip-flop clock datwsheet, and watch what happens. Maximum Low-Level input voltage with my Vcc at 5V is about 1.

I’m using an SN74HC dual j-k” flip-flop chip.

LED lights up but does not toggle. Tie them all high or low.