555 toggle flip flop?

Thread Starter

k1ng 1337

Joined Sep 11, 2020
85
Good Day,

How can I use a 555 as a T flip flop? It needs to toggle at the rising edge of an input that will be active high for 1 hour then active low for 11 hours

Cheers :)
 

Thread Starter

k1ng 1337

Joined Sep 11, 2020
85
No. You need a 74HC74 or 4013.
What about using a d flip flop? I have a sn74hc574n on hand as well as a bunch of logic CMOS chips.. nand, inverters etc.

I had an extra 4017 to use as a toggle but it got ruined today, maybe I'll just build a jk latch out of discrete components to use em up
 

Ian0

Joined Aug 7, 2020
2,196
You need a D-type flip-flop with a notQ output (such as a 4013 or 74HC74). A 74HC574 is a D-type flip-flop, but has no notQ output.
 

Thread Starter

k1ng 1337

Joined Sep 11, 2020
85
You need a D-type flip-flop with a notQ output (such as a 4013 or 74HC74). A 74HC574 is a D-type flip-flop, but has no notQ output.
I'm going to build a jk out of nor gates, looks like it will take 8 gates on two 74hc02 chips

Any drawbacks to this crude design?
 

Ian0

Joined Aug 7, 2020
2,196
I presume the design you'll use is exactly what is in a 4027 or 74HC73 etc. so I don't see why it shouldn't work.
I could have a JK flipflop in my mailbox tomorrow morning, and it would take me longer than that to wire up 8 nor gates!
Apologies for not being helpful!
 

Thread Starter

k1ng 1337

Joined Sep 11, 2020
85
I presume the design you'll use is exactly what is in a 4027 or 74HC73 etc. so I don't see why it shouldn't work.
I could have a JK flipflop in my mailbox tomorrow morning, and it would take me longer than that to wire up 8 nor gates!
Apologies for not being helpful!
I got it to work but I'm having bouncing problems, I tried a few different ways of pulse detection and even a clean pulse from a 555 in monostable as well as a clock signal (which it lags behind or sometimes not at all) still bounces regardless of the pulse duration, so it seems to be an instability in the nor network somewhere

I doubt you could help without having the schematic, it's a bit of a mess.
 

sghioto

Joined Dec 31, 2017
2,363
How can I use a 555 as a T flip flop? It needs to toggle at the rising edge of an input that will be active high for 1 hour then active low for 11 hours
Sure. When the 555 is triggered what does the output state need to be high or low?
 
Last edited:

djsfantasi

Joined Apr 11, 2010
7,689
OK, so why is the output state off the 555 irrelevant when triggered?
Because the design constraints of the circuit (0.000023Hz at 8.3%) is unrealistic. You won’t be able to use a 555, so it’s output state is irrelevant.

Plus, even if it were, a simple transistor inverter (NOT) would get you what you want.
 

Tonyr1084

Joined Sep 24, 2015
5,969
Something sticking (stuck) in my mind is the time period: Active high for 1 hour, active low for 11. That's quite a long time period. If you want any kind of accuracy then this is not the way to go about it. Just getting a 555 to pulse once every hour is not an easy thing to do. The biggest problem with that is the RC circuitry. Caps leak. Resistors can change value with temperature. Steering diodes, which would be likely are also temperature sensitive and will affect the timing.

[edit] forgot to ask for a diagram of what you're doing. [end edit]
 

sghioto

Joined Dec 31, 2017
2,363
The TS wants to use the 555 as a FF not an oscillator.
It's the trigger pulse that will be high for 1 hour then low for 11 hours is my take.

TS stated "rising edge of an input that will be active high for 1 hour then active low for 11 hours"
 

djsfantasi

Joined Apr 11, 2010
7,689
The TS wants to use the 555 as a FF not an oscillator.
It's the trigger pulse that will be high for 1 hour then low for 11 hours is my take.

TS stated "rising edge of an input that will be active high for 1 hour then active low for 11 hours"
That’s a valid interpretation. Let’s confirm it. I’m not as confident as you that that is what he means.

...Because the duty cycle and frequency is irrrlevant unless they approach the design limits of a flip flop.
 

Tonyr1084

Joined Sep 24, 2015
5,969
The TS wants to use the 555 as a FF not an oscillator.
It's the trigger pulse that will be high for 1 hour then low for 11 hours is my take.

TS stated "rising edge of an input that will be active high for 1 hour then active low for 11 hours"
OK, yes, looks like I overlooked that part of it. That's what happens when I don't pay enough attention.

So, we have a trigger that is high for one hour and low for 11 hours. Would have to sleep on it. What's the source of the timed inputs? I'm interpreting this to be a high signal from (let's assume) 12AM to 1AM then again from 12PM to 1PM.
 
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