555 as flip-flop - flipping and flopping from single input 'low' signal

Hello all,

I had wanted to set the 555 up as a flip-flop, to act on a low voltage signal from an IR receiver.

This worked out ok, in as much as the 555 part is concerned - it dutifully accepts the signal on its RESET and TRIGGER pins and flips and flops to my heart's content.

But silly me hadn't thought it through, if at all, and so as I hooked up the two 555 input pins to the same single pin on the receiver, when the receiver takes and infrared hit it sends a low voltage signal out on both 555 input pin lines and thus the 555 first flips - and flops right back again. Like this - http://upload.wikimedia.org/wikipedia/commons/7/78/555_Bistable.svg - with the RESET and TRIGGER pins bound to the same input signal... Not my proudest moment!

What I was aiming for is some kind of way to have the single IR receiver low-signal make the 555 flip if it's been previously flopped & flop it's been previously flipped...

Can a helpful soul point me in the right direction? Hopefully one that won't require any use of a microcontroller... Maybe there's a good and proper IC that'll do this for me,in which case I'll be very happy to learn about it. Maybe it's all basic electronics, of which my knowledge is still in learning by tutorials-mode. It needs to be a stable solution, though - can't rely on capacitors to flip or flop on a timer-basis.

Many thanks in advance!

A 555 is not a flip-flop. It's an oscillator (multivibrator) or a mono-stable multivibrator.

Yes, there are flip-flop chips. A flip-flop is the simplest kind of memory, with two stable states (high & low). There are several different types of flip-flop circuits. If I understand correctly, you want a Type-T (toggle) Flip-Flop. This output-state changes every time it sees a falling (or rising) clock-edge. I'm not sure if you can a type-T chip, but a type J-K flip-flop can be configured to toggle.

You need a "clean" clock edge. With an IR transmitter/receiver, you may get several edges ("bounce") every time you press the button, or if you move the transmitter. In that case, the 555 in monostable mode, may help to slow-down and clean-up the clock-edge for better reliability.

Hello DVDdoug,

many thanks for your response,

DVDdoug: Yes, there are flip-flop chips. A flip-flop is the simplest kind of memory, with two stable states (high & low). There are several different types of flip-flop circuits. If I understand correctly, you want a Type-T (toggle) Flip-Flop. This output-state changes every time it sees a falling (or rising) clock-edge. I'm not sure if you can a type-T chip, but a type J-K flip-flop can be configured to toggle.

You are correct in that I wish to toggle the output on/off. My IR receiver of choice maintains a 5v high, and upon receving a signal it sends a 0v low - or a series of 5v-to-0v, if the IR transmitter button is held down - through to the 555. Having sent the low-signal, it immediately returns to its 5v high state.

I'm sorry but there's a missing word or two in your last sentence that hints at information I'd be much the wiser for knowing... :-) What's that you're not sure I could do with a type T chip...? "Toggle"? Thanks in advance!

DVDdoug: You need a "clean" clock edge. With an IR transmitter/receiver, you may get several edges ("bounce") every time you press the button, or if you move the transmitter. In that case, the 555 in monostable mode, may help to slow-down and clean-up the clock-edge for better reliability.

Good of you to add the above.

The 555 actually contains a flipflop, but it’s a “set/reset” flipflop, and i don’t think you can get it to “toggle.”

take a look at the 4013:

http://ernstsite.wordpress.com/2-2/

Err, you need a flip flop ? you need a latch a "D" type i think with the inverted output connected to the input (D) and then you make it flip or flop by sending an impulse to the CLK pin, basically the latch will transfer the data on the D pin to the output pin each time it see's a rising or falling clock edge (can be one type or the other) so by connecting the negated output to the D pin you are always supplying as an input the oposite to what is currently on the output so it will flip and flop each time you "clock" it.

74hc221 is a nifty chip. It is a non-retriggerable monostable multivibrator with reset. This means that it can take multiple triggers and make one long, consistent timing pulse out of it. This can be used to debounce a switch or clean up an analog signal that is used to trigger say an interrupt pin on a micro. The timing (pulse length) is set by a resistor and capacitor and can be anywhere from microseconds to minutes in length. The nice thing is that the timing starts with the first trigger edge and it ignores subsequent triggers during the timing event. It also has a reset input to cancel the current timing event. You might find this device handy, or not.

Erni: take a look at the 4013:

Hellow fellow dane,

think you hit the nail right on the head there - seems like just the ticket, the 4013.

Thanks!

sparkylabs: rising or falling clock edge (can be one type or the other) so by connecting the negated output to the D pin you are always supplying as an input the oposite to what is currently on the output so it will flip and flop each time you "clock" it.

Hello sparkylabs,

I'm grasping I should connect d to negated q on a 4013 and that'd do the trick, then? Thanks for guiding me in the right direction!

afremont: 74hc221 is a nifty chip. It is a non-retriggerable monostable multivibrator with reset. This means that it can take multiple triggers and make one long, consistent timing pulse out of it.

Oooo - that sounds very handy as well... Too bad it's twice the price as a 4013 (though in quantities they're approx similar). I had no idea there was such a thing as a 'non-retriggerable' flip-flop - thanks for pointing that out!

harleydk:

sparkylabs: rising or falling clock edge (can be one type or the other) so by connecting the negated output to the D pin you are always supplying as an input the oposite to what is currently on the output so it will flip and flop each time you "clock" it.

Hello sparkylabs,

I'm grasping I should connect d to negated q on a 4013 and that'd do the trick, then? Thanks for guiding me in the right direction!

It's creative use of standard parts but a well used idea, you might even be able to get chips prewired to do that. There are loads of different type of latches, you can do it with other types too by wiring them differently

harleydk:

afremont: 74hc221 is a nifty chip. It is a non-retriggerable monostable multivibrator with reset. This means that it can take multiple triggers and make one long, consistent timing pulse out of it.

Oooo - that sounds very handy as well... Too bad it's twice the price as a 4013 (though in quantities they're approx similar). I had no idea there was such a thing as a 'non-retriggerable' flip-flop - thanks for pointing that out!

It's not really a flip-flop, it's more of a timer since it is monostable (it returns to its initial state after the timer event ends). It's just really handy for say, triggering on an initial trigger that has substantial trailing artifacts that wanted to retrigger my microcontroller.

I had a project that was listening thru a sound sensor for sounds that occurred at regular intervals (clock ticks) so that it could precisely time their spacing. Clock and watch ticks are filled with trailing noises that would retrigger the micro before the next tick occurred. Plus environmental noise added to the problem of false triggers. I needed it to wait until the approximate time that I would be receiving another trigger event before it was allowed to retrigger while ignoring random sounds in between. I tried all kinds of solutions with RC on the comparator output, but nothing really worked well. This chip was a godsend as I could create a blanking window for most of the time period between ticks and it was easy to adjust for different situations. In my case it is clocks with differing amounts of time between the tick sounds. No matter how much noise occurs after the initial trigger, it is ignored and the timing event ends when it should. Most timing chips like this will restart the timing event on another trigger. The 555 comes to mind.

afremont: In my case it is clocks with differing amounts of time between the tick sounds. No matter how much noise occurs after the initial trigger, it is ignored and the timing event ends when it should. Most timing chips like this will restart the timing event on another trigger. The 555 comes to mind.

Good Info - will keep that handy if the need arises, good of you to include that real-world example - thanks.