555 timer

[BulgingCap]

This week I needed a simple timer for a small project so dug out my drawer of 555s.
I must have used many dozens over the years, especially when I was making production test rigs, but was distressed to find that I had forgotten the pinouts. A quick look on the net and I found the data sheet, but also got snared by a post about how the device got its type number. It was claimed that the 3 x 5s was due to 3 x 5k internal resistors used as a divider. I was a bit sceptical so delved deeper. I found this article which is interesting:
http://www.semiconductormuseum.com/T...zind_Index.htm
A short article about Hans Camenzind who was a chip designer at Signetics in the late 60s. It is most amazing in that the 555 seems to have been an almost solo design effort- certainly the concept was. It was never patented either.
BC

[kalee20]

It's a good IC! Great architecture. And pretty high spec, especially at the time, for input current at the threshold and trigger inputs.

One of its foibles is that there is a design weakness in the output stage - at instant of switching, there is a brief period of shoot-thru current. So it needs a bypass capacitor across the supply pins, close to it.

As well as a timer, I have used it as a Schmitt trigger (just connect the Trig and Thresh pins together and use as input pin). With a stabilised supply rail, the input switching levels are very accurately defined.

Hans Camenzind himself wrote a rather good little book, which I can thoroughly recommend.

[Ed_Dinning]

Hi Peter, a very interesting book, I wounder how many of us still have the original Signetics applications book, completer with cartoons

Ed

[Uncle Bulgaria]

That reminds me of the Wikipedia rabbit hole I went down last night, culminating in the mad story of Bob Widlar and his designs of genius

[Wendymott]

Thanks BC for directing us to such a wonderful insight to the 555.

[short wave]

Doing a bit of http "chopping" produced this....
http://semiconductormuseum.com/Museum_Index.htm
worth a look round

[Argus25]

I discovered something very interesting about 555 timers and I would never have known unless for a particular video circuit that used them, though it was obvious that the external components could be quite different for the cmos versions with lower input currents compared to the bipolar versions, but these are different to each other too.

Atari arcade Pong from 1972 use two NE555N's to generate the player paddle positions, triggered by a vertical pulse and the delay being controlled by a DC level from a player's potentiometer. The delay determines the vertical position of the player's paddle.

Since I built some of these games myself I found out that the original NE555N is in fact unique.

Despite the plethora of 555 clone IC's, NE555V, various cmos versions, the National LM555, they are not in fact exactly the same functionally.

You could interchange them in a few hundred 555 timer circuits and never detect there was any difference.

But this is not the case in the Pong circuit. The exact delay after the trigger pulse is different between the different sub types and the linearity of the way the control voltage sets the delay over the control range is different for every sub type of 555 IC I have tried in this circuit, except that is for the NE555N they are all uniform/identical, at least vintage old stock ones from the 1970's and 80's, not re-labelled ones. So I had to acquire genuine NOS NE555N's.

However every other sub type of 555 malfunctions in the circuit with the control range properties being unsatisfactory.

[KeithsTV]

Originally Posted by Ed_Dinning

Hi Peter, a very interesting book, I wounder how many of us still have the original Signetics applications book, completer with cartoons

Ed

I do

Here's the cover plus a couple of the cartoon pages.

Keith

[emeritus]

I remember using the 555 timer when it first came out. It rendered obsolete the "Multivibrators" module I had studied at college! A project I was working on at Plessey required a test jig to switch a circuit on and off for specified durations, 50 times. I had been allocated a week for design and construction. I used two 555 timers, one to give the specified mark-space ratio, the other configured as a one-shot with an ON time equal to 50 of the On-Off periods that energised the first 555. Design took about 5 mins, construction 15, and it worked like a dream.

[McMurdo]

I still use them alot in commercial projects where it doesn't warrant anything more sophisticated.

The rather fetching piece of pottery below is transfer-printed on machines using stepper motor controls I designed with the clock frequency generated by 555 timers.

[Terry_VK5TM]

For those that would like to see the full version of the 555 book mentioned above, it is available here in various formats.

https://archive.org/details/Signetics555556Timers

[kalee20]

Irrespective of his ability to design an IC that worked, there is the astonishing imagination that Hans Camenzind displayed, thinking of a black box, its inputs and outputs, foreseeing what the world would want.

I've only used the 'reset' pin once myself... but everything is just so 'right'. Nobody has come up with a new timer chip containing another function pin not available in the 555. It's brilliant!

Originally Posted by emeritus

I had been allocated a week for design and construction... Design took about 5 mins, construction 15, and it worked like a dream.

So what happened to the other 39 hours 40 minutes? It's probably safe to spill now! I'll bet you kept quiet, worked on a homer for the rest of the day and the next 3, then showed your boss your working unit, saying you finished the job a day early and how about a pay rise?

[duncanlowe]

Ah the 555. Did an A level physics project about them, as you couldn't simply look up characteristics on the internet back then. Also made an intermittent wiper module for my first car, but it didn't last too long before that particular IC erupted in flames.

And then just a couple of years ago, my Nephew was doing some work from school, and they were also studying 555s.

You have to be careful though. Some years ago one was being used to initiate a test where large motors were also involved. Somehow as the motors were started up, the 555 initiated the test too early, so one little 555 cost about £1million (or at least the lack of immunity did).

[emeritus]

AFAIR I realised I could use a 555 to build a time lapse unit for my (mechanical ) cine camera, with an array of switches to select 1,2,4,8, 16 etc. seconds between frames in any combination , the unit delivering pulses to a solenoid connected to a cable release. It did work, but the 12V solenoid needed to be driven with a brief pulse of about 36V (stored on a large electrolytic) to give enough force to operate the rather stiff shutter release of my Russian 8mm camera. It went in a large Eddystone box, most of which was occupied by 24 U2 batteries and the capacitor.

No chance of a pay rise, other than by changing employer, that was the era of power cuts, the 3 day week and legally-enforced pay freezes.

[KeithsTV]

Originally Posted by Terry_VK5TM

For those that would like to see the full version of the 555 book mentioned above, it is available here in various formats.

https://archive.org/details/Signetics555556Timers

Saves me from offering to scan the booklet

I've used 555s in monostable mode in a couple of electronic ignition circuits, both of which have been published. One was used to trigger the SCR for a CDI system with the output also being used to drive a meter as a tachometer. I used the reset input to inhibit the 555 thus providing a simple anti theft function.

I've also used them as comparators in a control system for a wind generator to switch between wind or mains power.

I obtained a couple of 556s when they were introduced and soon discovered a decoupling capacitor on the supply was essential as the output switching on one timer was capable of triggering the other timer.

Keith

[Ed_Dinning]

Hi Folks, I used 3 of these devices in a safety critical aircraft de-icing system.
Plenty of decoupling and screening and it sailed through the DO-160 certification tests.
It may, in theory have been much simpler to use a micro, but then you need to use certified code and testing, so the time to market is extensive and the costs also rise
(Remember what software did for the 737 MAX!)
It also holds with the KISS principal

As mentioned earlier it is possible to re-trigger the timer with poor decoupling, in fact I believe there was a PW circuit that relied on it for its operation many years back.

Note that some of the other timer families, when used in sequence timers Cmos 4541 ? rely on no decoupling to work.

I've used both the reset pin and the modulation pin on a twin timer unit to give a multi vibrator that has both variable pulse width and frequency, use on an SCR variable speed drive.

Definitely a classic chip

Ed

[G6Tanuki]

The stored-charge issue with the output stage of 555-style chips could be problematic - in times-past some people-of-my-acquaintance used a 556 [which was two 555s in a single-chip package] to debounce the two channels of a rotary servo-shaft-encoder - where you needed to reliably know from the phasing of the transitions whether the shaft was rotating widdershins or deosil.

At high rotational speed - generating pulses up to 50KHz - it was possible for both outputs of the 556 to appear "high" or "low" at the same time - leading to a 'software panic - this cannot be happening' in the downstream circuitry.

[Argus25]

For those interested I have attached the circuit fragment which demonstrated that the Signetics NE555N is unique.

The delay until the output changes state starts after the vertical pulse and is also controlled by the DC control voltage from the pot and is also affected by the diode's forward voltage drop. The timing of not only the start of the output signal after triggering, but the relation of the rotary angle of the pot to the total delay is unique in this circuit for the Signetics NE555N, as noted, there is no other 555 version I have tried that works correctly in this particular circuit.

So it is interesting the subtle variations in the internal IC design between manufacturers that might or might not have an effect, depending on the design/application of the the IC. For the most part we are used to being able to substitute different manufacturer parts of the same type number and get the same results, but not always.

[TowerRadio]

ETI mag Jan 1977 Vol 6 no1 "38 555 cicuits " R M Marston. Les

[kalee20]

Originally Posted by Argus25

For those interested I have attached the circuit fragment which demonstrated that the Signetics NE555N is unique.

Interesting!

However, I would also suggest that this is a 'bad design,' as it relies on an unspecified aspect of the component. Another batch of devices, which didn't work in the circuit, would be difficult to reject to the manufacturers as they would still be to the published spec.

It could of course be the case, that the designers negotiated with Signetics to assure supplies of devices for this particular mask set, for the production life of their product, or otherwise tied it down. Manufacturers are generally interested in 'specials' if volume is high enough. I'd be interested to know!