Parameters for using 555 Timer

[Cincinnati10]

Q1: — What is the frequency range I can get out of a 555 timer?

Q2: — Can I use a 555 with a positive ground system? IE: will it work as long as V at pin 1 is lower than V at pin 8? (If I connect pin 8 at 0 VDC and pin 1 at -12 VDC, will the waveform output be a negative voltage instead of a positive voltage output when I connected pin 8 to +12 VDC and pin 1 to ground?)

 

[IRstuff]

Q3. Why haven't you looked at the datasheet?

TTFN

FAQ731-376

 

[felixc]

There's the datasheet to know better about its capabilities.

http://www.national.com/JS/searchDocument.do?textfield=lm555c

To operate it with the positive being the ground, you have to remember that all the waveforms are documented for the ground pin of the chip being the reference. This is especially important if you want to to control it through its inputs. Any noise on your negative supply may be interpreted as noise on these inputs if they are driven from a source that has its reference at the ground.

 

[VEBill]

There is (was?) a CMOS variation of the 555 with significantly different specs.

 

[geekEE]

TI still has their CMOS version:

http://focus.ti.com/docs/prod/folders/print/tlc555.html

The 555 refuses to die, even though most everyone on eng-tips says, "Yech! There are better ways of doing the same thing in almost all cases."

 

[itsmoked]

"significantly [blue]better[/blue] specs"

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[VEBill]

"better"

The CMOS version is un-better in terms of sourcing, and especially sinking, current. My gut knew that there was something un-better about the CMOS version, but I had to look it up (just now).

 

[VEBill]

Uh sorry, vice versa on sink and source. CMOS sink 100mA, source only 10mA.

Normal 555 is 200mA either way.

 

[itsmoked]

Really! I'll take yur word for it.

I remember being directed to the CMOS version once because it sank more current than the 'plain' one. I think I was mis-guided.



I found the original Signetics Data Sheet,(I worked there after all), and even it stated 200mA. Maybe the discharge pin?? As it's not even categorized in the SE555.

Anywho, thanks for the correction.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

The bipolar was a current gulper. The CMOS is better in that way.

Keith. You worked with Signetics? They produced the aesthetically most pleasant data books ever. Keep two of them. Dated 1974.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

Yes I did,(straight outta school). Was one of three EEs developing an advanced mechanization system. We took the tested wafers sawed them up, placed them on the lead frame, wire bonded them, molded a single lead frame, punched out and bend the lead frame and separated the ICs without a human touching anything. Used a CP/M based computer. Designed and hand made 8048 SBCs and Z80s. Hand coded them in HEX. Hacked commercial saw keyboards so we could press the buttons with the SBCs. Reed relays galore.

It was a blast. Got it all working before it was expected. They fired our boss and reassigned us to a dork. We all quit the same day.

Yes they did produce nice Data Books on bright white very thin paper.

I probably only have the first one with the 555 application notes in it. 8-1/2 x 11 red and white cover. Kept it because it had the clearest descriptions I ever saw for the 555.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[bogeyman]

The bipolar 555 has a nasty switching characteristic it puts both the sink and source on for a few nano seconds when the output changes state this draws a horrid hefty and fast edged pulse(>500mA)from the supply which will invariably drop in response to the pulse, it is essential that very good decoupling is employed with this fast spike.
The thing can drive a relay directly but only if a forward diode is connected between the output and relay as well as the usual commutating diode, without it the device will tend to self trigger on switch off.
The CMOS version does not suffer these drawbacks.
Other than that its a very handy and simple little device and its no surprise that it still gets used in considerable quantities, even where it shouldn't.

 

[richs]

Off topic-

Keith. Remember Signetics Memory Systems (SMS)? We built
the 8X300 micros. That was my first real job out of school!
Sunnyvale based company, spun off from the big S, went
public and I think it went bust about mid 80's or so.
Wire bonded cpu's and I/O chips on a ceramic header as
well as other "innovations".

We too had a blast there. Everybody worked. We got into
floppy disk controllers. Even the VP of engineering there
got into the act. He was the best with digital phase lock
loops, so it was his head that was stuck in a scope hood
in the lab.

Yes, the Signetics data books were the nicest. Unfortunately,
I don't have much need for 8T32's anymore, but still keep
my '74 versions of the TI databook. Nowadays though, thank
God for the internet! Data sheets galore!

Cheers,

Rich S.

 

[OperaHouse]

I remember the 8X300. We built a processor in 81 in which nine of them were stacked if I remember right.

Back to the 555. As much as I hate them a novel application is a voltage monitor with separate set points for on and off.

 

[itsmoked]

Yep the 8X300.

Actually we could get 68000s too. I think we second sourced them.

I still have a few. Gawd they were huge!! Like two handed DIPs.

We had a large surplus room full of equipment. At lunch we could peruse it. You could pick up full chassis computers based on 8x300s for $20. I bought a bunch of shiny stuff..

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[GonzaloEE]

I also noticed the voltage peaks bogeyman mentioned. A buffer transistor would be OK between the pin and load.

I thought the 555 was a hero of the last century. There are plenty of better timer ICs today.

Good luck with it, anyway!
Gonzalo

 

[Cincinnati10]

"... I thought the 555 was a hero of the last century. There are plenty of better timer ICs today. "

"What are the "better timers"?

 

[GonzaloEE]

I mean there are lots of timer-ICs, better than the 555.

 

[Cincinnati10]

"... I mean there are lots of timer-ICs, better than the 555"

Sorry. I mean, "What are the better timer IC's?" What would you use/recommend over the 555?

 

[MikeHalloran]

For a mechanical engineer, presumably intimidated by software and complicated electronics, the 555 is a really good choice.



Mike Halloran
Pembroke Pines, FL, USA