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pulse genetator

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bigheadted

Electrical
Jul 22, 2005
53
i am looking for a device that will generates 24v pulses of duration 5ms at a frequency of around 0.8HZ can anyone help i have looked at some of the small modular plcs but the timers are not short enough
if the duration and frequency could be linked to a pot all the better
thanks
rich
 
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I just have too many bad memories of 555 circuits. Switching regulator ICs like SG3524 or TL494 can do this entire function with one chip and very few components. One pot could change the rep rate and a second pot would do 0-50% duty cycle. They don't give specs for these at such a low frequency, but I have seen them used in marine labs as wave generators at more than 20 times slower than you want. Output could source or sink up to about 36V at decent current. Parts count would be half that of a 555 circuit. If it is just one of, good pulse generators are pretty common for under $50 including shipping on eBay.
 
The ubiquitous 555 has one nasty property that upsets many circuits. At the instant of switching the totem-pole output transistors are both momentarily on, drawing about 1A for a microsec or so and this causes power supply glitches that are difficult to filter. The CMOS version 7555 does not have this problem.
 
I too raise my hand to say 555's suck.
I have used them maybe 20 times. I think the average is they take 4 times longer to get working the way you want them then you'd ever expect. And about 1 out of 4 times you flat can't get them to do the job.

On the brighter side they have newer ones that don't short the totempole and sink 20 times more than the original. Go for the CMOS versions. Look to Intersil. Ah yes, now I see BrianR has already pointed out this nifty fact...
 
I think you guys suck. Running old junk-box parts when there are new ones without problems.

Everyone knows about the problems with bipolar 555s - and we have known about that for at least thirty years. So why keep on moaning about it? It is the 21st centuty after all...

This is a good application for a 555 - and I do not say CMOS - that is kind of understood.

Gunnar Englund
 
I'll add a vote for the TL494/594's and SG38xx's...
Seems that every proto I have built with one of these types
has worked first time, every time. Can't say that for the
555's - built a LOT of them that needed patching to be
stable of buffered (and a lot of them that worked right
off the bat ).
That being said, I think any RC-based timer needs a divider
if one goes much over a 500 mSec period.

There are some examples using all the above types from
40 nSecs to hours at:
<als>
 
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