High Impedance Inputs

[Mikebits]

how can a 555 be called a precision timer

Good call, never thought about that one.

 

[spec]

Good call, never thought about that one.

I expect to get some flak about that comment.

spec

 

[Mikebits]

I expect to get some flak about that comment.

spec

Would not be fun otherwise

 

[Mikebits]

I am sorry for not being more specific. I was talking about the noises in my head!
Also I noticed OP used a Tin Mint for his project box. Don't you think that would contribute to the noise and if a plastic chocolate box was utilized, it would have been a more suitable medium?!
EG

Edit: I like chocolates

Why not ask me? When connected to the scope, the case is connected to ground side of scope so with case closed resistor is shielded on center conductor side. When connected to my DMM, I connected the case to chassis ground through a 1uF cap, thus acting as an EMI shield. I took this method from a Fluke App note I once came across.

 

[spec]

at my last job we were forbidden from using the part (At the time, did not know why only it was off-limits).

I wounder why the ban. I know that there was a few problems with some of the early 555s- unstable timing and huge current glitches on the supply lines as both the output halves turned on at the same time during switching edges, but I think later 555s don't have these problems to the same degree. Also, not all 555s are the same- it depends on manufacturer.

I tend to prefer the MOS versions of the 555: LMC555 and TLC555, but they do not have the same 200mA output current capability of the standard bipolar 555.

spec

 

[spec]

Would not be fun otherwise

Yes, that is true.

spec

 

[dr pepper]

A shield wouldnt do a fat lot if it wasnt grounded.
You mentioned who has such as thing with high input impedance and high gain, my Vlf antenna is just such a thing, mains hum is a real problem, so's mounting it in a tin box.

 

[Mikebits]

A shield wouldnt do a fat lot if it wasnt grounded.
You mentioned who has such as thing with high input impedance and high gain, my Vlf antenna is just such a thing, mains hum is a real problem, so's mounting it in a tin box.

When connected to the DMM the shield has a low impedance AC ground through the cap. This is not a DC ground however so some low frequency component is unaffected.

When connect to the scope, the shield is connected directly to ground, I thought I mentioned that?
This was just an experiment in test and measurement.

 

[dr pepper]

Yes you might have mentioned it, my old age is making me not listen.

 

[schmitt trigger]

In defense of the 555, one has to remember the time period where it was designed....... it is the bronze age of monolithic devices, simple and crude. But its very simplicity has allowed it to thrive and survive while many other ICs have long vanished.

Disclaimer: I'm a little biased towards the 555.
The very first project employing ICs that I built that actually worked was a 555 blinking a LED. I then replaced the LED with a speaker and made a simple tone. Added a pot and the tone would change at will.
That little project helped settle my decision to pursue a career in Electronics.

 

[KeepItSimpleStupid]

The 555 sucks as a one shot and what it does on power up is anybodies guess. Try making a one shot on power up or try to not make it do that.

 

[dr pepper]

I stand by the venerable 555, it has been argued as the most successful component.

 

[audioguru]

I recently started using Cmos 555 ICs as the oscillator in LED blinkers I have been making lately using discarded strings of LEDs from Christmas tree lights that failed. The last one I made had two groups of blue LEDs alternately fading back and forth. Then I added two Cmos Schmitt Trigger gates as a frequency doubler so that as each side fades to zero then a group of very bright red LEDs flash.

I realized now that one of the two unused gates could have been the oscillator. Maybe I will think of something else they can do.