Work on 555 Submissions

I've just done this illustration for some theory of operations of the 555. If you see a problem this is the time to tell me.... please.




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Found a problem, edited and corrected.

The pin names are correct but make these changes:

threshold 6 to control voltage 5
control voltage 5 to threshold 6

Check this one here

http://www.uoguelph.ca/~antoon/gadgets/555/555.html

Thanks, fixed. Drawing tired, but then thats why I asked for the check. I was using this one from a data sheet.

Status: Ready to proof read
Illustrations: Complete
Schematic: Verified
Notes:.........9/2/2009 Schematic drawing error found, corrected

This is an experiment using Notepad and LaTex. I'll be editing my 555 Schmitt Trigger submission a little, and this is where I'll be doing it.

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555 Schmitt Trigger



PARTS AND MATERIALS

• One 9V Battery
• Battery Clip (Radio Shack catalog # 270-325)
• Mini Hook Clips (soldered to Battery Clip, Radio Shack catalog # 270-372)
• One Potentiometer, 10 KΩ, 15-Turn (Radio Shack catalog # 271-343)
• One 555 timer IC (Radio Shack catalog # 276-1723)
• One red light-emitting diode (Radio Shack catalog # 276-041 or equivalent)
• One green light-emitting diode (Radio Shack catalog # 276-022 or equivalent)
• Two 1 KΩ Resistors
• One DVM (Digital Volt Meter) or VOM (Volt Ohm Meter)

CROSS-REFERENCES

Lessons In Electric Circuits, Volume 3, chapter 8: Positive Feedback
Lessons In Electric Circuits, Volume 4, chapter 3: Logic Signal Voltage Levels



LEARNING OBJECTIVES

• Learn how a Schmitt Trigger works
• How to use the 555 timer as an Schmitt Trigger

SCHEMATIC DIAGRAM




Schmitt Triggers have a convention to show a gate that is also a Schmitt Trigger, shown below.




The same schematic redrawn to reflect this convention looks something like this:





ILLUSTRATION


INSTRUCTIONS

The 555 timer is probably one of the more versatile "black box" chips. Its 3 resistor voltage divider, 2 comparators, and built in set reset flip flop are wired to form a Schmitt Trigger in this design. It’s interesting to note that the configuration isn’t even close to the op amp configuration shown elsewhere, but the end result is identical.

Try adjusting the potentiometer until the lights flip states, then measure the voltage. Compare this voltage to the power supply voltage. Adjust the potentiometer the other way until the LED’s flip states again, and measure the voltage. How close to the 1/3 and 2/3 marks did you get?

Try substituting the 9V battery with a 6 volt battery, or two 6 volt batteries, and see how close the thresholds are to the 1/3 and 2/3 marks.

Schmitt Triggers are a fundamental circuit with several uses. One is signal processing, they can pull digital data out of some extremely noisy environments. Other big uses will be shown in following projects, such as an extremely simple RC oscillator.


THEORY OF OPERATION

The defining characteristic of any Schmitt Trigger is its hysteresis. In this case it is 1/3 and 2/3 of the power supply voltage, defined by the built in resistor voltage divider on the 555. The built in comparators C1 and C2 compare the input voltage to the references provided by the voltage divider and use the comparison to trip the built in flip flop, which drives the output driver, another nice feature of the 555. The 555 can drive up to 200ma off either side of the power supply rail, the output driver creates a very low conduction path to either side of the power supply connections. The circuit "shorts" each side of the LED circuit, leaving the other side to light up.

The 5KΩ resistors are not very accurate. It is interesting to note that IC fabrication doesn't generally allow precision resistors, but the resistors compared to each other are extremely close in value, which is critical to the circuits operation.

The alternate editing technique may have let me get by with something, or maybe not. I thought there was a limit of 4 pictures in a post.

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After some experimentation I've found out the max pictures is now 6 images, good enough.

Hello Bill,

Do you know the animation at fallstad.com on the NE555.
http://www.falstad.com/circuit/e-555int.html

Greetings,
Bertus

Pretty neat. I'm writing for the AAC ebook, so animations are out, but it is something to keep in mind for the new guys.

I'm also learning more than I ever wanted to learn about LaTex and other script editors.

Right now I have to figure out how to insert line spaces in LaTex. Almost there though.

So anyone know the single line command in LaTeX VB style?

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Figured out what I was doing wrong.

Hello,

What verion of LaTeX are you using?
There is a special LEd LaTeX editor : http://www.latexeditor.org/
There you can find also links to documantation on standard LaTeX.
http://tex.loria.fr/english/general.html

I hope you can find what you need over there.

Greetings,
Bertus

PS I have LaTeX for linux, I must say I have never tried it.

I'm using Windows notepad, which is a basic text editor, and typing the format commands by hand. You can look at it by downloading the attached file on post #4. This is the basic stuff of this forum, and for the actual submission I use SubML (Sub Markup Language). Like I said, I'm getting more familar than I ever wanted. For home use I have Office 97.

Any News? Or would you like more submissions first?

Bill_Marsden said:

Any News? Or would you like more submissions first?

Click to expand...

Bill, as per our PM correspondence, I am happy for Dennis to add this to the e-book. If you could either generate and upload the SubML files or confirm if they are these in this thread.

On a side, Volume III credits has been updated here at AAC: http://www.allaboutcircuits.com/vol_3/chpt_14/2.html

Apologies for the errors.

Dave