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A new lesson was posted today:
http://www.pyroelectro.com/edu/basics/555_timer/

Post your homework answers here to compare with everyone else!

1.

What are two uses of the 555 timer?

Metronome, stable timer for time critical circuit

2.

How many pins does a standard LM555 timer IC have and what are the names of each pin?

8 pins in total: (details given for astable mode, which was what was shown in the tutorial)

1) Ground - Most negative potential of the IC
2) Trigger - Connected to Threshold (pin 6) and between R2 and the capacitor
3) Output - Outputs a High (5-15v) or Low (0v) digital signal (square wave) depending on the timing set in the IC
4) Reset - Voltage (0.1-0.4V) applied to this pin resets the output to Low and restarts on-off cycle. Tied to Vcc when not in use.
5) Control Voltage - Used to vary the timing of the device independently of the RC values.
6) Threshold - When given a voltage above 2/3 of Vcc (the normal voltage of the Control Voltage pin), it resets the cycle and sets output to Low just like the Reset pin.
7) Discharge - Connects timing circuit to ground.
Vcc (+) - Input voltage

3.

What R1/R2/C1 values could be used for a 10 milliseconds On-Time pulse from an a-stable
555 timer configuration? (use Frequency = 100 Hz)

I got a strange answer for this -- probably completely wrong.

F = 100Hz = 1/period = 1 /(Ton + Toff)
Ton = 0.01s
100Hz = 1/(0.01s + Toff) => Toff = 0s

Ton = 0.693 * (R1 + R2) * C1 = 0.01
Toff = 0.693 * R2 * C1 = 0
and Ton != 0, so the only component of Ton that can be 0 and is also in Toff's equation is R2. Therefore R2= 0.

0.01/0.693 = R1 * C1

R1 and C1 are factors which multiply to give 0.01443001

coresnake wrote:....
....
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3.

What R1/R2/C1 values could be used for a 10 milliseconds On-Time pulse from an a-stable
555 timer configuration? (use Frequency = 100 Hz)

I got a strange answer for this -- probably completely wrong.

F = 100Hz = 1/period = 1 /(Ton + Toff)
Ton = 0.01s
100Hz = 1/(0.01s + Toff) => Toff = 0s

Ton = 0.693 * (R1 + R2) * C1 = 0.01
Toff = 0.693 * R2 * C1 = 0
and Ton != 0, so the only component of Ton that can be 0 and is also in Toff's equation is R2. Therefore R2= 0.

0.01/0.693 = R1 * C1

R1 and C1 are factors which multiply to give 0.01443001

Hi Coresnake,

Good answers, I like that you looked in detail to what each pin of the 555 timer actually does. Like the 741 op amp there are more complexities in these integrated circuits then I let onto since we're introducing them.

Question #3 was a trick question. You can't have a Ton = 10mS with frequency @ 100 Hz because the period would be 10mS, thus the signal is 'always on'..sorry for making you the test student on this one. I realize now that it's a bit mean. I went ahead and changed the question as I feel students will benefit more from solveable homeworks:

What R1/R2/C1 values could be used for a 10 milliseconds On-Time pulse from an a-stable 555 timer configuration? (use Frequency = 5 Hz, 20 Hz and 50 Hz for 3 sets of R1/R2/C1 Vaues)

Don't be mad at me!

Haha, you got me!

Well technically I solved it right though, since I calculated Toff as 0!

That was a good learning experience nonetheless

HOMEWORK QUESTION 1
What are two uses of the 555 timer?
Proximity alarm and music keyboard
HOMEWORK QUESTION 2
How many pins does a standard LM555 timer IC have and what are the names of each pin?
eight!
1=Ground, 2=trigger, 3= output, 4=reset, 5=control Voltage, 6= Threshold, 7=discharge, 8= Vcc (+)
HOMEWORK QUESTION 3
What R1/R2/C1 values could be used for a 10 milliseconds On-Time pulse from an a-stable 555 timer configuration? (use Frequency = 5 Hz, 20 Hz and 50 Hz for 3 sets of R1/R2/C1 Vaues)


HOMEWORK QUESTION 4
If a 555 timer’s output signal has a period of 25 milliseconds, what is the frequency of this signal?
f=1/0,025=1600Hz

jonnyquin wrote:HOMEWORK QUESTION 1
What are two uses of the 555 timer?
Proximity alarm and music keyboard
HOMEWORK QUESTION 2
How many pins does a standard LM555 timer IC have and what are the names of each pin?
eight!
1=Ground, 2=trigger, 3= output, 4=reset, 5=control Voltage, 6= Threshold, 7=discharge, 8= Vcc (+)
HOMEWORK QUESTION 3
What R1/R2/C1 values could be used for a 10 milliseconds On-Time pulse from an a-stable 555 timer configuration? (use Frequency = 5 Hz, 20 Hz and 50 Hz for 3 sets of R1/R2/C1 Vaues)


HOMEWORK QUESTION 4
If a 555 timer’s output signal has a period of 25 milliseconds, what is the frequency of this signal?
f=1/0,025=1600Hz

Hi Jonny,

Answers 1 and 2 are correct. #4 should be 25 mS = 0.025 = 1/0.025 = 40 Hz, it looks like you were on the right track but got mixed up at the end.

Is Question #3 too complicated? Let me know if you guys want, I can post a solution for it or make it a tad easier to solve.

HOMEWORK QUESTION 3
What R1/R2/C1 values could be used for a 10 milliseconds On-Time pulse from an a-stable 555 timer configuration? (use Frequency = 5 Hz, 20 Hz and 50 Hz for 3 sets of R1/R2/C1 Vaues)

this one has me at a stand still I've tried changing the final formula but all answers result to 100 so is R1/R2/C1 values all 100 ohm and farads?