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What can a 555 Timer do?

Our maker space, The Rabbit Hole recently had a Jameco build night where we (this project was worked on by group members Mazzmn, Hydrotron and theZuke)  experimented with 555 timers and other cool stuff. This Instructable demonstrates using a 555 timer to create a "Basic Astable Circuit" that blinks an LED. It's based on a circuit by Forrest Mims III but we've added an extra capacitor and a switch to allow for "Turbo Mode" where the blinking LED blinks extra fast! 

Parts needed for the Turbo Time 555 Timer Demonstration Circuit
  • 1 - LM555 IC
  • 1 - 100uF Capacitor
  • 1 - 12uF Capacitor
  • 1 - 1K Ohm Resistor
  • 1 - 10K Ohm Resistor
  • 1 - 15K Ohm Resistor
  • 1 - 4.7K Ohm Resistor
  • 2 - Pots 
  • 1- Solderless Breadboard
  • Misc jumpers and wires 
  • 1 - 9V battery
  • 1 - 9V battery adapter

Gather materials and let's build!

(This Instructable submitted by the Rabbit-Hole Maker Space as part of the Instructables Sponsorship Program.)

Step 1: Let's Build the Circuit

Let's Build the Circuit

The schematic shown in this Instructable was created with Fritzing 0.8.3 and should look very similar to a real circuit you can build. The colors of the resistors are even accurate for the recommended resistance level.

It's a good idea to start by gathering the components you need.
Another tip is to print the schematic and lay each component on it's proper location on the diagram.

The Breadboard:
The solderless breadboard (sometimes refered to as a protoboard) allows you to protoytype a circuit and reuse components.
The long lines of holes where attach the battery are called rails. All the holes on the red rail are connected and the same is true for all the holes on the blue rail. Although the top rail and the bottom rail are not connected. T
The short 5 long groups of holes (running vertically in the image included here) are called rows.
All 5 holes of a row are connected, but are not connected to any adjacent rows or the rails.

Circuit Assembly:
  1. Start with the Battery connector (but don't plug in a battery, it's a bad idea to wire a live circuit) and connect the + wire to the red rail and - wire to the blue rail.
  2. Next place our Integrated Circuit (IC) the 555 timer chip (note the orientation, the notch goes on the left hand side in our diagram and the lower left hand pin is pin 1
  3. Next work your way around the circuit, clockwise or counterclockwise whichever you prefer. 
  4. Note how the red wire brings power to pin 4
  5. Note the orientation of the Capacitors
  6. In the diagram the black wire connects to the common pin of the switch.
  7. Note the orientation of the LED, the longer pin is Positive and the shorter pin plugs in to the blue rail. 

  

Step 2: How Does the "Turbo Time" 555 Timer Work?

How Does the "Turbo Time" 555 Timer Work?
The original circuit is published in Engineer's Mini-Notebook - 555 Timer IC Circuits by Forrest M. Mims III on page 7.
We started out by simply building the basic circuit...but for a demonstration, let's say there was a lack of pizzazz  as it didn't make noise or even have a single blinking LED!!

So ....we added a current limiting resistor and LED to pin 3 ..that gave us the blinking LED
But then we also added a "Turbo" in the form of a smaller capacitor (~ 1/10 the original capacitor). Since the new capacitor is smaller it charges and discharges faster....thus the LED blinks faster.

Terms:
Period : 1/Frequency (.1 sec period = 10 Hz)
Duty Cycle : Percentage of the time the signal is high.
(25% duty cycle = 1 second high 3 seconds low)

Description:
Technically: In the Engineer's Notebook, you'll notice that the output signal of the circuit is characterized by the 2 resistors and the capacitor.  The overall frequency is the inverse of the period, the period is the sum of time high and the time low.

1/FREQ = T = TH + TL
where:
tH = .693 * (r1+r2) * c1
tL = .693 * (r2 ) * c1

TH = time High
TL = time Low
T = Period
R1 & R2 values of resistors
C1 Value of capacitor

Looking at the math the simplest way change the frequency is to change the size of the capacitor. So to get a higher frequency  ( shorter period ) lower the capacitance.  So to demonstrate this we decided to switch between 2 capacitors, with a micro switch. That way we'll connect to one when the button is not pressed and to the other when it is.  If you think about it, this might cause switching discontinuities.  It is left to the reader to consider layouts that might prevent these from occurring. (Hint:both caps are temporarily disconnected during switching.)

Check out the video included here to see the circuit in action

Thanks for checking out our Instructable and good luck with all your projects!
<p>Grate ible </p><p>thanx</p>
<p>thanks!</p>

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