555 circuits
The basic electronics that underpins boards like the Arduino can be unpacked by examining how some basic integrated circuits operate. One of the most versatile integrated circuits to experiment with is the 555. It is a small electronic package, but has a great deal of potential. To start, use a fresh breadboard and assemble the parts as shown in the diagram:
Review the connections by making sure each pin is connected as follows:
Pin 1 (by white dot on chip): blue wire to negative strip
Pin 2: Connect with orange wire to pin 6 and connect it to the 22 mfd electrolytic capacitor + side
The negative side of that capacitor goes to the blue ground strip (negative of battery)
Pine 3: Connect a yellow wire to the long side of an led
The short side of the led goes to the blue ground strip (negative of battery)
Pin 4: Connect with red wire to red positive strip
Pin 5: No connection
Pin 6: (Orange wire to pin 6) Connect 10 k resistor from pin 6 to pin 7
10K resistor is painted Brown-Black-Orange
Pin 7: (10k resistor to pin 6) . Connect another 10K resistor to pin 8.
Pin 8: Connect to positive red strip
You can also build the circuit directly from the schematic below. For our purposes, the following changes must be made from the schematic: we would use a 10K resistor instead of a lK; a 6 volt supply instead of 3 V and a 22mfd capacitor instead of a 100 mfd. Notice that this is just another way to follow instructions to build a circuit.
Test your circuit by connecting your battery supply: positive, or red, from the battery supply to positive, or red, strip and negative to blue on your breadboard. If all is working properly, you should have the LED blinking! This is a timer circuit that blinks with regularity depending on the values of the resistors and the one capacitor.
Variable Flasher
Let's change one of the variables in the system. The resistor that is placed between pin 6 and 7--let's replace it with a variable resistor called a potentiometer. Note the picture below.
In a schematic the variable resistor look like this:
Try adjusting the variable resistor to see the effect.
Audible System
Next, replace the LED with a diode and speaker as shown below. Remember to connect the battery as always--positive to red, negative to blue.
Instead of an LED flashing, you should hear a click. Rotate your variable resistor (potentiometer). What is the effect?
Counters
Let's go one more step and use the pulses of the 555 to drive a counter. Let's add a new integrated circuit, the 4017 counter. Here is the schematic for adding the 4017. It is getting a little complicated!
To make this easier, let's do this in two steps:
Step 1:
Connect wires as shown:
4017 Chip
Pin 8: Connect with blue wire to blue strip, negative
Pin 13: Connect to blue negative strip
Pin 14: Connect to pin 3 of 555
Pin 15: Connect to blue negative strip
Pin 16: Connect to red positive strip
STEP 2
The rest of the connections are LEDs.
Connect pin 1, 2, 3, 4, 5, 6, 7, 9, 10, 11 each to the long side of an LED. (see example for pin 1 below). The short side of each LED will be connected to the blue negative rail.
The diagram above just shows 1 LED. You will need to add 9 more!
Power up the board. What have you created?
Engineering Challenge
The 555 circuit creates a pulse. If the pulse has a long interval, the counter will count slowly. LEDs on the counter can drive the motor controller for the 2D plotter. How can you replace the Arduino with the 555 and 4017 electronics to draw a diagram?