Flashing Eye Robot / Teaching Electronic Circuits

Flashing Eye Robot
Multivibrator circuit
Clubjesmiddag 18 Mar 2014
Adam Dorrell

Adam Dorrell / Clubjesdag 18 Mar 2014
What this is
• Produce a “Flashing Eye Robot”
• Learning basic electronic circuit
• Agenda
– Build and understand basic LED circuit
with switch
– Make a flashing light circuit with 2
LEDs and 2 transistors
• Technical name: “astable multivibrator”
– Understand how it works
• Advanced
– Change some components to change
flashing rate
– Two LEDs 1:1 duty cycle also 1 LED
like lighthouse 1:10 duty cycle
– Make a lighthouse

Our first circuit
Electricity
BatteryResistor
Push button switch

Battery
• A source of electricity
• We will use a 9v (9 volt) battery
• Electricity flows from + to -
• DO NOT LET THE WIRES TOUCH!
– This will cause a short circuit.
– May cause a fire, will certainly flatten
battery!

LED
• LED is a “Light Emitting Diode”
• Invented in 1962
• Light is produced directly from electricity
• Can only work one way round
– Long lead goes to +
• Needs a resistor (or it burns out)

Resistor
• Resistor reduces voltage level
• It “squeezes” the electricity,
letting only some of it through
• They are measured in “Ohms”
• Symbol: Ω or R
• Today we will use 2 types:
– Orange-Orange-Brown-Silver
= 330R = 330Ω
– Brown-Blk-Yellow-Silver =
100K = 100,000Ω

Push button
• Makes a contact when pushed
• Completes our circuit and allows electricity
to flow through it

Learning about the breadboard
Row 1
All holes in the selected column are internally connected.
Row 10 etc

Circuit Layout – Simple LED
330Ω
Breadboard
LED D1
R1 – 330R
Button
+9v -9v
Battery

Our first circuit – on the breadboard
What happens when you push button?
What happens if you have the LED in the wrong way?

LED Circuit

Press the button

2. Flashing Light Circuit
• We can make a simple circuit to
flash LEDs
• It uses 2 transistors as switches
• Also capacitors to store the
electrical charge, for the length of
flash
• This is the basic part of any
computer

Circuit Diagram - Flashing LEDs
Battery
Transistor
Capacitor
Correct name: Astable Multivibrator

Transistor
• Invented in 1947
• A transistor is a “Switch”
• It is in every item of electronics
• In an iphone or computer, there are
1,000,000s in a tiny “chip”
• Today we will use a BC547
– It costs EUR 0.10
B = Base
C = Collector
E = Emitter
BC547 NPN bipolar transistor

Capacitor
• A capacitor stores electricity
– It holds an electrical “charge”
for some time
– We use it to make the switch
stay on for about 1 second

Building it 1
Put in the 1st transistor Make sure it is in the right way!
C – B - E

2
Put in the 1st LED.
Make sure it is in the right way
Long lead goes in row 1
Row 1

3
Add the power leads
Red goes in Row 1
Black connects to the transistor (E – Emitter)
DO NOT CONNECT THE BATTERY YET!
Row 1 (+)
Emitter of transistor (-)

4
Put in the 1st resistor
This is the 330R resistor (orange, orange, brown)
Row 2 to the transistor (Collector C)
You can bend it into shape

5
Add the small yellow wire to Row 1
This connects the (+) up the two halves of the circuit

6
Now add the 2nd resistor.
This is the 100K resistor
Brown-Blk-Yellow-Silver = 100K = 100,000Ω
It connects from row 1 to the centre of the transistor (Base = B)

7
Add the black wire to the transistor E connection (-)
This will supply the (-) power to the other half of the circuit

8
Add the 1st capacitor.
This connects to the C Collector of transistor
1 and the B Base of
transistor 2
Add the 2nd capacitor.
This connects to the B base (centre) of
transistor 1 and the C Collector of
transistor 2
BE CAREFUL NOT TO LET THE WIRES
TOUCH!
Don’t let the wires cross
⊖
⊖

9
Connect the yellow wire
Add resistor 4
This is the 330R This is the 330R
resistor (orange, orange, brown)
Row 2 to the transistor 2 (Collector C)
Now add the 3nd resistor.
This is the 100K resistor
Brown-Blk-Yellow-Silver = 100K = 100,000Ω
It connects from row 1 to the centre of the
transistor 2 (Base = B)

10
Bend the resistor
into shape
Don’t let the wires
touch

11
Connect the black wire
Add transistor 2
Take care to put in the right way!
⊖
⊖

12
Add LED 2
Careful to put in the right way!
The long lead goes into row 1

13
Now you can connect to the battery!
Let’s check it works!

Circuit Layout – Flashing Lights
+9v -9v
LED D1
LED D2
Q1 BC547
R1 – 330R
Q2 BC547
R2 – 330R
R4 – 100K
C2 10u⊖
R4 – 100K
C1 10u
⊖
Battery

Making the Robot

How it works
Battery
Transistor
Capacitor

How it works 2
Battery
Transistor
Capacitor

Advanced (if time)
• Change colour of LEDs
• Add more LEDs
• Change the values of the resistor and capacitor
• Make the flash 1:10 instead of 1:1

Parts list
• PARTS LIST
– 2 x BC548 NPN transistor
– 2 x LED 10mm mix colour
– 2 x 330R resistor (0.5w)
– 2 x 10u Capacitor
– 2 x 100K Resistor
– 1 x 9v battery
– 1 x 9v holder
– 1 x button 6mm sq
– Small breadboard
• PARTS LIST (NL)
– 2 x BC548 Bipolaire NPN transistor
– 2 x LED 10mm mix kleur
– 2 x 330R weerstand (0.5w)
– 2 x 10u Elektrolyt condensator
– 2 x 100K weerstand
– 1 x 9v 9V batterij (blok)
– 1 x 9v Batterijclip
– 1 x Druktoets 6mm sq
– Insteekprintplaat

Flashing Eye Robot / Teaching Electronic Circuits

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