Make your favourite emergency vehicle with flashing lights, and learn about electronics at the same time!
BUILD TIME: 45 MINUTES
DIFFICULTY RATING: BEGINNER
So many kids get a thrill seeing an emergency vehicle driving up the road with lights and sirens sounding. Now they can build their favourite vehicle decoration with flashing LED lights to show off to friends and family.
At the same time, the kids will learn about electronics and be introduced to the versatile 555 Timer IC.
You can use the circuit on just about any cut-out design, but we’ve included a Police Car, Fire Truck and Ambulance for your kids to choose from.
We’re assuming very little (or zero) electronics knowledge, and so will try to walk through everything carefully, in order to ensure your success. There is no soldering or programming required - we’ve kept it as simple as possible.
If this is your first project, you may also like to read “Breadboard Basics” in Issue 15, to familiarise yourself with the breadboard before getting started.
COLOURING & PREPARATION
The printable parts can be printed on any home printer on an A4 sheet. While these are not critically essential, it helps make the builds more fun than simply LEDs lighting up without any context.
We have provided coloured and non-coloured illustrations for the projects. This is to allow you to either add-on the fun of colouring the interactive scenes, or simply get on with the interactive portion. The choice is yours.
For each design, you’ll need to bond the backing card to some cardboard. This will help provide structural integrity to the overall project. The paper itself is too flexible and will simply bend.
The cardboard should be thick enough to hold itself up, but not so thick you cannot easily cut it with scissors.
ELECTRONICS AND CONSTRUCTION
We will split the build into two parts. First, we will build the electronics that flashes the red and blue LEDs.
Then we will show you how to connect the LEDs to the Fire Truck, Police Car or Ambulance cut-outs.
The circuit is easily expanded and can drive up to 10 pairs of LEDs in parallel (that is, all positive leads to the same point, and all negative leads the same point).
|CRAFT MATERIALS & TOOLS REQUIRED:
|1 × Computer to Download the Illustrations
|1 × B&W or Colour A4 Printer to Print the Illustrations
|1 × Pointy Nose Pliers to Bend the Legs of the Electronic Components
|1 × Pair of Scissors / Artwork Knife
|1 × Glue Stick
|2 × A4 Sheets of Cardboard (Thick)
|1 × Pack Blu-Tack / Tape etc.
|Markers, Pencils or Crayons (if using outlined versions for colouring)
CRAFT MATERIALS & TOOLS REQUIRED:
|ELECTRONIC PARTS REQUIRED:
|1 × Small Prototyping Breadboard
|1 × Mixed Jumper Wires
|1 × Breadboard Wire Links
|1 × 555 Timer IC
|1 × 5mm Red LED
|1 × 5mm Blue LED
|1 × 10μF Electrolytic Capacitor
|2 × 470Ω Resistors*
|1 × 47kΩ Resistor*
|1 × 9V Battery Snap
|1 × 9V Battery
*Quantity shown, may only be available in packs
Let's build the electronics for our project. Over the next few pages we will guide you step-by-step on how to wire up the electronics. If you are unsure about any of the connections, you can refer back to the Fritzing diagram shown below. This diagram shows you the holes the components and wires need to be plugged in to. We should also point out that it doesn't matter what colour wires you use.
Before we get started though, arrange all of the parts, tools and materials required. Make sure you have a clean workspace with good lighting.
Put the breadboard on the table in front of you. The side with the blue (-) negative power rail should be closest to you.
Insert the two wire links on the left that join the positive and negative power rails on top to the power rails on the bottom.
Gently insert the 8-pin 555 Timer IC into the breadboard, making sure you put it in the right way. The notch or circle indent on the top of the IC should point to the left side of the breadboard.
Insert the wire link shown here that goes from pin 8 of the IC to the positive power rail on the breadboard.
Insert the wire link shown here that goes from pin 4 of the IC to the positive power rail on the breadboard.
Insert the wire link shown here that goes from pin 1 of the IC to the negative power rail on the breadboard.
Insert the three wire links shown here that join pin 2 to pin 6 on the IC.
Insert the two wires shown here.
Insert the 47k resistor as shown here. It can go in either direction. A 47k resistor will have yellow-violet-orange or yellow-violet-black-red coloured bands on it.
Note: We have trimmed the legs of our resistor with cutters and bent the legs so it goes flush to the board.
Next get your 10μF capacitor and work out the negative leg, which is identified by stripes on the casing.
Insert the capacitor so that the negative leg goes into the negative power rail on the breadboard. The other pin goes to 2nd leg of the IC.
Your capacitor should be in the breadboard like shown here.
Insert the wire link as shown here.
Insert the 470 Ohm resistor as shown here.
A 470 Ohm resistor will have yellow-violet-brown-gold (4-band) or yellow-violet-black-black-brown (5-band).
Insert the other 470 Ohm resistor as shown here.
Using some pliers, make a very small bend in each LED leg. This small bend will help them stay in the connector, which we will detail in the next step.
Push the legs of the LED into 10-15cm long jumper wires as shown here.
LEDs only work in one direction. Use a black or dark coloured wire to connect to the negative leg, which is the short leg. The flat edge in the round plastic top is another way to work out what is the negative side. The longer leg is the positive leg. Use a red or similar coloured wire on this one.
If the LED falls out from the connector you will need to bend the leg of the LED a little more.
Connect the LEDs as shown here remembering that one leg is positive and the other is negative.
Here’s a close-up view of the wires in the breadboard.
Plug the 9V battery snap into the breadboard. The red wire goes into the positive (+) rail on the breadboard, and the black wire into the negative (-) rail on the breadboard.
The LEDs should start flashing alternatively when you connect a battery.
If your circuit is not working, here are some tips that may help:
- Make sure the battery you are using isn’t flat
- Make sure all the wires and components are pressed firmly into the breadboard
- Compare your wiring to the Fritzing diagram to make sure all the wires and components go into the same holes
- Check that the capacitor is in the correct way with the stripes pointing to the negative rail on the breadboard
- If both LEDs flash at the same time instead of alternating you may have put one of the LEDs in the wrong way
These steps work for any of the design.
Prepare the tools and materials to make the backing support piece.
Apply glue to the thick backing card and stick on the backing support template. Leave to dry.
Carefully cut out the two support pieces
Fold the first support piece indicated by the three black lines.
Glue the first piece together to form a triangle, then repeat Step 4 to fold the second support piece.
Glue the second piece together. You should now have two triangular support pieces. Set aside to dry.
Prepare the tools and materials to make your chosen printed design. We’ll use the Fire Truck in our example, but the same process applies to the Police Car and Ambulance.
Apply glue to the back of the printed design.
Glue the printed design to the thick backing card. Leave to dry.
Very carefully cut out the two 5mm holes for the LEDs.
Glue the two backing support pieces to the back of the printed design. The pieces should be positioned at the bottom so the design will be able to stand like this. Leave to dry.
Next, insert the LEDs. If the LEDs are loose you could use some Blu-tack or tape on the back to stop them falling out.
Connect your 9V battery and you should see the LEDs flash.
Congratulations, you have just made is a simple timer circuit using the versatile 555 Timer IC.
The 47k resistor and the 10μF capacitor set the timing at which the 555 timer turns pin 3 "on" and "off", better described as High or Low. The ratio of the High time and Low time is referred to as the 'Duty Cycle'.
If you change the value of the 47k resistor, or the 10μF capacitor, you effectively change the duty cycle, which results in the LEDs flashing at a different speed.
We have used a common 9V battery to power our circuit, but the 555 Timer IC is designed to work from any voltage between 4.5V to 15VDC. If you didn't have a 9V battery you could use, say a 4 way battery compartment with 4 x 1.5V batteries, which would be 6V.
Our LEDs only need 2V to 3V to light up. The LEDs may get damaged if we connect them straight to the 9V battery, which is why we have 470 Ohm resistors in series with each resistor.
You can learn a lot more about the 555 timer in our first DIYODE issue #001.
WHERE TO FROM HERE?
Make your own designs. You could use two red LEDs and make lights for a train level crossing, for example. Swap for two orange LEDs and make a construction scene with flashing warning lights.
You can add more LEDs too if you want. The 555 timer will handle up to 200mA of current, which is about 10 standard LEDs. You can put these LEDs in parallel with the current LEDs.
As mentioned in the summary, you could change the speed that the LEDs blink by changing the 47k resistor or the 10μF capacitor. Experiment with different values or go to this website to see how different values affect the timing: http://www.ohmslawcalculator.com/555-astable-calculator
Other coloured LEDs, and 3mm and 10mm diameter LEDs are also commonly available. High-brightness LEDs will provide spectacular results too. The best resistor for each LED type depends on the battery voltage and the LED current. To prevent the LED burning out, the best resistance should be calculated for each, but you can start with a 1000 Ohm resistor, and if it's not bright enough try the next smaller resistor, 820 Ohms, 680 Ohms etc down to 100 Ohms.
If you get creative you could add the LEDs to a plastic model car or a Lego set. The circuit is quite versatile.