Design Project

1 Circuit Design

The LEDs you're going to use are very bright, 1W models.
They'll work with a good-quality 9V battery, but because LEDs have very low internal resistance, if connected directly to the battery they'll draw too much current, quickly overheat and burn out.
To reduce the current flow and divide the voltage, we'll use a 56 Ohm, high power(2W) resistor connected in series with the LEDs, this will stop this from happening.
You're going to need to design a compact Stripboard circuit to take all the component parts. We use DIYlc for stripboard design in School.
Resource: You can load DIYlc from the open drive in School, in the G:\Design Engineering\Student Home software\DIYlc\ folder. Double-click the 'diylc.exe' file to start.
Resource: At home, DIYlc is available for download here.

Download this DIYlc file into your H: drive, and use File -> Open in DIYlc to open and view it. You can't just double-click on it.

This is an example of a stripboard circuit. A few important points have been picked out, which you might want to consider in your design.
- Strain relief holes only take a few seconds to drill, but will prevent your power wires from breaking off again and again.
- 3mm holes in the PCB will allow you to poke M3 machine screws through them to secure the lights at the bottom of your housing.
- The spot-face cut is to prevent the steel nuts we use from creating a short-circuit and burning out your LEDs.
You are seeing the finished circuit from the component side (the side with no copper tracks on it).
To make life a little easier, the tracks are also shown (as if you had X-ray vision).

Here you can see the path that electrons take through the circuit. Remember that the electrons are unable to jump over the thin gaps between the copper rows of stripboard.
Electrons travel in from the red wire, arriving at the middle row of the stripboard and attacted towards the negative end of the battery (black wire).
As the only route they are presented with is to travel through the + leg of the LED, they pass through here and emerge at the bottom.
From here, the only route the elctrons can take now is to travel through the 2W resistor, to the top row of the piece of stripboard.
Once at the top row, the electrons are able to travel up the black wire to the negative terminal of the battery, completing the circuit.

Using the example circuit provided to you above, use DIYLc to create the circuit shown above on a stripboard.
Tip: When inserted in stripboard, the LEDs occupy 3 columns and 3 rows.
Tip: You'll need to keep two 3mm holes to mount your PCB to the housing. Remember that creating a hole in a row of this size prevents current from travelling past that point in the row.
You will be awarded a badge for your work :
- Silver: All components added to stripboard design.
- Gold: Workable final design is 16x7 or under.
- Platinum: Design is 12x6 or under.