# Design Project

## 1 Circuit Design

### Learn It

• 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.

### Try It

• 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.