construction

lectronic Construction

Guy rope
warning
project

About the project
This years electronic construction project is a gadget, which will allow you to indicate where guy ropes are around the campsite. It will detect when it goes dark and automatically turn on and the LEDs will flash to warn people of the guy ropes so they don't trip over them.

There will be another mode where the gadget can be used in a search and find wide game. The gadget will be tied to a tree or similar. In this mode when a torch light is passed over the sensor the LEDs will flash quickly, thus indicating its location.

Electronic projects
In order to record the information about an electronic circuit, you need several different things:

Schematic diagram (a diagrammatic representation of the circuit)

PCB layout (A diagram showing where the warts should be placed)

Parts list (A list of all the parts that go into the circuit)

Schematic diagram

How it works
The decision of whether it is day or night is made based upon the resistance of a special resistor which changes its resistance as the amount of light which falls on the sensor changes. This part is called a Light Dependant Resistor or LDR for short. This information is fed into a microcontroller which is a mini computer designed to control electronics. The microcontroller runs some software, which by day does nothing and at night flashes the LEDs in sequence. A resistor is placed in series with the LED to control the amount of current which flows into it, thus controlling the brightness. In this design the microcontroller has a choice of resistors so that it can maintain the same brightness as the batteries become flat. The microcontroller also monitors the switch so that the device can be put into a near zero current drain sleep mode (turned off) and can enter the wide game mode.

PCB layout

Parts list

PCB Ref(s) Description Quantity
R1 1M resistor 1
R2 65R resistor 1
R3 91R resistor 1
R4 Light Dependant Res 1
R5 22K resistor 1
IC1 PIC 12F675 (microcontroller)
8 pin DIL socket 1
LED1, 2, 3 3 mm super bright LED 3
Conn1 PCB mount battery holder (2xAA) 1
SW1 PCB mount push to make switch 1

Operating instructions

To turn the device off, push and hold the switch for one second. The Outer two LEDs will flash and the device will be turned off.

To turn the device on, push and hold the switch for one second. The middle LED will flash and the device will be turned on.

To enter wide game mode press the switch three times in close succession. All of the LEDs will flash in quick succession.

To exit wide game mode turn the device off. When it is turned back on it will start in guy rope mode.

In guy rope mode, when dark, the LEDs will slowly flash in sequence.
In wide game mode, the LEDs will flash rapidly whenever the light level increases.

Back to electronic construction index

PCB Ref(s)	Description	Quantity
R1	1M resistor	1
R2	65R resistor	1
R3	91R resistor	1
R4	Light Dependant Res	1
R5	22K resistor	1
IC1	PIC 12F675 (microcontroller) 8 pin DIL socket	1
LED1, 2, 3	3 mm super bright LED	3
Conn1	PCB mount battery holder (2xAA)	1
SW1	PCB mount push to make switch	1