D&T: Electronics and Control Systems

Name: David Potter

Candidate Number:

Centre Number: 16527

Unit A511: Introduction to Designing

SecurityBy David Potter

CreativityThe theme for my project is security. I have chosen this theme because millions of pounds are spent each year on replacing items stolen from their house and replacing damages after things that may have happened to them, so I think that a security device will make people feel safer as well as be safer. You can use a security device to protect anything and they can range in prices dramatically, so many people get burgled every year and that could all be stopped by one device per household. I think this makes security a perfect theme for my product.

Here I have highlighted my chosen product that I am going to produce. I have chosen this because there is a need for it in the market.

Creativity

User Needs

Who

When

Where

Why

What

People with Dementia.

People worried about their bath overflowing

Universities

Homes Hostels and Hotels

Mornings and evenings when bath is being used most

Anytime that the bath is used.

Because they have expensive items to protect.

Scared of bath overflowing

Previous experience

Bath overflowing

CreativityIf people buy this product then they can feel safer when leaving the bath running while they do something else. People with Dementia might want this product because they may forget that they left the bath on.

Here is a newspaper article showing a bath that overflowed in a university. My device could have been used here and could have stopped much disruption.

Here are some pictures of a bath overflowing. My device would stop this in both cases. This shows that there is a need for my product in the market.

Here is a quote from a student from a university where a bath overflowed and caused great disruption "If we're having our lecture time cut down by 20% is there any way we can reclaim 20% of our tuition fees? It seems only fair."

Here is another example of a bath overflow causing serious trouble. This shop was flooded after a neighbours bath overflowed.

None of these problems would have occurred if they had had my product. This also shows that there is a definite need for my product.

Survey Reasons For Questions1. No point in product without bath

2. Wouldn’t be useful for someone who didn’t bath a lot.

3. Main point behind product, if they don’t leave it running they don’t need the product.

4. Would the product need to be adjustable.

5. The leading cause of bath overflows is people with dementia forgetting they left the bath running.

6. To see if they already understand the risks of not having the product.

7. Again to see if they understand the risks of not having it.

8. To see how popular other devices are.

9. To see what would be a reasonable price to sell it at would be.

10. What would make it most appealing to the customers.

From the survey I have done I have found out that most people leave the bath on while they do something else, are frightened of their bath overflowing, would be willing to pay £10 and would want both sound and light as an output. I have also learnt that the majority of people have a bath once a week which means that there is a definite need for my product because people have baths quite often. I have also learnt that it will need to be adjustable in a bath because different people have baths at different heights.

Other Security DevicesProduct Price

Typical userWhen / Where used?

Function

Technology used(Input / Output)

Manufacturing process used

Surface Magnetic Contact 1 Pack HWSMC1

£1.45

Magnetic contact which detects when the door is opened. Can be used by anyone on a window or door.

To detect when a door or window is opened and set off an alarm when it does.

Magnetic contact to detect when the door opens and then alarm goes off when it happens.

Injection moulding, for casing, vacuum forming for packaging and PCB manufacturing for circuit.

Home Security Motion Sensor Alarm with 2 Remote Control

£4.85

Simple motion sensor to scare away burglars and protect a house or door. Could be used by anyone who wants to protect their house.

To detect movement and set off alarm if it does. Sound can only be turned off if a button is pressed on it.

Infrared sensor to sense movement, alarm to go off if it does and an LED to show it is turned on and working.

Injection moulding for casing, vacuum forming for packaging and PCB manufacturing for the circuit and assembly.

Yale wire free Premium Alarm Kit HSA6400

£179.99

Hi tech infrared sensor to detect movement outside a house. Can be used by anyone who can afford it and wants to protect their home.

To detect movement and set off an alarm and call three numbers that you put in if it does. Can only be turned on and off by a keypad lock.

Infrared sensor to sense movement, alarm goes off if it does and phones number you put in when it does.

Injection moulding for case, vacuum forming for packaging and PCB manufacturing for circuit.

From this I have learnt that generally the more expensive the item, the more sophisticated it is. This makes sense because the complicated something is, the higher level of technology is required which is generally more expensive.

Design Brief

So far I have discovered that there is a definite need for my product and peoples baths flooding is a reasonably big problem. I have discovered that a lot of people are scared of their bath overflowing from my questionnaire and that people with dementia would like the product a lot because people with dementia forgetting that they have left the bath on is the leading cause for bath overflows.

I am going to design and make a bath water height alarm. It will detect when the water level gets to a good height, a too high level and when it is about to overflow using three moisture sensors. At each level there will be a light green at a good level, orange for warning and a red light and an alarm when it is way too high. It will have a sucker on the back so that you can adjust it according to the size of your bath and how high you like your bath. I will use circuit wizard to design the circuit and PCB and will then solder on the components.

SpecificationFeature Described Reason For Feature

The purpose of my product is to alert someone that the bath water is too high.

This is because I have researched that there is a real need for my product as overflowing baths can be devastating.

My product needs to detect moisture levels in a bath and display that information.

This is because it needs to fulfil its purpose and also because I have researched that popular products show three or more moisture sensors.

My product will need to detect 3 water levels in a bath. This is because it needs to fulfil its purpose.

The power source of my product will be a battery. This is because it is a good, portable source of power and my product cannot run on mains.

The circuit will run on 9V. This is because the battery I will be using is 9V and it is a good voltage for the circuit.

My product will have an on/off switch. This is because you can then turn the circuit off when it is not in use to save battery power.

My product will also have a power indicator. This is because my device is battery powered so it is a good way of testing whether the batteries are good.

The outputs of the product will be 3 LED’s and a Buzzer/Siren. This is because I discovered in my questionnaire that people want both an LED and buzzer.

The circuit will be designed using circuit wizard. This is because it is a simple and easy way to create quite complex circuits.

The circuit will be manufactured using the denford to create the PCB and then I will solder the components on.

This is because it is the best way to do it using the schools equipment.

I will insure that the circuit will be well made and will work by testing the circuits at several stages and by making sure all soldered connections are well done.

This is so that the user can use it without fear of the product breaking.

Product Analysis

Water Leak Alarm - Water

/ moisture / flood detector sensor

Rialco Water Flood Alarm

Function To detect water leakage and moisture and to set off an alarm when it does.

To detect when water reaches a certain level in a bath and to ring an alarm when it does.

User need fulfilled

Yes because it is multipurpose and performs everything written in its description and does everything that it should.

Yes because it detects water when it gets to a certain height and does have an alarm which goes off when moisture reaches that level.

Materials used in construction

Plastic, PCB, Components PCB, Components, Plastic

Durability of product

Reasonable, made of medium quality plastics, would probably break however if dropped.

Reasonable, not as durable as the other, more fragile, would break if dropped

Sustainability (6Rs)

Is not reusable really, plastics could be recycled. Internal parts may not be recycled.

Not reusable, plastics could be recycled, internal parts may not be.

Life cycle Could be mostly recycled, pretty cheap to make, pretty poor durability. Life length:2 yrs

Cheap to make, poor build quality, could be recycled. Life length:3 yrs.

Energy use Batteries, does not use mains power. Batteries, does not use mains power.

System Diagram

Delay before INPUT INPUT

Delay after INPUT PROCESS

Delay before

OUTPUT

OUTPUT

Time it takes for bath to fill up.

Float Switch / Transistor / LED’s

Time it takes for bath to fill up.

Probes / Darlington Pair / Siren

Time it takes for bath to fill up.

/ / MOSFET / Buzzer

Time it takes for bath to fill up.

/ / Comparator / Motor

Time it takes for bath to fill up.

/ / Astable / /

Time it takes for bath to fill up.

/ / Thyristor / /

Circuit Research

This circuit would be quite good for me but it is too simple and not tailored to my needs as I would need three moisture sensors and 3 LED’s as well as a buzzer

This circuit would be reasonably good but for the same reason as before it is not suited to my needs and is too simple. It also only has one output when I learnt from my questionnaire that I would need more than that.

This circuit is very good but is way too complicated, it covers all of my needs and more but it is way to complicated to reproduce and would be too difficult to do.

Circuit Research (continued)

This is quite a good circuit but it lacks numerous inputs and outputs that I found was wanted by people in the questionnaire

This circuit is perfect for mine and the users needs because it contains the necessary number of inputs and outputs, and it works in the way required. As found out in the questionnaire the users want more than one output and this is put in perfectly in the circuit.

Circuit Development

The first development I felt it necessary to make is to change the colours of the LEDs from three reds to green, red and yellow LEDs to make it more understandable.

The second development I felt it necessary to make was to add a power indicator onto it because I said I would in my specification because the circuit runs on battery power.

Circuit ProofHere are some images to show that my circuit works as it should.

This first image shows that when the power is on the power indicator is on and first button is pressed (the first water level reached) the first light turns on.

This second image shows that when the second button is pressed the second light comes on.

Circuit Proof

This final image shows that when the 3rd and final button is pressed, the final LED and a buzzer comes on.

PCB Testing

Here we can see that when there is power, the power indicator light is on. When the bath water reaches the first water level (switch 1) the first LED comes on. When the water reaches the second water level (switch 2) the second LED also comes on. And finally when the water reaches water level 3 (switch 3) the final LED and a buzzer come on. As the water level goes back down, the LEDs turn off.

Testing table

Stage Circuit PCB Finished Circuit

When power is on power indicator LED is on. YES YES ?

When water reaches first water level, green LED turns on.

YES YES ?

When water reaches second water level, orange LED turns on.

YES YES ?

When water reaches third water level, red LED and buzzer come on.

YES YES ?

When water level goes back down, each LED and the buzzer will turn off.

YES YES ?

PCB Development

Here is the first stage of PCB development, this is it when it has first been converted to a PCB.

Here I have moved all of the components around several times to allow 100% complete connections. An

Here I am testing the version of the circuit to make sure it works before developing it further. It does so I can move on further.

PCB Development (continued)

Here I have moved the components around again in order to put them into a smaller space, and therefore create a smaller PCB and saved money. Testing it shows that it works perfectly so I am ok to move on.

Here I have changed the pad sizes and hole sizes of all the circular pads in order to make soldering easier and save money.(It is in artwork view to make this easier).

Plan of ManufactureProcess Description Equipment Required Safety Issues Tips For Success

Design PCB and mask Circuit Wizard None None

Cut board to size Band Saw Saw is very sharp, do not put fingers anywhere near it.

None

Expose mask and PhotoPCB to UV light

UV light, PhotoPCB, Mask of circuit

UV light is harmful and can damage your eyes.

Expose for 10 mins.

Develop exposed PCB Development Fluid Development fluid is corrosive.

Wear gloves + goggles

Etch PCB Etchant, Bubble etch tank Etchant is corrosive Wear gloves + goggles

Drill Holes Drill, Drill clamp None Make Sure drill is centred over hole.

Solder resistors Soldering iron, PCB Soldering iron is incredibly hot.

Check value of resistors before soldering

Solder MOSFETS Soldering iron, PCB Soldering iron is incredibly hot.

Solder on right way round

Solder LEDs Soldering iron, PCB Soldering iron is incredibly hot.

Longer leg is positive one

Solder Off-Board components

Soldering iron, PCB Soldering iron is incredibly hot.

Feed wires through board before soldering.

Shrink wrap connections between off board components and wires

? ? ?

Equipment Used

Bill Of Materials

Circuit Making

First the LED wires must be tinned and soldered to the wires, here is me soldering the negative leg of the yellow LED to a black wire .

PIC I NEED TO GET FROM ED

Next I heat shrunk all, the wires to add strength.

This is what the heat shrunk LED looks like.

Then I had to repeat the past two steps for all the other off board components.

Circuit Making

Circuit Making

Photo I need to get from ed

Then I had to solder in all of the on board components on to the PCB

Here is all of the onboard components soldered on.

Description of ProcessU What went well (what did you do to avoid errors)

Problems Encountered Action taken to deal with problem

Design PCB and create mask

When designing the PCB we did several developments from the original and saved and tested it at each stage.

/ /

Expose mask and photoPCB to UV / / /Develop exposed PCB / / /Etch PCB / / /Cut board to size / / /Drill holes in solder board / / /Add Resistors Made sure I checked the colours

on the resistors before soldering them in.

Accidentally soldered a resistor into the wrong hole.

Desoldered it using soldering iron and resoldered into right hole.

Add MOSFETS When putting them in I made sure to not press them too hard and therefore damage them.

/ /

Add off board components I used red and black wires to show positive and negative legs .

Just used half the holesCircuit was designed using push button switches instead of probes so there were too many holes.

Manufacturing improvements that could be made:

Functional improvements that could be made:

I used a wrong sized heat shrink tube on one of the probes so it does not fit very well and the probe was difficult to fit into the plastic holder.

Power indicator LED could be a different colour that isn't red like green because red has the connotations of being bad.

The length of the wires attaching the probes to the PCB is too long so they get tangled easily.

The circuit could have a power switch so that the user would not have to unplug the battery every time they wanted to turn it off.

/The probes could be adjustable so that people could adjust them according to the size of their bath.