D&T: Electronics and Control Systems Unit A511: Introduction to designing and making

D&T: Electronics and Control Systems

Unit A511: Introduction to designing and making

Name: Jamie Hilton

Candidate number:

Centre Number: 16527

The theme for my project isSECURITY

“the state of being free from danger, damage, or worry.”Definition from Collins English dictionary

Why I chose securityWith more and more household technologies being available to the market there has been a sharp increase in what the value of goods being contained in households are and this creates an ever increasing danger of those goods being stolen and many burglars know how to get past a simple mechanical lock whereas if the lock was electronical and hooked up to an alarm it would still do the job of the lock and more. But security isn't just about keeping goods safe its also about keeping people free from worry and electronics can easily do that whether its alerting someone that their bath is about to overflow or if their child's food is too hot. Electronics can enhance security massively because in some aspects its smarter than the human mind. So I have chosen electronics because I feel it has a wide range of electronic products I can make.

What Could I Make?To begin to create a reliable security circuit I must first address a security problem to help me in deciding this I have created a mind map listing different problems and listing possible circuits to address the problem

The problem I have decided to solve the problem of household safety, specifically child safety around the bath by creating a bath temperature alarm.

USERS NEEDS

Users needsWhat is the problem?My user will want my device to alert them when their child’s bath water has become dangerously hot.

When will my user need it to work?My user will need it to work when the bath water for their child has become too hot.

Who is my products intended user? My products intended user is a parent that has a child who is old enough to use a regular bath but still need supervision when around a bath

Why does my user need this product?My user needs this product to ensure their child's safety while in the bath

Where will my user use this product?My user will use my product in their bath.

Evidence An 8-month-old baby has been taken to Children’s Mercy Hospital in Kansas City for treatment of burns received while receiving a bath.According to the Lyon County Sheriff’s log, the baby’s 11-year-old sister was preparing to bathe the boy and forgot to add cold water to the bath.He was taken to Newman Regional Health and transferred to Children’s Mercy with second-degree burns. He was in fair condition this morning.

Newspaper article taken from the “empire gazette”.

If this household did own a bath temperature alarm then the 11-year old sister would have known the water was too hot and it would have stopped this child from receiving burns.

This evidence leads me to believe that my intended user would be the person in charge of supervising a young child around the bath.

this cartoon illustrates that my temperature alarm would be used in the bath.

This is a picture of my intended user. a parent that has a child who is old enough to use a regular bath but still needs supervision when around a bath

Every day 10 children receive serious burns from hot bath water, a total of 3,500 each year. Two children die each year as a result of injuries caused by very hot bath-water. Many children under three suffer 20 to 50% body burns. Extensive plastic surgery is common.

Taken from the BBC news website

This evidence proves that babies and young children are all at risk around a hot bath.

This also proves that my product should be intended to keep children under three safe from harm

Questions Yes no1. Has your child ever been in any kind of danger around the bath?

2 8

2.Do you currently have any way of measuring the temperature of your child's bath?

2 8

3.Would you consider buying a device that could tell/alert you of the temperature of your child’s bath

9 1

4. Would you use such a device every time your child is in the bath?

9 1

5. Would you feel confident using such a product? 7 36. Do you ever worry about your child's water being too hot? 8 27. Do you think a system with an indication method (possibly LED’s) is a good idea?

7 3

8. Are you aware of any other temperature measuring devices?

8 2

9. Would you recommend such a device to other parents? 7 310. Do you think the bath can be a dangerous place for a child?

8 2

This is the questioner I got people from my local area to fill out. Before I got them to fill it out I explained what my intended product was. Each question helps me to understand who, what, when and where. Before asking them these questions I made sure they had a child between the age of 8-22 months.

Questions 1,5,6 and 9 help me to understand what problem my device should address and what specifications it must have.

Questions 3,4,5,7 and 8 help me to understand who my intended users are and whether they would use it.

Question 1 and10 help me to understand where my product will be used.

Question 4 helps me to understand when my product will be used.

Questionnaire resultsThe results from my questionnaire have told me that:• There is a need for my product because there are a number of parents are aware of the dangers of the

bath and are worried about it. • Most parents don’t currently have a way of judging the temperature of the bath water other than their

own judgement.• Those parents that are worried about their child's bath would be willing to buy my supposed product and

use it every time their child is in the bath and that most parents would feel confident using it. • The parents would want an alarm feature to alert them when it is too dangerous for the baby to enter the

bath. • My product would have to stand out as it would be competing with other devices that parents are familiar

with on the market.• It would be bought by many parents as it would have been mentioned to them by other parents proving

there could be a market with such a product.

Comparison of products related to my theme

Product CostTypical user

When / Where used?

FunctionTechnology

used(Input / Output)

Manufacturing process used

£17.99

Can be placed on windows, wall and

ceilings, typical user would be someone

afraid of breaking an entering through the

window

A small alarm the detects the

sound of breaking glass

Input is a microphone that can detect the

breaking of glass over a surface connected to a

90db alarm

Cheap plastic, probably ABS moulded to house a PCB circuit bored

£18.20

Good for using outside a door. User would be someone

who is worried about their security

Wireless alarm with motion

detection and remote alarm.

Input is a infrared motion detector with

10 meter range to detect movement in a dark environment

connected to a 90db alarm

Still using a cheap plastic, probably ABS also, injection moulded to house a PCB

board.

£99.95Used out side house. Works whenever the user arms it till when they disarm it. Ideal for homes with the elderly or children.

An alarm system that has the

ability to connect multiple

inputs for adaptability.

Included in the default house hold package is a

microphone based window and door contact

sensor to detect the sound of some smashing the window or breaking

the lock on a door connected to a 95db

alarm

A more expensive plastic

is used, as indicated by the price, to house a

more complex series of circuits

König Wireless Alarm with Motion Detector

Friedland Response SL1 Home and Away Wirefree Burglar Alarm System

Texecom AEC-0001 Impaq Glass Break Detector

Comparison reviewThe trend identified by the table on the previous slide shows that the higher the price the more

complicated the system, for example, the “Texecom AEC-0001 Impaq Glass Break Detector” is the cheapest and is a simple device which only requires the user to install and turn it on, and is made from cheap materials. Whereas the “Friedland Response SL1 Home and Away Wirefree Burglar Alarm System” is the most expensive and complex and not only requires the user to install and turn it on but also to arm it and set preset codes to reset the alarm, it is also more versatile as it can adapt to use more inputs, it is also made to last by using more expensive materials ensuring the customers gets their monies worth.

More detailed comparison

The Texecom Impaq Glass Break provides protection from an intruder coming through the window. The Impaq Glass Break is an acoustic glass break detector designed to provide warning of a potential intruder by detecting the sound of breaking glass. An advanced microprocessor processes information about the frequency, amplitude and timing of every sound. The Impaq Glass Break can be set to either Plate and Tempered or Laminated and Wired glass types. Dual green and red LEDs indicate pre-alarm signals. The Impaq Glass Break can be mounted on walls, in corners or on the ceiling.

An alarm system that has individual control access. Ideal for small homes or for use by the elderly and children as there are no access codes to remember.Solar siren uses daylight to maintain battery charge – reduces the need to buy expensive non-chargeable batteries. Once it detects an intruder through a door or window it sounds a 95db alarm

Wireless alarm with motion detection and remote alarm. Also suitable as door chime. Easy to operate and a quick installation without any wiring. Pre-programmed exit and entry delay. Perfect for securing any room or area. When it detects infrared-movement it sounds a 90db alarm .

Design briefJudging by the evidence I have collected I have come to the conclusion that there is a need for my product idea of a bath temperature alarm. The evidence I have collected tells me that there is a definite risk of a child being burned in a dangerously hot bath. The majority of the people who worry about this health risk are parents who have children who use a regular bath but need constant supervision around a bath. Using this conclusion my design will have to be a reliable way of alerting the user that their child’s bath water is dangerously hot or cold. Its input will have to be a thermal sensor that will be set to a specific temperature. The output could be some sort of visual indication of the temperature of the bath, propably LED based. my next step should be to find suitable circuits that match this design brief. I already know that the circuit I chose shouldn’t include a 555 latch switch as it is not suitable to a bath temperature alarm. To build my circuit I am using a block method where I amusing pre built component blocks to aid design and building my circuit. The resources I have:• Circuit wizard • Websites that specialize in circuit ideas• School recourses

Product analysis Bath Temperature & Water Level Alert Alarm

The Bath Level and Temperature thermometer can be used in the bathroom where care is required. It shows the water temperature with high/low alert feature. The Bath Level and Temperature Alert Alarm also includes a water overflow alarm system. Digital temperature display. Alarms if water temperature outside pre-set level.

Baby bath water Thermometer

The baby bath water temperature alarm feature a wireless thermometer connected to central hub which give more detailed data. Feature a temperature sensor with a high/low alarm feature. Sets off alarm if water is outside pre-set temperature.

Bath Temperature & Water Level Alert Alarm Baby bath water Thermometer

Function To alert parents when a babies bath is overflowing or too hot and to provide an accurate timer.

To provide parents with detailed information about the bath water and to alert them when it is too hot.

User need fulfilled

The user need is fulfilled as does alert the user when the bath water is too hot

The user need is fulfilled as It does alert the user when the bath water is too hot

Materials used in construction

Cheap plastcis propably used for the outer casing and a this clear plastic used for the LED display

The hub and wireless moniter is made from synthetic rubber and acrylic and a clear durable plastic used for the LED display.

Durability of product

The durability for this product is not likely to be very long as the cheap plastics used can be very easily broken.

The durability of this product is likely to be short as the materials used are cheap meaning they are not very sturdy, however the durable clear plastic used for the LED display could longate the life of this.

Sustainability (6Rs)

The exotic design of this product indicates the designers did not take in to account sustainability when designing the amount of materials needed during the designing stage as the have used more materials needed for looks rather than sustainability. The product is not recyclable.

The compact design of this product indicates that designers have attempted to reduce the amount of materials needed when creating it. The product is not recyclable and has no other features to make it reusable as something else and doesn't seem to be repairable by someone with little experience in electronics.

Life cycle Bought, used, not needed, thrown away. Bought, used, not needed, thrown away.

Energy use Uses 2 x AAA 1.5 Alkaline batteries size batteries Battery life: minimum 12 months

Hub: 2xAAA 1.5V Alkaline batteriesWireless thermometer: 1.5V 2xAA Alkaline batteriesBattery life: Minimum 12months

specificationThe purpose of my proposed product will be to alarm parents when their babies bath has become dangerously hot or cold, this to allow parents to feel that their babies bath is safe.My proposed product will need to sense the temperature of the bath water this is to determine whether the bath water is safe for a baby as many people agree the bath can be a dangerous placeMy proposed product will need to have a system of informing parents about the temperature of the bath, possibly and LED system as parents agreed that was a good idea.The power supply for my proposed product will need to be a 9v pp3 battery because that is the safest power source I can use for my proposed product also my product will need to be portable because using the mains around the bath would be dangerous and unpractical.My proposed product will run on 9v as that is what the power source will give out.My proposed circuit will not have an on/off switch this is to avoid the safety risk of forgetting to turn it on.My product will be designed using current products on the market to create a reliable product similar to those on the market.My proposed product will be manufactured by using computer aided design software to create the right size PCB board and then I will individually place and solder each component to the board this is to manufacture my product accurately and efficiently.

Delay before INPUT

INPUT Combine inputs?

Delay after INPUT PROCESS

Delay before OUTPUT

OUTPUT

instant Temperature sensor (cold)

And instant Transistor instant LED lights, probably colour coordinated, i.e. Blue=cold

4 seconds, to allow for user to place in bath correctly

Temperature sensor (hot)

none 1 second comparator 1 second Siren, could go on and off to maximise noticeability

Temperature sensor (just right)

Or 2 second Darlington pair 2 second Buzzer, as indication that the bath is dangerous

Multi range temperature sensor

3 second 3 second

I know that I am designing a Bath Temperature alarm designed for small children. I know the input will have to be a temperature sensor however I need to consider what other features I could use within my circuit, I know the output must be obvious to alert the parents as to whether there babies bath is dangerous.

4 circuit ideasHere are 4 circuit ideas I have found on the internet to base ideas for my circuits final production. Each one contains a description and a box diagram. When the resistance from the thermistor is low enough it forces the current through the transistor to the buzzer, this circuit is a very basic representation of what my interpretation of what my intended circuit is to be so I will not be considering this circuit for final production

This is a circuit I had made in a previous task in which I had to design an alarm that would sound when a baby’s temperature was too hot but I think I could repurpose it to work as a bath temperature alarm.

This is part of a circuit that I found. It was originally a bath temp and depth alarm but I am not including a depth alarm so I have made the adjustments accordingly.

Input

A thermistor that will send a signal when a certain temperature is met.

Process

A transistor to drive the light load of the buzzer output when a signal is received from the input

Output

A buzzer that will sound when a signal is received from the input and the process is driving it. This will alert the parents that the bath is too hot.

Input


Process

A Darlington pair to drive the load of the buzzer output when a signal is received from the input

Output


This is part of a circuit that I found. It was originally a bath temp and depth alarm but I am not including a depth alarm so I have made the adjustments accordingly.

Input


Process

A Darlington pair to drive the load of the buzzer output when a signal is received from the input

Output


In this circuit instead of a resistor there is a Darlington pair connected so when the resistance from the thermistor is low enough it forces the current through the Darlington pair towards the buzzer. Again this circuit is a very basic representation of what my intended circuit is to be and again I will not consider this for final production

This is another circuit I had found it latches on when set off and includes a reset button.

Input


Process

A thyristor to drive the output and latch on when a signal is received.

Output


In this circuit when the resistance form the thermistor is low enough it forces current to the thyristor towards the buzzer but then it recycles the current towards the buzzer until the circuit is reset using the switch. This circuit, like the ones before, is again a very basic representation including to much from my design brief so I will not consider it for final production.

This circuit is designed to have 3 LED lights to show what the temperature of the bath is.

RED= too hot (alarm will go off)

GREEN= just right

BLUE= too cold (alarm will go off)

Input


Process

Two operational amplifiers that will amplify the signal received from the input to drive two outputs

Output


Also there are 3 LED lights to inform the user about the temperature. The alarm will work in sync with this.

In this circuit there are comparators to drive the large amount of outputs happening. When the resistance from the thermistor is low enough it forces current to the right comparator and then it sends the current towards the right LED. This is a very good representation of what I intend for my final circuit to be as it contains everything included in my design brief, because of this, this design will be considered for final production.

Development of circuitThe 1st design:This as my original design of a simple heat detection. The led would turn on when it was too hot. When the resistance from the thermistor is low enough it forces the current through transistor towards the LED.

The 2nd design:This design was a little more complex as it incorporated 2 LED’s to indicate what the temperature was, either hot or not. When the resistance form the thermistor is low enough it forces current through the comparator and towards the positive LED. However when this is not happening current is forced through the negative LED.

The 3rd design:This design was almost identical to the previous one but this design incorporated a power indicator. When the resistance form the thermistor is high enough it forces current through the comparator and towards the positive LED. However when this is not happening current is forced through the negative LED.

The final design:This was my final design. I had gotten rid of the power indicator as I realised that the LED’s already told the user whether or not it was on. It has three LED’s to tell whether its too hot, just right or too cold. It is two of the above circuits combined. The variable resistors can be used to adjust the temperature at which LED will turn on. When the resistance form the thermistor is low enough it forces current through the comparator and towards the red LED(too hot). However when this is not happening current is forced through the blue LED(too cold). How ever also in this circuit is a set “in the middle temperature” at which a green LED will be switched on(just right).

Test table Test Expected Out Come Actuall Outcome Result

Led will apear when turned on

Any one of the LEDS will turn on when the circuit is plugged in and turned in

The green Led lights up

It works

Led will change when placed in water

LED will change colour due to temperature change.

The red blue lights up

It works

Led colour will acurately represent temperature.

If it is hot the LED will be red, if it is cold the LED will be blue, if it is warm it will be green

The red matches 35+ degreesThe green matches 26-35degreesThe blue matches 26- degrees

It works

PCB design:I had to go through over 4 different designs before arranging my components in a practical way that still allows the circuit to function. I have tested each step to ensure the circuit works all the way through. I first had to ensure all routes were connected by ensuring there was no blue and green wires. I had to also adjust the tracks and certain pad sizes to ensure that my circuit did not produce as much waste and have an environmental impact and also for neatness.

Name Symbol Image Function

100K Potentiometer A resistor with the ability for the user to be able to adjust the resistance

10k Potentiometer A resistor with the ability for the user to be able to adjust the resistance

10kresistor A device that resists the flow of electricity in a circuit.

1k resistor A device that resists the flow of electricity in a circuit.



Blue LED When a charge passes through this device it lights up.

Green LED When a charge passes through this device it lights up.

Red LED When a charge passes through this device it lights up.

2x operational amplifier Takes a weak signal and converts it to a strong signal

thermistor Increases resistance in low temperature and lowers resistance in high temperatures

Final PCB design

Battery (9v)

resistors

Thermistor

Comparator

LED’s

Variable Resistors

Testing Plan Test Expected Out Come Actuall Outcome Result



The green Led lights up

It works



The blue Led lights up

It works

Led colour will acurately represent temperature.



It works

Process Description Equipment Needed Safety Issues Tips For Success

Design PCB and Mask Circuit wizard none Remember to test designsRemember to adjust labels soit is easier to assemble

Sizing the Board Band Saw •Do not put limbs near saw when on •Remember to measure out lengths before cutting•Remember to wear goggles

Expose PCB to UV PCBMaskUV light

•UV light may damage eyes •Wear goggles

Develop Exposed PCB Development fluid •Development fluid can stain clothes and skin

•Wear goggles and gloves

Etch PCB Etch tankEtchant

•Etchant can be irritant to skin Wear goggles and gloves

Drill Holes DrillDrill press

•Do not put limbs near drill bit when on •Ensure drill guard is down and have small hole to ensure accuracy

Solder Chip Socket PCB Soldering EquipmentCircuit Clip Board

•Fumes can be dangerous and can burn skin

•Ensure none of the legs are joined together by solder

Solder Resistors PCB Soldering EquipmentCircuit Clip Board


•Ensure the right value resistor is in he right place

Solder Transistors PCB Soldering EquipmentCircuit Clip Board


•Ensure the legs are the right way round

Solder Off board Components PCB Soldering EquipmentCircuit Clip Board


•Ensure wires are right way round (i.e. Red is positive)

Shrink Wrap Connections Between Off board Components And Wires

PCB Soldering EquipmentCircuit Clip Board


• Ensure the shrink wrap covers the visible wire

Add Chip To Socket. PCB •If the chip is the wrong way round it could damage it

•Ensure the chip is fully in.

Here is my PCB board ready for the components to be soldered on too. After designing my PCB mask on circuit wizard I used a band saw to size my board, after doing this I then exposed it to UV light after being exposed it was then developed using development fluid which was then etch using etchant once this was finished the holes were then drilled into the PCB after having tiny holes to centre the drill.

Here is my PCB board and the printout of my circuit to ensure I solder the correct components in the right place. By doing this I ensured that there could be no error in the production of my PCB, as you can see the printout is orientated in the same way as my board to ensure I understand where each component should go.

Here is my PCB board and my resistors, the first of my components to be soldered onto the board. As you can see to solder something correctly you must first place the solder around the joint you wish to secure then apply the hot tip of the soldering iron to the solder ensuring a small blob is around the joint with no gaps, by doing this you ensure the joint is secured correctly.

Here is the correction of the mistake I made, by separating those two pins that were connected, I used a combination of the solder sucker to get most of it out I then used a copper wire to get the rest, I then had to re-solder the joint correctly.

Here is a mistake a made, I have soldered two chip pins together if left uncorrected this could cause serious problems for my circuit and could potentially blow the chip which could be a serious health hazard, there are several tools that could correct this mistake, the first would be a solder sucker which sucks melted solder off the PCB, the next is a copper wire which when heated will remove the solder as it sticks to it when melted.

Here is my complete circuit, as you can see all my off board components are soldered on, 3 LEDs, thermistor, slider switch and a battery clip, each off board component is soldered and then a small section of plastic tube is place around exposed wire, when heat is applied to this plastic it shrinks, forming a seal on these expose wires.

For the purposes of this demonstration, although my test says the thermistor should be placed in water to simulate temperature change, I have used a can of deodorant to simulate temperature change.

Testing Plan Test Expected Out Come Actuall Outcome Result



The green LED lights up

It works



The blue LED lights up

It works

Led colour will acurately represent Temperature.



It works

Description of Process What went well Problems encountered/changes made

Action taken to deal with problem

Design PCB and create mask

Board was shrunk to save materials

Auto-routing had not correctly mapped tracks completely

Had to manually map tracks

Cut board to size Using the band saw to cut my board to the right size

None none

Expose Mask and photoPCB to UV

Was exposed for the correct time

none none

Develop exposed PCB It was developed correctly

None none

Etch PCB It was etched correctly None none

Drill holes in solder pads Holes where accurate weren’t out of place

none none

Add resistors Correct value resistors were placed in the right places

Solder on certain joints were not complete (structurally unstable)

More solder was applied to ensure joint was fitted correctly

Add Chip socket Chip socket was applied in correct direction

Holes were too small for chip legs to fit

Holes were made bigger by using bigger drill bit

Add off board components Each off board component was soldered in and vacuum sealed

The negative and positive wires of the battery clip were the wrong way round

Both wires were swapped and soldered

Add chip to socket Chip fitted into the holder correctly

Chip would not work with circuit

Chip was replaced with previously tested chip ensuring it worked.

ImprovementsWhat could I have done differently:• One improvement could be to decrease the amount wasted by bringing my

components closer together.• I could have designed the circuit differently and instead of using an LED system I could

have used an alarm to indicate when the bath was dangerously cold or dangerously hot although this circuit would not be as user friendly as my current design.

D&T: Electronics and Control Systems Unit A511: Introduction to designing and making

Documents

intended user

regular bath

bath temperature alarm

childs bath water

intended product

child safety

security problem

problem of household