D&T Electronics and Control Systems

1. D&T Electronics and Control Systems By Harry Holmes

2. The theme of the project is generally based upon “Security,” and to evaluate different alternatives and forms of security. The spider diagram displays security related products. I have chosen the theme security as the primary theme because by exploring different categories of security product, effectively I can choose the most appropriate product that delivers the what it’s intended purposes are. In this case offering protection, hopefully the developed product will be able to offer some sense of security.

3. What The circuit will consist of pressure sensors that detect and triggers when an application of pressure is identified, possibly containing a time delay otherwise any form of contact will trigger the alarm, putting into mind its practicality. Where The pressure alarm will probably be placed at possible points of entrance in the burglar’s perspective, for example windows and doors, furthermore, the entire circuit can be concealed as a doormat therefore it is less suspicious and interfering. When During a robbery, a burglar might try to enter the premises. In this situation if the house is secured then it will most likely be a trigger an alarm and potentially prevent further intrusion. Equally, if the house is insecure than there are no obstructions restricting the burglar’s attempts to steal. USER NEEDS Why The purpose of security produces are to certify the consumer of protection or promoting the sense of security. Subsequently preventing crimes of theft and burglary. Who The product will generally be used for protecting items and possessions against prospects of burglary. As a result presenting a level of reassurance towards homeowners.

4. According to statistics from the British Crime Survey (BCS) Burglaries in England and Wales have increased by 14%. Recent survey on 45 000 households have also shown that crime rates has escalated slightly.

5. Questionnaire

6. Questionnaire Result (Qualitative Data 1) • Conclusion • The questionnaire and the market trend of similar products will be used to determine the product’s specification. • The majority of people said that their houses are insured therefore there may be less need for a burglar alarm however, 20% of people said that they weren’t insured. As a result there may also be a need for burglar alarms. • The question asks whether using pressure switches in an alarm is practical, two-thirds of people said yes. So it would probably be sensible to add pressure sensors in my circuit. • Most people decided that the product should be sustainable, in order to achieve sustainability products will need to use less energy and resources. Such as using renewable energy, recyclable materials, changes to the manufacturing process, etc… • Almost everyone said that they had neighbours, in this case alarms with sound would be more effective because burglars will feel more uncomfortable breaking into a neighbourhood as opposed to an isolated house. Consequently a siren will have a greater chance of deterring the intruder as the sound of a siren may alert the people in the area.. Which also means that a time restriction should be fitted in the circuit, this is because the sound of an alarm may disturb people in the area. • Although most of the homes are insured two-thirds said that they expresses a need for an alarm. This may be because irreplaceable items such as photo albums cannot be compensated. So there is a need for burglar alarms despite most houses being insured. • Most people said that it should be portable. The obvious choice would be batteries, however there is also a requirement for the product to be sustainable. Using batteries may harm the environment if it is not properly disposed. For that reason we could use rechargeable batteries.

7. Questionnaire Result (Qualitative Data 2) I have chosen sound as the output of my circuit because it was selected by the most amount of people. Also because light is simply too hard to detect especially when someone is asleep. Some suggested sound and light, but if you were close enough to see the light being activated then surely you will also be able to sense the sound. For that reason I don’t think two separate outputs (light and sound) will need to be combined. Most people chose batteries when asked what power source they wish the circuit should operate on. Nonetheless plugs can also allow the circuit to be portable. Furthermore it is much more sustainable than disposable batteries, and also more reliable because you won’t have to worry about whether the batteries have run out or not. Thus excluding the need of a power indicator, resulting in less resources used and reduces the cost and energy of the manufacturing process. Which is being sustainable and environmentally aware. Meanwhile, solar powered alarms may be expensive to make and therefore expensive to buy. Solar powered devices only work when there is enough light, however the alarm will be placed indoors. On the other hand there might not be a plug socket near the entrance of the building, so the alarm may not be as effective. If there are no plug sockets then it could use cables, however those cables will also need to be manufactured. Additionally it may interfere with everyday lives. So I have chosen to use batteries to power my circuit.

8. Questionnaire Result (Quantitative Data) The price that was chosen the most was £21-£30, this shows that my product will need to be below £21 in order to make a profit but also match the buyer’s expectations. Because most have gone for the intermediate price range, so the alarm will need to be more complex than a simple circuit meanwhile not above the cost of £21. If there is a need for alarms, (which there is because two-thirds of people said that they expressed a need for an alarm) then maybe people will be prepared to pay £30 for a household alarm. So the product could be made with better quality materials or with improvements to the circuit. To find whether there is actually a need for a circuit alarm I asked a more subtle question ,“How many times a week is your house unoccupied.” I thought that it was an important question because in question 5 which asks whether people expressed a need for an alarm, most people said yes. But this could be because the alarm gives an added sense of security. So why not just build a circuit where there’s only a flashing LED? Which saves expenses and resources . By asking this question, it identified that there is a genuine need for an alarm because most people leave the house unoccupied for 6 or more time a week. So there is a need for a proper alarm that can actually deter a burglar once that person once entered the house, not just to reassure people. Since there are a lot of times a house is unoccupied, it would be wise to have the alarm on at all times. So using rechargeable batteries are probably a good idea.

10. LED garden light - Amazon The product is a garden light equipped with 30 separate LED lights. It draws its power through the plug socket. The recording camera is capable of recording coloured images during daytime and records black and white images at night. The 380 resolution camera requires a 12V power supply. Its manufactures are “BV&Jo” Alarm Panel - It has a built in tamper control in order to prevent any unauthorised modifications. There are also 2 variations of keypad LCD and LED. The LCD keypad is capable of supporting 250 event records such as the time and date of interactions with the panel, where as the LED holds 8 event memory. Its battery capacity is 2.4Ah. The manufacturer of this product is “Honeywell.” Surveillance Camera - The security camera records images up to 550 TV Lines or More. The camera also blocks strong light sources improving its overall video quality and prevents burglars from disabling the camera by shining a bright light. It requires a AC 24V ±10% /DC 12V power source and it’s power consumption is approximately 3W. The manufacturer is “Honeywell.”

11. Through researching 3 similar products on the market I found out that most would not interfere with everyday lives. However it isn’t so simple when using a pressure alarm because it will not recognise whether the owner has stepped on it or if it’s the burglar. Therefore it will still be triggered regardless of who stepped on it in the first place. To solve this problem I’ve decide to place a SPST switch near the power source so that it can be manually turned off. Since the pressure sensors can be concealed under a mat so anyone could step over the sensors without triggering the alarm. Product Analyses and Summary

13. System Diagram

14. Systems Descriptions Process The 555 chip is used in basic timer devices. The mono-stable has 2 states. One of which is stable and the other unstable (transient). Once activated the mono-stable will become “unstable.” After a set amount of time it will then return to its normal “stable” state. This is particularly useful when you’re creating a time period in response to an input. Length of time can be adjusted using the variable resistor. Power source The circuit will be power by two 4.5 v batteries. In total supplying 9 volts. Input This is an inverted push to make switch. Because I intend to have a pressure switch before the mono-stable. So I need to have a negative output to trigger the mono-stable. Which is why the pressure switch and the resistor have been swapped. Logic Gate (AND) The AND gate bonds 2 inputs so that you can have 2 separate triggers. The AND gate needs both inputs to be high to turn on the output.

15. Process The MOSFET is more sensitive than the Darlington Pair or the transistor because it has a higher gain. When using logic gates in a circuit, it is sensible to use something sensitive to act as a drive. Process A buzzer is a device that emits sound. It is often used to notify people of something. Output This is a LED, but it requires a negative output to turn it on. Light Dependant Resistors LEDs are more efficient in the way of producing light compared with incandescent bulbs, because it converts more electric energy into light rather than heat energy. Compared with ordinary bulbs, LEDs also have a longer life expectancy, are smaller, and less easy to break. However, larger LEDs can be more expensive than normal light bulbs. Input This is an SPST switch, once it has been pushed it makes a closed circuit allowing a current to pass. It needs to be manually re-opened to break the current flow.

20. INPUT Phase 1: When the Piezo fragment has been displaced through movement, it generates minute currents detectable by the Mosfet. PROCESS Phase 2: The Mosfet then enhances (amplifies) the current initially produced by agitating the Piezo crystal (PZ1) , which in this case is the input that senses vibrations. PROCESS Phase 3: The current then reaches the 555 timer, indicating that the duration in which the circuit output is active has been lengthened. OUTPUT Phase 4:The output is a Piezo sounder which releases sound when electricity is applied. However, burglar alarms are less likely to need Piezo sounders because it only needs to product a sound in order to “alarm” the burglar. Therefore a buzzer or siren will suffice. This circuit could solve the problem though using Piezo crystals which produces a charge depending on how much the crystal is deformed. Therefore does not require additional power sources. However the Piezo crystal can pick up background sound or voltage that may inadvertently trigger the alarm. Furthermore, the piezo crystals are predisposed to cracking when under strain.

21. POWER SUPPLY/INPUT Phase 1: The power supply is presented as 9v batteries. The pressure switch allows current to pass when pressed. INPUT Phase 2: Push to make switch moderating current flow. PROCESS Phase 3: The Darlington pair transmits a “load ” that drives the output. The thyristor “latches” to the circuit when the circuit is activated. OUTPUT Phase 4: The outputs are the lamp and buzzer which are integrated to emit luminosity and sound. Moreover, producing light and sound as an output was chosen second in favour in the questionnaire; the first being sound. The circuit has 2 outputs lamp and the buzzer. What emits sound and light, allowing it to be useful at night. However, it is a latched circuit therefore it has to be manually turned off. Which would be more problematic especially as there are no on off switches besides the power supply.

22. a INPUT/OUTPUT Phase 1: An open and close switch that can be manually closed or opened to control the circulation of electricity. Along with a power indicator that displays the state of the power supply. OUTPUT Phase 5: The buzzer acts as an output, emitting sound in order to frighten and deter the burglar. b INPUT Phase 2: Push to make switch substituting a pressure switch LOGIC/PROCESS Phase 4: The logic gate (AND) incorporates both inputs into the circuit along with a Mosfet to amplify the current. Furthermore, the Mosfet is very sensitive, making it suitable as a burglar alarm because it reacts to the inputs faster than a transistor or Darlington pair. PROCESS Phase 3: The monostables used to extend the duration in which the output is on. This circuit has combined 2 inputs. The first input (a) will be place in the perimeter of the building and the second (b) will be based inside. Primarily because he burglar will recognize that the building is protected as he steps on (a), the light will activate. However I should replace the LED’S with lamps and the buzzer replaced with a siren in order to make the outputs obvious.

23. Final circuit Video * LED substituting a lamp ** The buzzer represents the siren

24. Buzzer acting as a siren. PCB Format after converting the original circuit design. The LED acting as a power indicator. Which also gives the user a sense of security as it shows that the circuit is operational. Both Push to Make switches represents pressure mats.

25. Circuit Evaluation Problems I stumbled upon some problems when converting my chosen circuit into a PCB. Firstly, because it was too complicated the program was only able to route 83% (at best) of the circuit. This was mainly due to the over-complicated circuit as it had 3 separate chips (2 mono-stable and a logic chip). Furthermore the converted PCB had 6 flying wires (Blue wires as show on the video) along with 7unattached tracks (lines are shown in green). Eventually the components were repositioned connecting all the previously unconnected tracks. However, there were more flying wires and the circuit(s) did not work, the pressure sensor worked but the buzzer did not sound when both pressure switches were triggered (The LEDs shows that the pressure switches was activated). This prompted me to redesign my circuit so that it still had a time delay and 2 separate inputs while cutting back on its complexity. Automatic routing after converting the circuit into a PCB format Video evidence of my circuit not working.

26. Simplified Version of the Circuit • Getting rid of the 555 timer has made the circuit: • Simpler and therefore easier to manufacture. • Cost efficient as less materials are used. • Environmental because there are fewer components. Components that may have harmed the environment during its making. The circuit allows the user to adjust the time setting in which the siren is on for, without needing two monostables. The variable resistor (when is set at above135K) will turn itself off just after the capacitor stops producing a current. So in this case input x should turn off after input y. Since it is an AND gate, an input of 0 on any one of its legs will immediately silence the siren. All in all, it gives the user an option to adjust the time setting according to their needs. Resistor to protect LED a x Variable resistor allows user to adjust resistance, and the amount of time input x is positive. y Without the monostable in the way, I was able to place the pressure switch directly in line with the capacitor. This save more space when it comes to making the circuit. b The main adjustment in this circuit was getting rid of the 555 timer that was placed with input b earlier. The capacitor offers a delay by storing electric energy and releasing it when needed (e.g. pressing the push button switch). The capacitor behaves like a battery, however, it is smaller, quicker to recharge, and releases its energy quicker (less than a second). This makes it appropriate in a burglar alarm as it can recharge quickly in case the burglar returns, and because of its sensitivity, able to respond quickly when the circuit is triggered. I have also added some resistors which was not included the previous circuit diagram (slide 22). “Circuit Wizard” allows for the some components to be placed without resistors. When running a simulation program, the circuit worked without any difficulties, and meet its designed purpose. However, in reality, the circuit would not have run as smoothly if there was no resistors put in. The LEDS, for example, should be protected with a resistor to prevent it from being damaged or short-circuited.

27. Picture 1 After a successful conversion of the final circuit diagram to its PCB layout, I was only meet with four “rats nests,” which are green wires shown in the image. The green wires show that there are missing routes between the respective components. This problem cannot go unnoticed as a circuit will not work with missing connections. The only way to solve this is to either arrange components so that there is a alternative route for connection, or, to connect a “flying wire,” that links the two points separately, with a cable that crosses over existing routes. All inputs (all off bard components) have been placed on the right hand side. This makes it easier for others to understand the circuit because people would usually “read” the circuit from left to right. So components should be placed in the order of (from left to right) power, input, process, and output. This would make the circuit neater, and the manufacturing process easier as it gives a faint idea where various components belong. By placing all off board components outside, there is also less risk of wires getting in the way of other components, making it easier to solder other components, furthermore, making it easier when handling the circuit. It also means that wires do not have to be as long. This reduces materials used, creating a more sustainable circuit. Although most unconnected routes have been fixed, one still remain. It would be difficult to get rid of this particular “rat nest” without disturbing other components, and therefore creating more “rats nests” during the process. A flying wire offers a simpler solution, but should always be used as a last resort because it make the circuit untidy. Picture 2 Flying wire

28. Picture 3 As there are no more unconnected wires, I can now work on the tracks. Most of the tracks run vertically and horizontally. There needs to be spacing between components so that when it comes to soldering, there is enough room. It also makes the tracks easier to etch. Picture 4 The PCB has been made smaller by tidying up the tracks. By making it smaller allows the alarm to be concealed, it also saves materials. • PCB Specifications • Standard Track Width: All track width are to be set at 0.04 inch. Increasing the width of the tracks means that it requires less etching, it also make the track more resilient. It is common during manufacturing and soldering that the tracks get scratched. A wider track makes is less vulnerable to occasional scratches. • Pad size : All round pads should have a 0.12 inch diameter and holes in the centre of the pads should be 0.01 inches in diameter. Larger pads allow more surface molten solder can attach to. This make the component more secure. If too much solder is applied, bigger pads may be able to hold some of the solder so that it does not “spill” onto other pads or tracks. • Oval Pad size: Hole sizes for oval pads should also be 0.01. Everything else unchanged. Having a small hole in the centre of pads helps when drilling because it acts as a starter-hole, which can then be made larger to fit different components.

29. Testing of PCB The video is a working example of the circuit. The sirens sounds when both inputs are triggered, it also continues to make a sound, eventually turning itself off. Notice how the red LED stays on after the siren has stopped. This time difference allows the user to adjust the variable resistor so that both inputs are positive for a shorter amount of time. This should reduce the duration the siren in on. However, there is a limit on how much charge the capacitor can hold. So the circuit will turn itself off once the capacitor looses it charge. The time restriction on the capacitor in constant, but the length in which the output is on can be changed. If the user wants to increase the time in which the siren is on, they could simply increase the resistance on the variable resistor so that one input will turn off before the other. But as mentioned earlier, there is a time restraint on the capacitor that cannot be changed. So the circuit will turn itself off eventually.

30. Picture 5 After testing that the PCB works, I removed all the terminal blocks. Terminal block are not crucial in this particular circuit as they are bulky. Terminal blocks like other on-board components need to be directly soldered onto the PCB. Afterwards, a short length of insulation will need to be striped from the wires which connects the terminal blocks with various off-board components. The exposed wires will then be secured onto the blocks by fastening it using a screw. Replacing the connecters with pads will mean less materials used, and possibly saving time and effort. Also, using terminal blocks ensure that wires are protected from conducting materials which may cause damage to the circuit. Picture 6 Most labels have been removed leaving the ones that show the components value and name tag.

31. 2 Seconds SPST switch is turned on. The power indicator (green LED) lights up. 3 Seconds Pressure switch 1 is triggered. As a result, the red LED turns on, indicating that input 1 has been activated. 5 seconds Pressure switch 2 is triggered. As input 1 is also on, the buzzer is turned on. 11 seconds The buzzer turns off, so does the red LED. However, the input 1continues to supply a current (shown by the glowing LED). Because there’s an AND gate between the inputs and buzzer, it won’t make a difference. The buzzer remains off. 19 seconds The red LED turns off.

32. PCB board after being etched. The photo shows the underside of the PCB. There are some placed where I will need to take caution when soldering, places where there are exposed copper and PCB. This photo show me putting on a LED. When attaching components, make sure it is flat on the board so that there are no exposed legs which may be vulnerable to corrosion or being short circuited. To make sure that components lie flat on the PCB: Put both legs through the correct holes. Once they are through, bend both the legs so that the component does not fall out. Check if the component is flat on the other side. Secure the entire circuit board onto a clamp. Solder with one hand using the soldering iron and the other supplying solder.

33. It is practice to label the PCB with the respective values of its components. This makes it easier when it comes to soldering. You no longer have to refer to the circuit diagram when placing components. Furthermore, resistor values in particular should be checked before being placed onto the board. By going through and checking components systematically, it minimises mistakes made while soldering. The resistance chart shows the values on a resistor based on its color-coding. Solder groups of components one at a time. All resistors have been soldered onto the board before moving on to different components. The reason for this is because it’s easier to find similar components than to pick out components at random. Also, it gives a chance to practice soldering that particular type of component, so therefore the quality of soldering improves.

34. Some of the solder joints are slightly tilted, this was because I bent the legs of the component outwards in order to prevent it from falling off while soldering. The top of my circuit All the resistors have been soldered flat onto the board. All resistance values have been checked, all were correct. The chip socket has also been soldered correctly as there is an upper dent, which faces in the right direction.

35. How I solved the problem Adding too much solder meant that the solder merged itself with another solder joint, making a connection with the neighbouring pad. This connection have to be removed, otherwise it will cause it to short-circuit. I ran the solder in-between the connected pads. This re-melted the solder and I was able to remove the excess solder cleaning. The grey-green smudge left behind can be easily scraped, making the circuit neater.

36. Flowchart Test The circuit is not working properly, check for any faults in the connections. START Connect the circuit with an off-board battery. Then switch on the SPST switch. does the green indicator turn on, and stay on permanently as long as the power is on? Are all the components in the correct place? Press either one of the pressure mats, does the siren sound? Yes Yes Yes No No It is most likely the off-board component. Check if the negative and positive wires are the right way round. The circuit will not work, make sure all components are in the right place. No Press the second pressure mat, does a red Led light up. Yes Check the circuit, then retest. When both pressure mats have been triggered, does the siren sound? No Does the siren turn off just when the red LED turns off? Yes No The red LED indicator on the monstable is not working. Check if the LED is the right way round. Yes No Retest the circuit, does it continue to work? There may be a defect in the siren, test it after the circuit has been thoroughly examined. Finish Yes