Design Specifications
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AIR's purpose is to help make the daily lives of the user less stressful by reminding them of which items they need to bring with them. AIR has been designed so that it can be reconfigured to the user's desired profiles. This means that the user may change which items are required for the various activities.
In the current design (which may be open to change). This is achieved by implementing DIP switches (dual in-line package). Each input line into the dip switch has its own connection to each of the activity list triggers. AIR will be using 16 pin 8 way DIP switches as seen below in Figure 1. Each option within the ‘item list' will have its own dedicated pair of DIP switches for simple reconfiguration. Simply, if an item is required for a certain activity, the appropriate input line is moved to the ‘on' position. The use of DIP switches does increase the wiring complexity of AIRs circuitry, though this is offset by the fact that now AIR is completely reconfigurable and also that a new circuit design does not need to be created for each person and their personal profiles.
Figure 1 - 8 Way DIP Switch
AIR is powered by a simple DC adapter that will output 15V. The adapter comes at a reasonable cost and removes the need to build a customer power supply significantly reducing costs.
Figure 2 – 12V DC Adapter
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Figure 3 - LED 5mm Red ..................Figure 4 – Red LED Illuminated switch
Light Emitting Diodes (LEDs) will be used as indicators on the device. These will be used to inform whether the unit is powered, which items are needed or whether or not the motion sensor is enabled. LEDs generate little to no heat, are inexpensive and have extensive lifetimes. Red LEDs have been chosen as seen in Figure 3. Momentary switches will be used for the main interface of the device. The item list will incorporate a joint LED and switch in a single package (Figure 4). This was chosen as to easily distinguish which items are needed and which have been checked off. (See Appendix 3 for technical specifications)
Flip Flops have been chosen to provide control over each items indicator LED and their associated activity. D flip flops have been chosen to provide this control. The widely available Texas Instruments 74LS74 dual D flip flop IC (integrated circuit) has been chosen. The 74LS74 IC contains two D flip flops and also includes Set and Reset lines. These ICs come at a low cost, are half the cost of the previously used JK flip flop ICs and can be configured in such a way to provide the exact same function.
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Figure 5 – Texas Instruments 74LS74 ...................Figure 6 – 74LS74 Pin Layout
Each activity input will pass through the DIP switches (if activated) and then trigger the set line of the D flip flop. This then sets the ‘Q' output line to active. Once the line is active, LEDs connected to these output lines will activate indicating which items the user needs. When the user has determined they have the required item, they press the associated ‘check' switch, this will toggle the flip flop at its clock input. The D flip flops have been wired and connected in such a way that when the clock input receives a toggle, like that from a momentary switch, it will cause the output line to be disabled causing the LED to switch off. (See Appendix 4 for 74LS74 datasheet)
If the user has made a mistake, or simply wishes to recheck they have all their required items, they may simply press the ‘Reset' button to restart. The reset button is connected to each D flip flops reset input. Once an input from the reset line is received it causes the ‘Q' output line to be disabled, switching off the LED. Alternatively if the user has selected the wrong activity from the list, simply selecting another one will automatically activate the required LEDs and disable the ones not needed.
Figure 7 – LM35 Precision Centigrade Sensor
An LED is being used to indicate a temperature warning to the user, that is, if the temperature is too low it will activate warning the user that appropriate clothing might be necessary. The LM35 precision IC has been chosen for its low cost, accuracy, and ease of use. The LM35 sensor self heating causes a less than 0.1 o C temperature rise in the surrounding air. The sensor increases its output voltage by 0.1V/ o C, e.g. 21 o C would mean the LM35 outputs 0.21V. The sensor will be placed appropriately in a special protective compartment that will be placed outside of the user's home. (See Appendix 5 for LM35 Datasheet)
The main circuit design has been created and can be seen by proceeding through the following link. The circuit design excludes the LM35 temperature sensor circuit and the motion sensor circuit.
Click here for circuit diagram.
The motion sensor is the primary trigger for the AIR, a Passive Infrared sensor will be used (PIR). The PIR sensor will be placed in a non-obtrusive location, such as at the corner of a ceiling. It will be aimed at an angle that will be enough to cover a small area, such as the entrance to a home and near the AIR device itself. This angle will be mainly determined by the height of the ceiling where the device is being installed. It runs off a 9-16V supply, which is compatible with supply for the internal circuitry of the control unit. It provides ease of installation in integration with AIR.
The PIR has three wired connections, a positive terminal, ground and an output line. The device itself is basically a normally closed switch. When powered, the sensor emits a steady current in the normal state. When motion is detected, the control line contact will open and the current flow will stop. Therefore appropriate circuitry in AIR is required to interpret this loss of a signal as a trigger to activate the entire device. (See Appendix 6 for more details)
Figure 8 – PIR Motion Sensor
To integrate the PIR sensor into the circuit AIR will be using a 555 timer IC. The 555 timer can be easily configured to behave in an ‘astable' or ‘monostable' modes. The astable mode means the 555 timer will emit pulses when triggered, monostable mode means that the timer will emit a signal for a set period of time. Monostable mode will be being used, this is as the PIR sensor will trigger the 555 timer which will then activate its output for a set period of time. This has been chosen to be between 3-5 minutes. This will allow operation of the panel of the AIR for an adequate time, before restoring it to standby. This will reduce the overall power consumption of the AIR and is important in the modern world of climate and energy aware customers. Once the 555 timer is triggered it will then simple be connected to a transistor that will allow power to flow through AIR.
Figure 9 – 555 Timer IC
A helpful feature of this timer is that if the user triggers the motion sensor and uses the AIR, it will not disable the device after the allotted time period since the user will still be constantly triggering the PIR sensor while using the AIR. What determines the output time of the 555 timer is the values of capacitors and resistors that are connected to it. It is also the manner in which these components are connected to the 555 timer that determine whether it is in astable, or monostable mode. In monostable mode to determine an approximate output time, the following equation is used.
T = 1.1 x RC
T = Time (Seconds)
R = Resistance (Ohms)
C = Capacitance (Farads)
The following circuit diagram is how the 555 timer is configured to operate in monostable mode. To adjust the output time instead of customising the device for each setting, a potentiometer (manually adjustable resistor) will be used so that the user can vary the time period to their own requirements.
Figure 10 – 555 Timer test Circuit (LED represents AIR being powered)
AIR will also use a piezo buzzer in conjunction with another 555 timer. The piezo buzzer can be connected to the output and this will create an alarm, for use in the event of the user leaving the house without completing the use of the AIR. This buzzer circuitry would be triggered by a 555 in monostable mode, set for, say, four seconds. Economies of scale can be realised by using a 556 timer in lieu of two 555 timers. This will lead to more usable space on the circuit board due to fewer IC packages being used.
Richard O'Connor - 3282570 (1400 words)
Michael Panich, 3117662. (321 words)
1 - 8 Way DIL Switch - 16 Pin DIL PACKAGE
Features:
- End stackable
- Moulded 0.3" IC packing outline for automatic insertion
- Smaller sized
- Twin contact design
- Gold plated contact and tin plated terminals.
- Switching: 25mA 24VDC
- Non-Switching: 100mA 50VDC
- Contact Resistance: Initial 50mmax
- Dielectric Strength: 500VDC min 1 minute
2 - 12V DC Adapter
-Dimensions; 160(L) x 85 (W) x 40 (H)mm
-Input: 220 - 240VAC
-Output: 12VDC @ 5 Amps total
-Input Lead Lengths: 1.2m
-Output Lead Lengths: 1.8m
-Termination: 2 pin connector
-Green LED power indicator
3 - LED 5mm Red 15mcd
-Emitted colour: red
-Lens colour: diffused
-Wave length: 697
-nm: 90
-Pd W: 45nW
-If mA: 15
-If mA (peak): 50
-Min: 1.7
-Vf (V) Typ: 2.1
-Max: 2.8
-IV Min: 2.5
-MCD Typ: 10
-Viewing Angle: 36
4 - 74LS74 Datasheet
5 - LM35 Precision Centigrade Temperature Censor
6 - PIR Motion Sensor
Features
-100 Degree Field of View
-Intelligent Pulse Count
-15m coverage
-Simple Installation
Specifications
-Dual Element Sensor
-9-16VDC operating Voltage
-13mA current Draw
-N.C contacts
-Selectable Pulse count 2-3
-Tamper switch
-Walk Test LED
-RFI immunity Ave. 30V/m (10-1000MHz)
-Detectable speed range 0.3 - 1.5m/sec
-Dimensions 100(H) x 60(W) x 40(D)mm
7 - 555 Timer Datasheet