Transmission Basics: Beginners Guide To Antenna Design

Antenna design begins by understanding your transmission requirements. You need to know the wavelength / frequency of the signal for the antenna, before beginning work on antenna design. The next step is understanding the antenna type that would suit your application. Moreover certain applications would require several antenna and this may cause a confusion for novices.

List of currently used antennas

• Mono pole Antenna                                          
• Helical Antenna
• Log-Periodic Dipole
• Dipole Antenna 
• Yagi-Uda 
• Slot Antenna
• Short-Dipole
• Spiral Antenna 
• Cavity-Backed Slot
• Half-wave dipole 
• Corner Reflector 
• Horn Antenna
• Broadband Dipole 
• Parabolic Reflector 
• Vivaldi Antenna
• Folded Dipole 
• Microstrip patch 
• Slotted Waveguide
• Loop Antenna 
• Planar Inverted-F 
• Inverted-F
• Cloverleaf Antenna 
• Bow-Tie 
• Antenna in wearables

Parameters in Antenna Design

All of these and more are being used in some or the other application around us. However designing any of them would involve understanding parameters and suitability for a particular application. Some parameters involved with antenna design besides basic aesthetics are the antenna resonance point or the operating frequency, and the antenna bandwidth or the range of frequencies over which this antenna would be expected to operate.

RF antenna consists of capacities and inductive components in it’s design. Hence this calls for tuning between the two. This brings in a resonance point into the picture. You might be familiar with the relation between capacitance and inductance in tank circuits

The values of inductance and capacitance in the circuit, we can tune the circuit to receive a particular frequency. This may sound simplistic in reality, practical implementation, shows that a circuit tuned at a particular frequency receives a range of frequencies. This brings in another factor the range of operation for the antenna.

RF antennas operate up-to a certain range of frequencies about the resonant frequency. This becomes a necessity, as the signal transmitted at a particular frequency would undergo several modifications, during its travel. This allows a range of frequencies to pass through, but outside the range the reactance rises to levels that are often too high for satisfactory operation. Other characteristics of the antenna may also suffer due to the increased range of frequencies hence the tank circuit filters the frequencies about the central operating frequency.

Impedance Bandwidth
The impedance of an RF antenna stays same and does not change with its frequency. This causes an increase in the amount of reflected power. In case of a transmitting antenna, beyond a given level of reflected power, damage may occur to either the transmitter or the feeder. This would be a significant factor limiting the operating bandwidth of an antenna but not so much on the reception end.

The impedance changes of the antenna are not as critical as it will mean that the signal transfer from the antenna itself to the feeder is reduced and will cause the efficiency to fall.

Daytime Running Lights Controller

The circuit presented here is to activate DRLs on any lighting that uses LED and/or incandescent bulb in a vehicle. Before attempting to construct this circuit, remember that, you cannot directly hook up the circuit to any circuit that is controlled by the CANbus system in a vehicle.

The fog-light circuit is not controlled by CANbus, then you can connect the DRL circuit to it. Author’s prototype is shown in Fig.

Circuit and working

The circuit diagram of the DRL controller. It is built around timer NE555, MOSFET 60NF06 , 12V, 1C/O relay, DRLs and a few other components.

There are seven wires that come out of the circuit. The first connection (DRL-B and DRL-G) you will make is to the DRLs. These are the main wires that will make the bumper DRLs turn on when you start the vehicle.

Connect DRL-B and DRL-G wires from the circuit directly to the DRLs at the bumper. The circuit activates when it senses ignition voltage. It does so by getting a signal from the main wire (IGN+) and the positive supply wire that runs from the circuit to the ignition-switched +12V power line. GND is main ground connection, and it must be connected directly to the negative battery terminal or the body of the vehicle.

The wire, if it does not reach the battery, by running sufficient length of the automotive wire from the circuit to the negative terminal of the battery. If you want the DRLs to switch off when you turn your headlights and/or parking lights on, connect HL+ and PL+ to the existing headlight and parking-light wires.

Circuit Diagram

Wire connection PB+ is optional; you do not have to connect it unless you want the DRLs to work with the parking brake . The potmeter (VR1) can be used to adjust the brightness of DRLs as per requirement. Note that, you can modify the circuit’s default Set Off mode as per your choice, or according to the relevant law of the land.

The circuit is a simple pulse-width modulator  built around the ubiquitous 555 timer. User-controllable PWM output from IC1 is used to switch on the DRLs through MOSFET 60NF06.

Note. The MOSFET from a noisy line calls for a small series gate resistor close to the MOSFET. Using a low-value 100-ohm resistor between the MOSFET driver and MOSFET gate terminal dampens down any ringing oscillations caused by lead inductance and gate capacitance, which can otherwise exceed the maximum voltage allowed on the gate terminal. Also, using pull-down 100k resistor (R5) from the gate to the source of the MOSFET is a good practice.

PCB and component 

An actual-size PCB for the DRL controller circuit is shown in Fig.and its component layout Enclose the circuit in a suitable small box with connectors CON1 and CON2 on the front side to connect the seven control signals and the DRL.

After assembling the circuit, refer to the wiring guide table before connecting these to the PCB board.
Panel-mount the input and output interface, as required.

The default Set Off mode of the DRL is given below:

IGN+ (ignition): ON→DRL: ON
HL+/PL+/PB+ : ON→DRL: OFF

switching to light emitting diode (LED) lighting for automotive headlamps because of its features such as high efficiency and long service life. In addition, from a safety perspective, applications of LED-driven daylight/daytime running lights  for vehicles are spreading in many states.

Wireless Multimedia Sensor Networks

The enormous growth of wireless communication technologies have already established the stage for large-scale deployment of wireless sensor networks. A typical WSN consists of a large number of small, low-cost sensor nodes, which are distributed in the target area for collecting data of interest. Most of the time, WSN is used for monitoring, tracking and event management related applications. WSN is not a new topic as many inventions have been done and countless applications have been successfully implemented.

The similarities and differences between ad hoc wireless networks, wireless sensor networks and wireless multimedia sensor networks . All these networks are used for small-scale and medium-scale networks that do not require a fixed architecture and can be deployed temporarily. WMSN requires a novel architecture, and the advanced protocol design and algorithms need to be implemented to fulfil the criteria. This article exposes the internal structure of the multimedia sensor node, architecture of WMSN, their challenges, research opportunities and applications.

Internal structure of the multimedia sensor node

Normally, a multimedia sensor device includes a sensing unit, processing unit (CPU), communication module, co-ordination sub-system, storage unit and an optional mobility/actuation unit. Sensing units usually have two sub-units: sensors [digital micro cameras, microphones and/or scalar sensors, and analogue to digital converters. Most of the sensors generate analogue signals which should be converted into digital form by using ADCs as these are to be fed into the CPU.

The system software in charge of coordinating sensing and communication tasks for signal processing, and it is interfaced with a storage unit. A communication Tx/Rx module interfaces the device to the network. In many applications, it has been observed that around 70 per cent of the battery is consumed for transceiver processes and the remaining 30 per cent consumption includes computational tasks, signal processing, co-ordination systems and sensor sub-units.

A coordination sub-system coordinates the operation of different network devices by performing various tasks, such as network synchronisation and location management. A mobility actuation unit can enable the movement or manipulation of objects, like motor, to track the object. The whole system is powered by a compact power unit that may be supported by an energy-scavenging unit, such as solar cells. Table II gives an overview of the features of hardware platforms for WMSNs.

WMSN architecture

The reference architecture of a WMSN, which is classified as single-tier and multi-tier architecture. Before we discuss further, it is important to know about the functionality of all components used in this architecture.

Standard audio and video sensors capture sound, still or moving images and videos of low resolution. Scalar sensors are another type of sensors that sense scalar data and physical attributes, such as temperature, humidity and pressure, and report measured values to their cluster head.

Multimedia processing hubs behave as cluster heads. These devices have comparatively large computational resources and are suitable for aggregating multimedia streams from individual sensor nodes. 

The storage hub allows data mining and feature-extraction algorithms to recognise essential characteristics of the event, even before the data is sent to the end user. The sink is a common data-gathering point of IP-less networks. It also supplies filtered data to the user at the remote end, gathered by a WMSN. Multiple sinks may be required in a large or heterogeneous network.

The gateway creates a bridge between an IP-less network and IP based network. It is an IP-addressable component of the WMSN. It gives permission to the user to monitor and control the WMSN from a remote location as it has an IP address and the capability to create a connection with the Internet.

In cluster topology, a group of nodes form a cluster, and the geographical target area is divided into numbers of clusters. Each cluster has one cluster head and one cluster member. In a cluster, two members cannot communicate directly, as shown in Fig. 3(b).

Challenges and opportunities

High data rates. WMSNs require high data rates as data is in terms of live video streaming, audio and still images. Achieving high data rates (in terms of Mbps) on available narrow channels is a challenging task. Recently, researchers started to implement ultra-wide band (UWB) technology on sensor nodes for higher data rates.

Signal detection and estimation

 Signal detection, estimation, filtering, data gathering and wireless channel separation are still open research challenges for the implementation of WMSNs. Researchers have proposed OFDMs (frequency-division multiplexing schemes) to increase data rates and remove interference between two wireless channels.

Reliability

 High information assurance is expected in WMSNs, and for that effective error detection, correction code with accuracy, robustness, resiliency and retransmission policy need to be found out.

Energy efficiency

Nodes have limited battery and, for most applications, charging and replacement of the battery is not possible. Nodes need to serve for many years. To reduce power consumption, researchers have already started designing and implementing different types of MAC protocols. Energy efficiency can be obtained by implementing new algorithms on the physical layer (modulation techniques, architecture, etc) as well as on the MAC layer.

Security and privacy

Multimedia industrial monitoring and control kind of applications require high privacy and security. Unauthenticated persons should not be able to access private data.

Quality of service (QoS) and quality of information(QoI)

High QoS and QoI are required on each and every communication layer. The resolution should be good enough at remote places. For video streaming, 5fps to 20fps (frames per second) is expected for better quality, and all layers should be designed accordingly.

Applications

WMSNs have numerous killer applications. Multimedia surveillance sensor networks can be used to enhance and complement existing surveillance systems to prevent crime and terrorist attacks. These can be used to locate missing persons, identify criminals or terrorists and record other potentially relevant activities, such as thefts, car accidents and traffic violations. With the help of WMSNs, it will be possible to monitor car traffic in big cities and on highways that offer traffic-routing advice to prevent congestion or identify violations.

WMSNs play a vital role in personal health care units. Telemedicine sensor networks can be integrated with 3G and 4G mobile networks to provide ubiquitous health care services. Patients can carry various types of medical sensors to monitor different parameters, such as blood pressure, ECG, breathing activity, pulse oximetry and body temperature. Remote medical centres or personal doctors can monitor the condition of patients to infer emergency situations. This will be more beneficial for villages and rural areas where doctors and health centres are not available all the time.

What is IoT?

IoT explained

The Internet of Things  is about giving intelligence and connectivity to almost everything. Maybe the best-known example of an IoT device is the smart thermostat, which communicates with your PC or smartphone and learns what you like and when and programmed itself.

Some devices also use sensors to detect when nobody's home to prevent waste. Where things get interesting is when you have lots of smart devices connected to each other and to a central hub, which might be your PC or a device such as your Xbox One.

With a few well-chosen devices you could automate all kinds of interesting things, so for example your fitness tracker might tell your lights when you're off to bed and then monitor your sleep to find the right time to wake you up gently, giving the coffee machine and the thermostat a nudge so the house is toasty and your coffee ready when you get up.

Your Kinect camera could monitor the house when you're at work, alerting you if it sees anything suspicious, and your fridge could add things to your shopping list when you're running low on supplies.

Windows 10 and IoT
The Windows operating system fit into all of this? 

Developers can create apps that work across all kinds of devices, and Windows 10 devices can change the way they work according to what they're connected to - so for example thanks to a technology called Continuum, a Windows smartphone can deliver a PC-like experience when you connect it to a keyboard and display.

You use the same apps, but the apps adapt - so Outlook changes from the mobile-focused version to a PC-like version. Universal apps will also work on the Xbox One, so developers can create apps that work not just for desktops and laptops but phones, tablets and consoles too.

Things get really entertaining when you add Hololens to the mix. Hololens is Microsoft's augmented reality (AR) headset, and it overlays computer graphics on the real world - so you could get it to show you an enormous TV on a bare wall, or overlay Mine-craft on your sofa.

Hololens is an early version of AR technology - in the long term we'll get AR embedded in normal glasses or sunglasses.

There are attempts to create open standards everyone can use, but there are many competing. The answer may be in what's called a bridge, a device that acts as a translator between two standards - so for example you might have a bridge that enables your Xbox One to control Home-Kit or Brillo devices, or vice versa.

Hue and cry

connected technology is Philips' Hue lighting system, which you can control from smartwatches, mobile devices and - via third-party apps - Windows 10.

The lights connect to a wireless hub that you connect to your wireless router, and you can then create light 'recipes' that change the colours and brightness. It's one of several such systems and by far the best known.

That doesn't mean its the best loved, however. While it's great fun Hue isn't cheap - a hub and three bulbs will set you back £149  and when rivals such as GE started making Hue-compatible bulbs using the same Zigbee wireless technology but with lower prices, Philips issued a firmware update that stopped third-party bulbs from working. It said it would change its mind after massive public outcry.

This demonstrates one potential danger of the Internet of Things: if you can't connect the devices you want to use, the Internet of Things is really the Internet Of Only A Few Things.

We shall have some Pi

it's a bare-bones computer kit that uses SD cards for storage and ships without keyboards, mice and other fripperies. But it's a fantastic device and it now runs Windows thanks to Windows 10 IoT Core, a version of Windows designed for the Internet of Things.

Microsoft's own demo used Windows on the Raspberry Pi 2 to control a virtual robot via a Hololens headset, overlaying computer graphics on a real, fully functional and controllable robot that can respond to voice commands.

That also means it's cheap and cheerful. For £32  you can have a kit that you can use to connect to and get data from sensors, to run robotic arms, to get information from cloud-based services on the internet and display it using LEDs or displays, to connect cameras and to do pretty much anything else you can think of. The Raspberry Pi can be as simple as a single sensor trigger events, or you can make it the brains of a complex system programmed in Visual Studio.

Moisture Monitor for Plants

Over-watering and under-watering both are harmful for plants. Roots need air as well as water. If the soil is constantly saturated, air cannot reach the roots and they suffocate. Also, excess water weakens the plant and makes it susceptible to various diseases, particularly fungal attacks. Under-watering, on the other hand, is equally harmful. Plants not receiving enough water droop from the top down and leaf edges turn brown.

Moisture monitor provides a solution to the above problem by monitoring the moisture level of the soil and producing an audio-visual alert when the moisture goes below a preset level, indicating that the plant needs to be watered.

Circuit and working

The core of the circuit is inexpensive and built around popular 14-stage ripple-carry binary counter CD4060  and a few commonly available components. Not all the outputs of the binary counter are available externally. The frequency at pin 7  of IC1 is actually divided by 24=16 compared to initial astable frequency. Similarly, Q4 will have half the frequency of Q3. Components R3, R4 and C2 set the clock oscillator frequency to control the flash rate of LED1 and the beeping rate of PZ1. Pulses are enabled when reset pin 12 is low and disabled, or inhibited, when reset pin is high.

Tthe circuit is simple and straightforward. The base of transistor T1 is connected to a gimmick potential divider comprising sensitivity control preset VR1, fixed resistor R1 and the moisture sensor probe. In standby state  IC1 is disabled because its reset pin 12 is directly tied to +9 V through resistor R2. However, when the soil is dry, transistor T1 is forward biased by VR1 and R1. This enables IC1 to oscillate. As a result, LED1 starts blinking and piezo-buzzer PZ1 sounds to indicate that the plant needs water.

PCB and component layout

The whole circuit in a suitable crystalline tube or box. The moisture sensor probe can be constructed using two small metal rods mounted vertically with a small gap about 10 mm in between them. These two metal rods must be supported by a small insulated board. You can place one flora caretaker in each plant pot for constant monitoring of soil moisture.

Vibration-Activated Smart Probe

low-cost, energy-saving and device-saving circuit for an electronics lab, service centre, electronics workshop, or wherever a CRO is in use. A vibration sensor attached to a CRO probe senses motion when you pick up the probe and turns on the CRO. It turns the CRO off when the probe is idle for a specified amount of time.

A CRO is used for a very short time. But in most cases, the user fails to switch off the CRO immediately after use. The service engineer mostly concentrates on faults rather than noticing whether the CRO is on or off. This results in wastage of power, reduction in CRO lifetime and leads to phosphorus burn in the cathode ray tube due to electrons hitting the screen on the same spot for a very long time, which again leads to reduction of CRT lifetime.

Circuit and working

The block diagram of the vibration-activated smart CRO probe is shown in Fig. A vibration sensor fixed on the CRO probe senses the vibrations picked up by the probe. This vibration signal is sensed, stored in a capacitor, compared with a reference voltage and fed to the relay driver to switch on the CRO. An additional circuitry is provided to switch off the CRO and give an audio acknowledgement in the form of a beeping sound.

The circuit diagram of the vibration-activated smart CRO probe is shown in Fig. It is built around bridge rectifier DB107 , vibration sensor HDX-2NC connected across connector CON2, quad comparator LM324 , 1N4148 and 1N4007 diodes, relay driver transistor BC547 ,12V single-changeover relay  and a few other components.

The circuit is built around IC LM324, which is a low-cost, quad operational amplifier. 

Op-amps in this circuit are configured in comparator and inverted-buffer modes.

HDX-2NC, a normally-closed vibration sensor is used. A vibration sensor is a small two-terminal component connected across connector CON2 in series with resistor R1. Point A in the circuit is connected to pin 3 of IC1, which is its non-inverting terminal. Under normal conditions, point A is connected to ground via sensor HDX-2NC. During vibration, its contact opens for a very small amount of time.

Op-amp A1 acts as an input comparator. Resistors R2 and R3 act as potential dividers and produce around 1.2V at point B in the circuit. When there is vibration, 12V is produced at the non-inverting terminal of op-amp A1, which is greater than 1.2V at its inverting terminal. As a result, around 12V is produced at the output of A1. This is indicated by the glowing of vibration-sense indicator LED1.

The 12V produced at output of A1 charges capacitor C2 via diode D1. D1 allows the flow of current in only one direction, that is, from op-amp A1 to capacitor C2. Whenever there is a vibration, C2 charges to the maximum voltage and slowly discharges through resistor R9.

Maximum discharge time of C2 is around 30 minutes. Potmeter VR1 is used to set delay. Op-amp A2 is configured as a comparator, which compares the capacitor voltage against the set potmeter voltage. When C2 discharges, voltage decreases at the non-inverting terminal of A2. When voltage at C2  decreases beyond the set voltage, output of A2 at its pin 7 goes low. Output of A2 is connected to relay driver transistor T1.

PCB and component layout PDFs

When A2 output is high, relay RL1 energises and the CRO gets AC mains power supply via relay contacts to operate it. At the same time, the CRO-on indicator LED2 glows.

On time of the CRO can be set as per requirement using VR1. With a small voltage set via VR1 at inverting terminal pin 6 of A2, greater will be the delay. Similarly, with more voltage set, smaller will be the delay.

An extra op-amp is used to provide acknowledgment to the user that the CRO has switched off after some idle time.For this, A3 is used in inverting-buffer mode. When output of A2 is high, output of A3 will be low, and vice versa.

When the CRO is off, output of A3 will be high. Due to this, the buzzer gets activated and produces a beep sound whose loudness gradually decreases within a short time. This happens because C3 initially acts as a short circuit and charges to +12V and blocks further current passing through the buzzer. Increasing C3 value makes the buzzer beep longer. This acknowledgement is like a communication between the user and the circuit. LED3 also flashes when the beeping sound is produced.

Construction and testing

An single-side PCB for the vibration-activated smart CRO probe is shown in Fig.and its component layout in Fig After assembling the circuit on the PCB, enclose it in a suitable box. Connect 230V AC input across CON1 and CON3. Connect the CRO across CON4.

Fix the vibration sensor on top of the CRO probe as shown in Fig. Use a highly-flexible and lightweight wire to connect the sensor. Connect AC mains supply’s live wire L and neutral N across CON3.

Potmeter VR1 is calibrated in terms of time.10.45V is the maximum C2 charging voltage when sensor is subjected to vibration. During calibration mark the minimum and maximum 25 minutes delays. Proposed front-panel dial is shown in Fig.

Provide proper insulation between AC and DC voltages. Ensure all test points have voltages as per the table before using the circuit. Main DC voltage at TP1 is unregulated.

Modernise Your Living With Solar

lifestyle is changing at a very fast pace, while accepting ways to save energy. However, using grid electricity is not the solution as it is too costly. Electricity generation is done using either thermal resources like coal, gas or diesel, or through other renewable sources, which involves a lot of investment. The major chunk of electricity is generated using thermal resources, which lacks both in quality and quantity due to the scarcity of initiatives to produce large amounts of natural gas and coal in India.

Corruption and theft in Coal India has forced it to miss many targets, leading to the requirement of mining new deposits. Hydro-electric power projects have slowed down in northern regions owing to ecological and environmental conditions in public interest. Thankfully, solar energy can be looked at for our growing electricity needs.

Solar energy offers multiple benefits over grid electricity, both economically and environmentally. It has increased the interest level of people in both commercial and industrial sectors. But there is a lot of confusion about the commercials of solar power. When it comes to roof-top solar installations, people are concerned about the high upfront costs involved and do not want to risk taking the first step.

                          

Drastic reduction in costs of solar PV panels

Solar energy is generated through solar photo voltaic (PV) panels that are installed on rooftops. Major cost involved in any solar system is the cost of these solar panels. In early 1977, per watt cost of these panels was US$ 76.67 as shown in Fig. 1. Over a period of time, this price dropped considerably to US$ 0.36 in 2014.

The graph in represents the fall in prices may vary as per the make of a particular solar panel. Typical price per watt of a good Indian-make solar panel can vary from ` 32 to ` 37, whereas for a solar panel from Tata Power the price can go up to ` 45 per watt. The price is further expected to fall over the next two years.

The rooftop solar systems that are being talked of here are grid-tied and grid-interactive type where solar power thus generated can be transferred to the grid.

Cost varies with size

The government’s initiative to increase installation of solar systems by allowing the sale of energy generated has created a commercial sense of solar power. This commercialization of solar energy increases as the size of the solar power system increases.

system cost per watt of sola

Cost per watt of energy from a solar system reduces considerably with reduction in cost per watt of the inverter. Panel cost reduces only marginally with an increase in system size. What does result in a drastic reduction in costs is drop in inverter costs. If you see considerable dip is seen in price per watt if the system size goes beyond 20kW, after which the price drops only marginally.

Cost per watt for each component

The investment

The initial investment is about ` 2,711,000, the benefits that you can expect include the facility of net-metering, giving you a return of about 20 per cent annually for 20 years, depending upon the per unit cost of the energy generated and the load used. To understand this better, please see the example given in the box on first page of this article.
Fig. 4 clearly shows that the money gets recovered in only four years, beyond which electricity is free. The quantum that can be saved (cumulatively) is as high as ` 2 million.

Cumulative cash flow for a 40kW system

This cash flow was calculated assuming that grid tariff will rise at a conservative five per cent per annum. Historically, it has been higher than that. Solar tariffs would either rise at two per cent per annum in PPA mode or remain the same in loan mode, in which 30 per cent cost of the system is paid upfront.

Comparison of tariffs for different models

You can comfortably say that solar makes great sense at this point and can result in high savings. It is not the cost of installation that has been holding back end customers from going solar, it is the high cost of trying something for which there is lack of demonstration available.

since standardization has not been seen in the industry yet, an aggregation might do the magic in enabling massive uptake. Sunk alp Energy has shifted to the aggregation model and Ministry of New and Renewable Energy also seems to be following this approach.

when installation of solar becomes more common, end customers will be able to install their own systems. All they would need to do is, select their components and services online and have the solar system set up in no time.

Earthquake Indicator Using Arduino , AVR ......

An earthquake is an unavoidable and unpredictable natural phenomenon that often causes damage to lives and property. We cannot fight it but we can stay alert and aware using technology that can protect us and the industry. Here a simple earthquake indicator for home and industry using an Arduino and a highly-sensitive ADXL335  accelerometer is presented that can indicate vibrations.

This project can be modified and used as a knock-and-shake detector for ATMs, vehicles or door-break alarms. But its main aim is to detect earthquakes and other seismic activities.
We know that accelerometers like ADXL335 are highly sensitive to knocks and vibrations in any of the three physical axes. ADXL335 gives analogue voltage equivalent to imposed acceleration. It has three outputs, one each for of X-, Y- and Z-axes. The three analogue outputs are wired to Arduino Uno ADC pins. Any acceleration caused due to movement in any of the axes is detected by the accelerometer and hence by Arduino ADC.

If motion is violent enough during an earthquake and crosses a certain threshold, a local alarm light (LED) glows, a buzzer sounds as well as a relay energises. While the buzzer and light is for home purpose, relay output is for industrial purpose; it can be wired to a PLC for safety interlocking of any moving machine part and furnace control for shutting these down in case of an earthquake. The threshold adjustment buttons are there for carrying out this task. An LCD has been provided for viewing threshold adjustments and for making the system user-friendly.

Circuit and working

The circuit  uses Arduino Uno board wired to ADXL335 accelerometer module with its ADC inputs, namely, X-axis to A0, Y-axis to A1 and Z-axis to A2. Two pushbuttons through supply of 5V are wired to Arduino Uno interrupt pins 2 and 3 that are pulled down to ground via resistors R2 and R1. These buttons are used for incrementing and decrementing the threshold of vibration detection. A 16×2 LCD  is wired in 4-wire mode with Arduino pins contrast control and backlight enabled.

BC548 transistor  is connected to pin 5 of Arduino for switching on the local alarm LED and a buzzer connected across CON4. Another BC548  is connected to pin 10 for de-energising a relay in case the alarm is triggered for industrial PLC interfacing for safety interlocks. Pins 11, 12, 9, 8, 7 and 6 are used for LCD control and data lines. When the setup is powered, and while it is still, it reads and stores current accelerometer values in Arduino internal EEPROM regardless of its orientation.

Since the ADC is 10-bit, special header file has been provided with the code. A five-second delay has been provided for all voltages and for the system to be stable before any initial value is read. Arduino’s microcontroller reads all three axes data from the accelerometer and stores in the EEPROM. It also stores the default threshold value of 25 in the EEPROM.

Some conventional indications on the LCD are shown here for different working modes. In initialising mode , system parameters are initialised. In monitoring mode, the system enters into monitoring mode with current threshold value displayed on the second line of the LCD.

Monitoring mode

Initialising mode

Indicating mode

In indicating mode, the system reads accelerometer values continuously and compares these with previous steady values of the accelerometer, stored in the EEPROM while initialising. If current value differs, that is, if stored value is either more than threshold value in positive side or less than threshold value in negative side, the alarm sounds and the relay is de-energised. This design and coding supports positive as well as negative values in all three axes.

Pushbuttons connected to pins 2 and 3 of Arduino serve as interrupts for incrementing and decrementing threshold values for sensitivity adjustments. For earthquakes, a threshold of 10 to 15 is good. The sensor can also be used to detect knocks and vibrations if the threshold is set to 5 to 8.

The entire setup can be wired and enclosed in a hard enclosure and mounted anywhere in industry or home. Users can also calculate resultant acceleration by using formulae of square root of X2+Y2+Z2, where X, Y and Z are outputs from ADXL335, and then compare the result with the threshold to raise an alarm. Modifications can be done by the user on the same platform.

Download source code: click here

Bio-Sense-Us with Biosensors

A biosensor is an analytical device that converts a biological response into an electrical signal. The term biosensor is often used for sensor devices used to determine the concentration of substances and other parameters of biological interest even where these do not utilise a biological system directly.

With an estimated 60 per cent annual growth rate, the major demand for biosensors is coming from health-care industry, but with some pressure from other areas such as food-quality appraisal and environmental monitoring. The current types are potentiometric and amperometric biosensors and colourimetric paper enzyme strips. However, all main transducer types are likely to be thoroughly examined, for use in biosensors, over the next few years.

A successful biosensor must possess: 

1. The biocatalyst must be highly specific for the purpose of analyses, be stable under normal storage conditions and show good stability over a large number of assays.

2. The reaction should be as independent of such physical parameters as stirring, pH an
temperature as is manageable.

3. The response should be accurate, precise, reproducible and linear over the useful
analytical range, without dilution or concentration. It should also be free from electrical
noise.

4. The complete biosensor should be cheap, small, portable and capable of being used by
semi-skilled people.

There is little purpose developing one if other factors encourage the use of traditional methods and discourage decentralisation of laboratory testing.

How does it work


The key part of a biosensor is the transducer, which makes use of a physical change accompanying the reaction, which may be:

1. The heat output (or absorbed) by the reaction

2. Changes in distribution of charges causing an electrical potential to be produced

3. Movement of electrons produced in a redox reaction

4. Light output during the reaction or a light absorbance difference between reactants and
products

5. Effects due to the mass of reactants or products

There are three so-called generations of biosensors. First-generation biosensors are those in which the normal product of the reaction diffuses to the transducer and causes an electrical response. Second-generation biosensors involve specific mediators between the reaction and the transducer in order to generate improved response. And third-generation biosensors are those in which the reaction itself causes the response and no product or mediator diffusion is directly involved.

An electrical signal from the transducer is often low and superimposed upon a relatively high and noisy baseline. The signal processing normally involves subtracting a reference baseline signal, derived from a similar transducer from the sample signal, amplifying the resultant signal difference and electronically filtering  out the unwanted signal noise.

The relatively-slow nature of the biosensor response considerably eases the problem of electrical noise filtration. The analogue signal produced at this stage may be output directly but is usually converted to a digital signal and passed to a microprocessor stage where data is processed, converted to concentration units and output to a display device or data store.

Advantages

1. Rapid, continuous measurement

2. High specificity

3. Very less usage of reagents required for calibration

4. Fast response time

5. Ability to measure non-polar molecules that cannot be estimated by other conventional

    devices

Applications

1. Monitoring glucose levels in diabetic patients

2. Food analysis

3. Environmental applications

4. Protein engineering and drug-discovery applications

5. Waste water treatment

Future prospects

Trends in biosensor technology over the past 30 years have taken this equipment from a simple and cheap component to the integration of several sensor systems into one unit including multiple components, making these systems smaller and tailored for mass production. The vision for the biosensor industry is to create micro-scale technology that will be suitable for performing sample preparation, analysis and diagnosis all with one chip.