Antenna Handbook

2-Element Yagi Array Antenna Calculator: A Complete Guide (2025 Edition)



Yagi-Uda antennas—commonly known as Yagi antennas—have long been a preferred choice for applications ranging from ham radio and amateur television to Wi-Fi and satellite communication. Among the simplest yet most effective designs is the 2-element Yagi array, consisting of a driven element and a reflector or director. This configuration is popular due to its balance between simplicity, gain, and directionality.

In this article, we will explore everything you need to know about the 2-element Yagi array antenna calculator: how it works, the physics behind it, the math involved, and how to use an online calculator to design your own high-performance antenna.

Table of Contents

  1. What is a Yagi-Uda Antenna?

  2. Components of a 2-Element Yagi Array

  3. Why Use a 2-Element Yagi?

  4. Key Parameters in Yagi Design

  5. Mathematical Formulas for a 2-Element Yagi

  6. How the 2-Element Yagi Calculator Works

  7. Step-by-Step Example Calculation

  8. Applications of 2-Element Yagi Antennas

  9. Benefits and Limitations

  10. Top Online Yagi Antenna Calculators

  11. Final Tips and Best Practices

1. What is a Yagi-Uda Antenna?

A Yagi-Uda antenna, or simply a Yagi antenna, is a directional antenna system made up of:

  • A driven element (typically a half-wave dipole)

  • One or more passive elements, which include:

    • A reflector (placed behind the driven element)

    • One or more directors (placed in front of the driven element)

Yagi antennas are widely used for their ability to focus signal energy in one direction, offering high gain and directivity.

2. Components of a 2-Element Yagi Array

The 2-element Yagi is the most basic configuration and includes:

  • Driven Element: The active radiator, typically a λ/2 dipole.

  • Reflector or Director: A passive element that alters the radiation pattern.

Two types of 2-element Yagis can exist:

  • Driven + Reflector: More common, provides modest gain with a wide beamwidth.

  • Driven + Director: Offers slightly higher gain but can be more difficult to tune.

3. Why Use a 2-Element Yagi?

While more elements can yield higher gain, a 2-element Yagi has several advantages:

  • Simple to build and tune

  • Improved forward gain (~4–5 dBi)

  • Reduced back lobe radiation

  • Compact size, ideal for portable or small-scale applications

These characteristics make the 2-element Yagi ideal for:

  • Field day amateur radio setups

  • Direction-finding (DF) antennas

  • Wireless communication experiments

4. Key Parameters in Yagi Design

When designing a 2-element Yagi antenna, you need to consider several key parameters:

Parameter Description
Frequency (MHz) Operating frequency of the antenna
Wavelength (λ) Derived from frequency (λ = c / f)
Element Lengths Physical lengths of the driven and passive elements
Spacing Distance between the driven element and the reflector or director
Impedance Matching Ensuring the antenna feeds correctly into a 50-ohm or 75-ohm system
Boom Length Total length of the boom holding the elements

5. Mathematical Formulas for a 2-Element Yagi

📏 Wavelength Calculation

λ=cf\lambda = \frac{c}{f}

  • Where:

    • λ\lambda = wavelength (in meters)

    • cc = speed of light (approximately 3 × 10⁸ m/s)

    • ff = frequency in Hz

🔧 Driven Element Length

Ldriven=λ2L_{\text{driven}} = \frac{\lambda}{2}

Or slightly less (approx. 0.47λ) due to end effects.

🔧 Reflector Length

Lreflector≈0.55λL_{\text{reflector}} \approx 0.55 \lambda

Slightly longer than the driven element.

🔧 Director Length

Ldirector≈0.45λL_{\text{director}} \approx 0.45 \lambda

Slightly shorter than the driven element.

📐 Spacing Between Elements

  • Typical spacing: 0.15λ to 0.25λ for reflector-driven

  • 0.1λ to 0.2λ for driven-director setup

6. How the 2-Element Yagi Calculator Works

A 2-Element Yagi Antenna Calculator automates the calculations based on input frequency and desired configuration. Here’s what it typically does:

  1. Accepts operating frequency (in MHz) as input.

  2. Computes wavelength (λ).

  3. Calculates element lengths based on Yagi design formulas.

  4. Provides optimal spacing between the elements.

  5. (Advanced calculators) may simulate gain, front-to-back ratio, and impedance.

Input Example:

  • Frequency: 144 MHz (2-meter band)

Output Example:

  • Wavelength (λ): 2.08 m

  • Driven Element Length: ~0.98 m

  • Reflector Length: ~1.05 m

  • Spacing: ~0.3 m

7. Step-by-Step Example: Designing a 2-Element Yagi for 144 MHz

Let’s walk through a full example.

Step 1: Determine Wavelength

λ=3×108144×106=2.08 meters\lambda = \frac{3 \times 10^8}{144 \times 10^6} = 2.08 \text{ meters}

Step 2: Driven Element Length

Ldriven=0.475×λ=0.988 metersL_{\text{driven}} = 0.475 \times \lambda = 0.988 \text{ meters}

Step 3: Reflector Length

Lreflector=0.55×λ=1.144 metersL_{\text{reflector}} = 0.55 \times \lambda = 1.144 \text{ meters}

Step 4: Element Spacing

Spacing=0.2×λ=0.416 meters\text{Spacing} = 0.2 \times \lambda = 0.416 \text{ meters}

Now you have all dimensions needed to construct a functional 2-element Yagi for the 2-meter amateur band.

8. Applications of 2-Element Yagi Antennas

Yagi antennas are used in a variety of real-world applications. A 2-element version is especially useful in:

  • Ham radio (VHF/UHF)

  • Wi-Fi (2.4 GHz directional boosting)

  • Digital TV reception

  • RFID reader antennas

  • Satellite communication (e.g., weather satellite downlink)

  • Directional jamming or detection systems

  • Emergency services and mobile command setups

9. Benefits and Limitations

✅ Benefits:

  • Simple to build, even for beginners

  • Lightweight and compact

  • Provides meaningful gain (~4–5 dBi)

  • Improves signal-to-noise ratio in one direction

❌ Limitations:

  • Less gain than multi-element Yagis

  • Narrower bandwidth than log-periodic antennas

  • Requires precise spacing and tuning for best performance

10. Top Online Yagi Antenna Calculators

If you're designing your own 2-element Yagi, here are some excellent free tools:

  1. K7MEM Yagi Calculator

  2. Yagi Calculator by VK5DJ

    • Windows application with modeling features

  3. MMANA-GAL

    • Free antenna modeling software for simulating radiation patterns

  4. Ham Radio Secrets Yagi Calculator

    • Simple HTML tool with straightforward frequency-to-length conversion

11. Final Tips and Best Practices

🧰 Building Tips:

  • Use aluminum tubing for lightweight and durable elements.

  • Mount elements on a non-conductive boom (e.g., PVC or fiberglass).

  • Ensure all connections are well-soldered or crimped to minimize loss.

🧪 Testing and Tuning:

  • Use an SWR meter or antenna analyzer to tune for lowest VSWR.

  • Adjust spacing and element lengths slightly if performance is suboptimal.

  • Test in an open area away from buildings and metal objects.

🌐 Using with a Transceiver:

  • Match impedance with a balun or gamma match to prevent mismatch losses.

  • Ensure proper grounding and lightning protection if mounting outdoors.

Conclusion: Design Smarter with a 2-Element Yagi Array Calculator

The 2-element Yagi antenna is a compact and powerful design that strikes an excellent balance between performance and simplicity. Whether you’re an amateur radio operator, a Wi-Fi hobbyist, or a field engineer, a 2-element Yagi array antenna calculator can save you time and ensure a high-performance result.

By using simple math and the right tools, anyone can build a reliable directional antenna tuned to their desired frequency. With modest effort and low cost, a 2-element Yagi can greatly enhance signal clarity, range, and overall communication quality.


read also 3 Element Yagi Calculator


2-Element Yagi Antenna Calculator

2-Element Yagi Antenna Calculator

Enter the operating frequency in MHz:

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Best Broadband Plans for Work From Home in Tokyo, Japan (2025 Guide)

With the rise of teleworking and hybrid jobs, having fast, reliable, and affordable broadband is essential—especially in a bustling city like Tokyo. Whether you're a remote worker, freelancer, digital nomad, or running a home office, this guide will help you find the best broadband plans for work from home in Tokyo, Japan in 2025.

📡 Why You Need High-Quality Broadband for Remote Work

Living in Tokyo gives you access to some of the most advanced internet infrastructure in the world, but not all plans are created equal. Here’s why choosing the right provider matters:

  • Speed: To handle video calls, large file transfers, and multiple devices.

  • Latency: Especially important for video conferencing and cloud collaboration.

  • Stability: Frequent disconnections can disrupt your workflow.

  • Support: Reliable customer service is a must when issues arise.

🏆 Top Broadband Providers in Tokyo (2025)

Here are the top broadband providers suitable for remote work in Tokyo, based on speed, reliability, coverage, and customer reviews.

1. NTT FLET’S Hikari (フレッツ光)

Overview: NTT East’s FLET’S Hikari is Japan’s most widely used fiber-optic network. Most other ISPs like So-net and OCN operate on this backbone. It offers high reliability and city-wide coverage in Tokyo.

🧾 Available Plans (via ISP partners like OCN, So-net):

  • Plan: FLET’S Hikari Next Family Type

    • Speed: Up to 1 Gbps

    • Price: ¥5,500 – ¥6,600/month (with ISP + line fee)

    • Setup Fee: Around ¥8800 – ¥22,000 (often waived in promotions)

Pros:

  • Broad coverage throughout Tokyo

  • Highly stable and fast connection

  • Can choose from many partner ISPs

Cons:

  • Complex setup (you pay for the line + ISP separately)

  • Requires Japanese language proficiency for support

2. au Hikari (KDDI)

Overview: Operated by KDDI, au Hikari is another popular fiber service, known for excellent performance in Tokyo's residential areas.

🧾 Available Plans:

  • Plan: au Hikari Home 1 Gbps

    • Speed: Up to 1 Gbps

    • Price: ~¥5,200/month (with promotions)

    • Optional ISP Bundling: @nifty, BIGLOBE, So-net

    • Discounts: Up to ¥1,100/month off for au mobile users

Pros:

  • Excellent for detached homes and family use

  • Bundling discounts with au mobile

  • High-speed and stable connection

Cons:

  • Limited coverage in certain apartment buildings

  • Requires long-term contracts for best prices

3. SoftBank Hikari

Overview: SoftBank Hikari is ideal for those using SoftBank or Y!mobile mobile phones. It runs on NTT's fiber network but includes SoftBank's own backend systems and customer support.

🧾 Plans:

  • Plan: SoftBank Hikari 1 Gbps

    • Speed: Up to 1 Gbps

    • Price: ~¥5,720/month (after discounts)

    • Mobile Set Discount: Up to ¥1,100 off/month

Pros:

  • Simple setup, good for SoftBank users

  • Good upload/download symmetry

  • Optional Wi-Fi 6 router rental

Cons:

  • Less optimal for non-SoftBank mobile users

  • Can be less reliable in crowded areas during peak hours

4. NURO Hikari (by Sony)

Overview: NURO Hikari is one of the fastest residential broadband options in Japan, offering 2 Gbps speeds. It’s ideal for power users, content creators, and tech-heavy households.

🧾 Plans:

  • Plan: NURO Hikari G2V

    • Speed: Up to 2 Gbps (download), 1 Gbps (upload)

    • Price: ~¥5,200/month

    • Contract: 2-year required for discounts

    • Setup Fee: ¥44,000 (often 100% discounted)

Pros:

  • Ultra-fast speeds

  • Flat-rate, includes ISP + line in one bill

  • Good customer satisfaction for performance

Cons:

  • Installation can take 2–4 weeks

  • Limited availability in some Tokyo apartments

5. Docomo Hikari

Overview: Powered by NTT, Docomo Hikari is a bundled internet service for Docomo mobile users. It's convenient and offers extra value through smartphone plan discounts.

🧾 Plans:

  • Plan: Docomo Hikari 1 Gbps

    • Speed: Up to 1 Gbps

    • Price: ¥5,720/month (with discounts)

    • Bundle Discount: Up to ¥1,100 off Docomo smartphone plan

Pros:

  • Convenient for Docomo users

  • Uses FLET’S Hikari backbone (stable and fast)

  • Good support channels in English

Cons:

  • Speeds and support may vary by ISP partner

  • Not a good deal unless you have a Docomo mobile

📊 Broadband Plan Comparison Chart (2025)

Provider Speed Price (approx) Contract Required Notable Features
NTT FLET’S + ISP 1 Gbps ¥5,500–¥6,600 Optional Choose from many ISPs
au Hikari 1 Gbps ~¥5,200 Yes (2-year) Mobile bundling discounts
SoftBank Hikari 1 Gbps ~¥5,720 Yes SoftBank mobile discounts
NURO Hikari 2 Gbps / 1 Gbps ~¥5,200 Yes (2-year) Very high speeds
Docomo Hikari 1 Gbps ~¥5,720 Yes Best with Docomo smartphone

🔍 How to Choose the Right Plan for Your Work-From-Home Needs

👤 Solo Remote Workers

  • Recommended: SoftBank Hikari or FLET’S with OCN/So-net

  • Why: Affordable and reliable, with good upload speeds for Zoom calls

👪 Families or Roommates

  • Recommended: au Hikari or Docomo Hikari

  • Why: Bundling discounts, stable during high use

🎥 Content Creators / Heavy Users

  • Recommended: NURO Hikari

  • Why: 2 Gbps download makes uploads, editing, and live streams seamless

🏙 Apartment Dwellers

  • Recommended: FLET’S Hikari (Mansion Type) or SoftBank Hikari

  • Why: Both are widely available in Tokyo’s apartments

🧠 FAQs: Work-From-Home Broadband in Tokyo

Q: What is the minimum speed I need for working from home?
A: At least 100 Mbps download / 30 Mbps upload. For multiple devices, aim for 300+ Mbps.

Q: Can I get an English-speaking ISP in Tokyo?
A: Some providers like SoftBank, NTT East, and Sakura Fiber offer limited English support. Consider using a service like GTN or Sakura for expats.

Q: Is installation fast in Tokyo?
A: Installation usually takes 1–3 weeks. NURO Hikari may take longer due to dual-stage installation.

Q: Are there data caps on Japanese broadband?
A: No. Most broadband plans in Japan are truly unlimited.

📍 Steps to Get Broadband Set Up in Tokyo

  1. Check Address Availability: Use the provider’s online checker with your Japanese address.

  2. Apply Online: Applications often require a Japanese phone number and sometimes a My Number card or residence card.

  3. Schedule Installation: Technicians usually visit within 2–4 weeks.

  4. Receive Equipment: Most providers ship a Wi-Fi router or ONT (Optical Network Terminal).

  5. Connect and Confirm: Ensure your upload/download speeds meet expectations.

🧾 Final Recommendation: Best Overall Plan for Remote Workers

🏆 NURO Hikari is the best all-around choice if available at your address. With 2 Gbps download speed, low pricing, and unlimited data, it's ideal for remote workers, video editors, and tech-savvy users.

For most users:

  • Best Value: au Hikari

  • Best for Expats or English Support: SoftBank Hikari

  • Most Flexible: FLET’S Hikari with So-net or OCN

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Best Broadband Plans for Home Use in Sydney – May 2025

Best Broadband Plans for Home Use in Sydney – May 2025



In Sydney, selecting the right broadband plan can be a daunting task given the plethora of options available. Whether you're working from home, streaming high-definition content, or gaming online, it's crucial to choose a plan that aligns with your usage patterns and budget. This guide explores the top broadband plans in Sydney as of May 2025, highlighting key features, pricing, and provider comparisons to help you make an informed decision.

🔍 Understanding Broadband Options in Sydney

Broadband services in Sydney are primarily delivered through the following technologies:

  • NBN (National Broadband Network): The government's initiative to provide high-speed internet across Australia. NBN plans are categorized based on speed tiers, with NBN 25, NBN 50, NBN 100, NBN 250, and NBN 1000 being the most common.

  • 5G Home Internet: A newer technology offering high-speed internet via 5G networks. Providers like TPG and Optus have introduced 5G home broadband plans in select areas.

  • Opticomm Fibre: An alternative fibre network available in certain Sydney suburbs, offering high-speed internet services.

🏆 Top Broadband Plans for Home Use in Sydney

1. Tangerine NBN 100 Plan

  • Speed: 100/20 Mbps

  • Price: AU$60.90/month for the first 6 months, then AU$85.90/month

  • Features: Unlimited data, no lock-in contract, optional home phone bundle for AU$10/month

  • Best For: Households with moderate to heavy internet usage, including streaming and online gaming.

2. Dodo NBN 100 Plan

  • Speed: 100/20 Mbps

  • Price: AU$73.90/month for the first 12 months, then AU$88.90/month

  • Features: Unlimited data, no setup fee, 30-day satisfaction guarantee

  • Best For: Budget-conscious users seeking reliable high-speed internet.

3. Swoop NBN 100 Plan

  • Speed: 100/20 Mbps

  • Price: AU$72/month (after applying code LOVE22 for AU$22 off for 6 months)

  • Features: Unlimited data, locally-based support, no congestion during peak hours

  • Best For: Users prioritizing customer support and consistent speeds during peak times.

4. Exetel NBN Superfast (NBN 250)

  • Speed: 220 Mbps typical evening speed

  • Price: AU$89/month for the first 6 months, then AU$104/month

  • Features: Unlimited data, 5 My Speed Boost Days per month, optional modem purchase for AU$170

  • Best For: Households with multiple users engaging in high-bandwidth activities like 4K streaming and online gaming.

5. TPG 5G Home Broadband Plus

  • Speed: 50 Mbps (approximate)

  • Price: AU$49.99/month for the first 6 months, then AU$59.99/month

  • Features: Unlimited data, no lock-in contract, 5G network coverage

  • Best For: Users in areas with strong 5G coverage seeking a wireless internet solution.

📊 Broadband Plan Comparison Table

Provider Plan Name Speed Price (First 6 Months) Price (Ongoing) Best For
Tangerine NBN 100 100/20 Mbps AU$60.90/month AU$85.90/month Moderate to heavy internet usage
Dodo NBN 100 100/20 Mbps AU$73.90/month AU$88.90/month Budget-conscious users
Swoop NBN 100 100/20 Mbps AU$72/month AU$72/month Consistent speeds during peak hours
Exetel NBN Superfast (250) 220 Mbps AU$89/month AU$104/month High-bandwidth households
TPG 5G Home Broadband 50 Mbps AU$49.99/month AU$59.99/month Areas with strong 5G coverage


💡 Tips for Choosing the Right Broadband Plan

  • Assess Your Usage: Determine your household's internet needs. For light browsing and social media, an NBN 25 or 50 plan may suffice. For streaming in 4K or online gaming, consider NBN 100 or higher.

  • Check Availability: Not all providers offer services in every area. Use the provider's address checker tool to confirm service availability at your location.

  • Consider Contract Terms: Some plans offer discounts for the first few months but may revert to higher prices afterward. Ensure you're comfortable with the ongoing costs.

  • Customer Support: Opt for providers with strong customer support, especially if you encounter technical issues.


📞 How to Switch Providers

Switching broadband providers in Sydney is relatively straightforward:

  1. Check Eligibility: Use the provider's address checker to confirm service availability.

  2. Compare Plans: Use comparison websites to find the best plan that suits your needs.

  3. Contact the New Provider: Once you've selected a plan, contact the new provider to initiate the switch. They will guide you through the process.

  4. Cancel Your Old Plan: After your new service is activated, cancel your old plan to avoid double billing.


🏁 Conclusion

Choosing the best broadband plan for home use in Sydney depends on your specific needs, budget, and location. The plans highlighted above offer a range of options to cater to different requirements. By assessing your usage patterns and considering the factors outlined in this guide, you can select a plan that provides reliable and high-speed internet connectivity for your household.

For more detailed comparisons and to check the latest offers, visit Finder's Broadband Comparison and WhistleOut's NBN Plans.

Note: Prices and plan details are accurate as of May 2025 and may be subject to change. Always check with the provider for the most current information.

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Capacitor Network's

 Series

CT =  1/(1/(1/C1 + 1/C2 + 1/C3))

Series
CT = (C1 * C2)/(C1 + C2)

Parallel

CT = C1 + C2 + ....CN for 2 or more capacitors

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Voltage Divider

 


Formula for Voltage Divider :

Vout = Vin * (R2/R1+R2))

Where :

R1 and R2 can be a potentiometer 

reference :

[1] Formula's, Table, and Basic Circuit, Engineer's Mini-Notebook, Radio Shack 



                                   

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VHF Test Transmitter

 


If you want to be independent of the local radio stations for testing VHF receivers, you need a frequency modulated oscillator that covers the range of 89.5 to 108 MHz — but building such an oscillator using discrete components is not that easy. Maxim now has available a series of five integrated oscillator building blocks in the MAX260x series (see the May 2001 issue of Elektor Electronics), which cover the frequency range between 45 and 650 MHz. The only other thing you need is a suitable external coil, dimensioned for the midrange frequency. The MAX2606 covers the VHF band, although the frequency can only be varied by approximately ±3 MHz around the midrange frequency set by the coil L. The inductance values shown in the table can serve as starting points for further experimenting.The SMD coils of the Stettner 5503 series are suitable for such oscillators. In Germany, they are available from Bürklin (Buerklin.com) , with values between 12 nH and 1200 nH. You can thus directly put together any desired value using two suitable coils. If you want to wind your own coils, try using 8 to 14 turns of 0.5-mm diameter silver-plated copper wire on a 5-mm mandrel. You can make fine adjustments to the inductance of the coil by slightly spreading or compressing the coil. The circuit draws power from a 9-V battery. The BC238C stabilises the voltage to approximately 4 V. Although the MAX2606 can work with a supply voltage between +2.7 V and +5.5 V, a stabilised voltage improves the frequency stability of the free-running oscillator. The supply voltage connection Vcc (pin 5) and the TUNE voltage (pin 3) must be decoupled by 1-nF capacitors located as close as possible to the IC pins. The tuning voltage TUNE on pin 3 may lie between +0.4 V and +2.4 V. A symmetric output is provided by the OUT+ and OUT– pins. In the simplest case, the output can be used in a single-ended configuration. Pull-up resistors are connected to each of the outputs for this purpose. You can use a capacitor to tap off the radio signal from either one of
these resistors. Several milliwatts of power are available. At the audio input, a signal amplitude of 10 to 20 mV is enough to generate the standard VHF frequency deviation of ±40 kHz.
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Opentherm Monitor Circuit

 


If you say that the term ‘Opentherm’ is unfamiliar to you, then this will not surprise us the least. Opentherm is a protocol, which can control central heating boilers and hot water systems digitally. ‘Open’ indicates that it is not specific to a single brand. Anyone can, in principle, make use of this protocol, provided you are prepared to hand over several thousand pounds for ‘membership’ and are prepared to keep the information secret (talk about ‘open’…). As a consequence we unfortunately do not know a great
deal about it, but we do have a few technically interesting pieces of information we would like to share with you.

The connection between the master device (usually the room thermostat) and the slave (typically the central heating boiler) consists of two wires, which permits the use of existing cabling. Via this cable the boiler powers the thermostat with DC. In order to prevent wiring errors, the thermostat is fitted with a bridge rectifier, allowing the conductors (positive and negative) to be reversed. The installer cannot make any mistakes here. The master places on this connection a digital signal. Every second, 32-bits are transmitted in Manchester-code and after about 0.2 seconds the slave responds with the return message. Every bit lasts 1 ms,
and a message consists of:

1 Start bit (logical zero)
1 Parity bit
3 Message type
4 Spare
8 Data ID
16 Data
1 Stop bit (logic zero)



From the electrical perspective, an interesting solution has been selected. The boiler sources current, a logic Low is a current between 5 and 9 mA, a logic High a current between 17 and 23 mA. This way the thermostat is always powered. In the opposite direction, the thermostat signals by pulling down the open circuit boiler voltage of 24 V to a voltage less than 9 V (logic Low) or between 15 and 18 V for a logic High. 

So, at the risk of over-emphasising: the boiler provides information by modulating the current, and the thermostat by changing the voltage. All this can easily be observed on an oscilloscope. In order to follow the activities, we have designed a circuit that does not unduly influence the operation, although it causes an unavoidably small voltage drop of course. The boiler is connected to K1; the polarity is of no consequence  because the connector is followed by a bridge rectifier (D1- D4). The thermostat is connected to K2. R4 and IC1a look if the current corresponds with a logic ‘Low’ or a ‘High’ and signal this, electrically isolated, to the DCD of the serial input of your computer. The voltage of the connection is
monitored by R6, R7 and IC1b and copied to DSR. An oscilloscope connected to these points easily shows you the messages going back and forth. It is likely that the current channel shows both messages. When the voltage on the wires changes, there is also an inevitable change in current because the thermostat is a capacitive load. The circuit is powered from the RTS and DSR hand
shaking lines. They have to be made logic Low first, of course. Naturally, it is also possible to connect a power supply of around 10 to 12 V behind the diodes. Those who are keen can write a program to read the serial inputs and decode the Manchester-code to data. Certain information, such as room and boiler temperature can easily be found. Unfortunately we do not have any more information and neither do we have a program. Every now and then there is something to be found in the Internet, so it may be sensible to keep an eye this.

source : Elektor Circuit Collections 2000-2014
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Three Component Oscillator

 


At first glance, this circuit appears to be just a primitive microphone amplifier. Why then is the title of this article
‘Three-component Oscillator’? The answer is very simple:
the microphone is not intended to pick up speech; instead, it is placed so close to the loudspeaker that massive positive feedback occurs. Here we intentionally exploit an effect that is assiduously avoided in public-address systems — the positive feedback results in a terribly loud whistle. The loudspeaker is connected directly to the 12-V supply voltage and the power transistor, so it must be able to handle a power of at least 1.5 W, and it should have an impedance of 8 to 16 Ω. An outstanding candidate can be cannibalised
from an old television set or discarded speaker box. The microphone should be a carbon-powder type from an old-fashioned telephone handset. If you place a switch in series with the power supply, this sound generator can also be used as an effective doorbell or siren. Surprisingly enough, the circuit can also be used as a simple microphone amplifier — hardly hi-fi, of course, but still usable.

source : P. Lay - Elektor Circuit Collections 
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2.5-GHz Signal Source

 


More and more communications systems are operating in the 2.4-GHz ISM (Industrial, Scientific and Medical) band, including Blue
tooth, various WLAN (Wireless Local Area Network) and Home-RF systems. A simple test oscillator for the frequency band between 2.4 GHz and 2.5 GHz can prove useful in testing receivers. Such an oscillator is available from Maxim (www.maxim-ic.com) as a single IC. The MAX2750 covers the frequency range between 2,4 GHz and 2.5 GHz using in internal LC network that can be tuned using a varactor diode that is also built into the IC. An output buffer delivers a level of –3 dBm into 50 Ω.
This component is housed in an 8-pin µMAX package. The circuit is powered from a 9-V battery. The BC238C transistor stabilises the battery voltage at around 4 V. Although the MAX2750 can work with supply voltages
between +2.7 V and +5.5 V, the frequency stability of the free-running oscillator is better with a stabilised supply voltage. All connections to the IC are decoupled using 220pF capacitors, which must be located as close as possible to the IC pins. The tuning voltage at pin 2, TUNE, may lie between +0.4 V and +2.4 V, which provides a tuning range between 2.4 GHz and 2.5 GHz. If it is desired to switch off the oscillator, this can be done by connecting the Shutdown input (SHDN) to earth potential. When the IC is shut down, its current consumption drops to around 1 µA. Here the shutdown input is connected to the Vcc potential by a pull-up resistor, so that the oscillator runs. The –3 dB output level can be reduced using the indicated pi attenuator. A number of resistance values for this attenuator are shown in the table.

source: Elektor Circuit Collections 

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Step-up Switching Regulator with Integrated Current Limit

 


In the form of the LT1618, Linear Technology (www.lineartech.com) has made available a step-up switching regulator with a current limit mechanism. This makes it easy to protect an otherwise not short-circuit-proof switching regulator: the input voltage is always connected to the output via an inductor and a diode. We can limit the current at the input (Figure 1), which limits the current drawn by the entire circuit; alternatively, with the circuit of Figure 2, the output current can be limited. This enables the design of constant current sources at voltages higher than the input voltage. In the circuit shown the nominal output voltage of the step-up switching regulator will be around 22 V. The output voltage can be calculated using the formula

Vout = 1.263 V (1+R1/R2)

The output current can be set via R3 as follows:

Imax = Vsense / R3
where Vsense = 50 mV

The IADJ input can be set to a voltage between 0 V and +1.58 V resulting in a linear reduction of the limit current.
The sense voltage of 50 mV across R3 for maximum current is reduced as follows:

Vsense = 0.04 (1.263 V – 0.8 VIADJ )

Hence, for a fixed value of R3, the VIADJ input allows the current limit to be adjusted. Note that in the first circuit the sense resistor R3 is fitted between the input electrolytic capacitor and the inductor. If R3 is fitted before the capacitor, the inductor current can not be properly controlled.
The LT1618 operates on input voltages between +1.6 V and +18 V. Its output voltage must lie between Vin and +35 V. With a switching current of 1 A through pin SW to ground, an output current of around 100 mA can be expected. The switching frequency of the IC is about 1.4 MHz, and the device is available in a 10-pin compact MSOP package.
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Li-Ion Protection Circuit

 


When a lithium-ion battery is discharged below the minimum recommended cell voltage its life expectancy is dramatically reduced. The circuit described here can avoid this by disconnecting the load from the battery when the cell voltage reaches a set level.The voltage at junction A may be set to 3 V, for example, by selecting the correct ratio of R1 and R2. When the battery voltage drops below the minimum value, the voltage at junction A will be smaller than that at junction B. The latter voltage is equal to: 

VB = 1.25 V + I R4 = 1.37 V

where:

I = (Vmin. – 1.25 V) / (R3 + R4) = 800 nA
(Vmin. = minimum value)

At this point the output of opamp LT1495 will go high, causing SW1 (a P-channel logic level MOSFET) to block and break the connection between the battery and the load. Because the battery voltage will rise when the load is disconnected, a certain amount of hysteresis is created by the addition of R5. This prevents the circuit from oscillating around the switching point. The value of R5 shown here provides 92 mV of hysteresis. So the battery voltage has to
rise to 3.092 V before the load is reconnected to the battery. An increase or decrease of the hysteresis is possible by reducing or increasing the value of R5, respectively. The required hysteresis depends in the internal impedance of the battery and the magnitude of the load current. The switching point defined by the values of R1-R2 is
quite critical with a circuit such as this. If the switching point is too high, then the available capacity of the battery is not fully utilised. Conversely, if the switching point is too low, the battery will be discharged too far with all the harmful consequences that may entail. Using the values shown here and including the tolerances of the parts, the switching point is between 2.988 V and 3.012 V. In practice it may be easier to select slightly lower values for R1 or R2 and connect a multi-turn trimpot in series with it. This makes an accurate adjustment of the switching point possible and has the additional advantage that R1 and R2 may be ordinary 1%-tolerance types.

Finally, before using the protection circuit it is advisable to first connect it to a power supply instead of a battery and carefully verify the operation of all its features!
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Mains Powered

 


Many circuits can be powered directly from the mains with the aid of a series capacitor (C1). The disadvantage of this approach is that usually only one half cycle of the mains wave form can be used to produce a DC voltage. An obvious solution is to use a bridge rectifier to perform full-wave rectification, which increases the amount of current that can be supplied and allows the filter capacitor to be smaller. The accompanying circuit in fact does this, but in a clever manner that uses fewer components. Here we take advantage of the fact that a Zener diode is also a normal diode that conducts current in the forward direction. During one half wave, the current flows via D1 through the load and back via D4, while during the other half wave it flows via D3 and D2. Bear in mind that with this circuit (and with the bridge rectifier version), the zero voltage reference of the DC voltage is not directly connected to the neutral line of the 230-V circuit. This means that it is usually not possible to use this sort of supply to drive a triac, which normally needs such a connection. However, circuits that employ relays can benefit from full-wave rectification.

The value of the supply voltage depends on the specifications of the Zener diodes that are used, which can be freely chosen.
C2 must be able to handle at least this voltage. The amount of current that can be delivered depends on the capacitance of
C1. With the given value of 220 nF, the current is approximately 15 mA. A final warning: this sort of circuit is directly connected to
mains voltage, which can be lethal. You must never come in contact with this circuit! It is essential to house this circuit safely in a suitable enclosure.

source : Elektor Circuit Collections

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Simple mV Source

 

This design can be used to simulate millivolt (mV) sensor signals for industrial control systems. Most of the new sensors used to day include some form of ‘intelligence’ at the measurement head, that is, the point at which the sensor comes into contact with what it is to measure. At this point, the sensor signal is conditioned/digitized and fed into a microcontroller that transmits a digital representation of the sensor value to the remote control system. However, there are still a number of ‘elderly’ control systems still in the field that have the intelligence remote from the sensor head. These systems rely on field wiring to convey the measured signal back to the control system.

During commissioning of these types of plant, it is useful to simulate the sensor signal to ensure amongst other things, that the sensor signal gets back to the correct terminals on the control system as they invariably pass through various junction boxes on the way. It can also be used to ensure that the control system operates correctly in response to the sensor signal. The design shown here has been used by the author to ‘bench test’ a control system prior to being installed. Please note that the design is only suitable for simple simulation and is not accurate enough for calibration purposes. Power from a ‘plugtop’ PSU (when bench testing) or a battery is fed to three current sources (diodes). Of these, I1 generates a 1.00 mA current signal, which when switched across the 100-Ω pot creates a 100-mV signal. Likewise, I2 generates a 0.25-mA signal which generates 25 mV across the pot. Current source I3 develops 3.0 mA and is used to illuminate the LED to give a power indication. The selected current source is switched via S2 to the 10-turn pot. Switch S1 is used to cleverly swap the polarity of the output signal. If the Type MTA206PA DPDT switch from Knitter is used, you get a centre-off position which actually shorts out the output signals (S1 pins 2 and 5) together, ensuring a zero output signal.

The current sources, despite being pretty expensive, are not very accurate — they have 10% tolerance! (hence the unsuitability for calibration use). If the output is too high, the tolerance can be ‘trimmed’ by fitting a bleed resistor (R1, R2) as shown in the diagram. The current sources are manufactured by Vishay/Siliconix and stocked by Farnell. The circuit draws a current of about 4.25 mA.
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Measuring Inductors


Often you find yourself in the position of needing to wind your own coil for a project, or maybe you come across an unmarked coil in the junkbox. How can you best find out its inductance? An oscilloscope is all you need. Construct a resonant circuit using the coil and a capacitor and connect it to a square wave generator (often part of the oscilloscope itself) Adjust the generator until you find the resonant frequency f. When C is known (1000 pF) the inductance L may be calculated from:

L = 1 / (4π2⋅f2⋅C)

If you are also interested how good the coil is i.e. what is its quality factor or Q, you can use the oscilloscope again. If the level of the damped oscillation drops to 0.37 (= 1/e) of the maximum after about 30 periods, then the Q factor of the coil is about 30

The Q factor should be measured at the intended operating frequency of the coil and with its intended capacitor. The coupling capacitor should by comparison be a much smaller value.

source : Elektor Circuit Collections 
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Two Position Dimmer


This super-simple dimmer consists of only two components, and it can easily be built into a mains switch. If you do this, don’t forget to first switch off the associated branch circuit in the fuse box, since the mains voltage is always dangerous! The circuit does not need much explanation. When S1 is closed, the lamp works at full strength, and the position of S2 does not matter. When S1 is open and S2 is closed, the capacitor causes a voltage drop, so the lamp is dimmed. The power dissipation of the capacitor is practically zero, so the circuit does not generate any heat. The resistor prevents sparking when S2 is closed while S1 is already closed. The value of the capacitor can be matched to the power of the lamp to be dimmed; it should be between 2 and 6 µF. Be sure to use a class X2 capacitor. Also, don’t forget that thiscircuit works only with resistive (non-inductive) loads. Unpredictable things can happen with an inductive load!

source : Elektor Circuit Collections 2000-2014


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±5-V Voltage Converter

A symmetrical ±5 V power supply is often needed for small, battery-operated operational amplifier projects and analogue circuits. An IC that can easily be used for this purpose is the National Semiconductor LM 2685. It contains a switched capacitor voltage doubler followed by a 5-V regulator. A voltage inverter integrated into the same IC, which also uses the switched-capacitor technique, runs from this output voltage. The external circuitry is limited to two pump capacitors and three electrolytic storage capacitors.

The IC can work with an input voltage between +2.85 V and +6.5 V, which makes it well suited for battery-operated equipment. The input voltage is first applied to a voltage doubler operating at 130 kHz. The external capacitor for this is  connected to pins 13 and 14. The output voltage of this doubler is filtered by capacitor C3, which is connected to pin 12. If the input voltage lies between +5.4 and +6.5 V, the voltage doubler switches off and passes the input voltage directly through to the following +5-V low-dropout regulator, which can deliver up to 50 mA. C4 is used as the output filter capacitor.

All that is necessary to generate the –5-V output voltage is to invert the +5-V voltage. This is done by a clocked power-MOS circuit that first charges capacitor C2, which is connected between pins 8 and 9, and then reverses its polarity. This chopped voltage must be filtered by C5 at the output. The unregulated –5 V output can supply up to 15 mA. The LM 2865 voltage converter IC also has a chip-enable input (CE) and two control inputs, SDP (shut down positive) and SDN (shut down negative). If CE is set Low, the entire IC is switched off (shut down), and its current consumption drops to typically 6 µA. The CE input can thus be used to switch the connected circuit on or off, without having to disconnect the battery. The SDP and SDN inputs can be used to switch the VPSW and VNSW outputs, respectively. These two pins are connected to the voltage outputs via two low-resistance CMOS switches. This allows the negative output to be separately switched off, whereby the voltage inverter is also switched off. Switching off with SDP not only opens the output switch but also stops the oscillator. There is thus no longer any input voltage for the –5 V inverter, so the –5 V output also drops out. The SDP and SDN inputs are set Low (< 0.8 V) for normal operation and High (>2.4 V) for switching off the associated voltage(s).

source : Elektor Circuit Collections 2000-2014


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