Electronics – Page 21 – owenduffy.net

2.4:1 balun design failure

A lost soul searching for enlightenment on impedance transformation sought advice on a transformer at 2.4 : 1 BALUN.

Inevitably one of the forum experts counselled:

Assuming your quad is a single-band HF antenna, a conventional transformer using #2 powdered iron would be my choice for the balun function. The reactance of the secondary winding would need to be at least 600 ohms.

So, let’s put the forum expert’s advice to a practical test.

Fleshing out the proposed solution

I have at hand a T200-2 core, so lets calculate the secondary turns to satisfy the proposed solution.

Above is calculation from a popular online calculator. For 14MHz, the secondary should be at least 23.8t. We will use 24t. Continue reading 2.4:1 balun design failure

Last update: 26th December, 2015, 9:01 AM

A test run of the generic heating / cooling controller with Pt100 sensor

The generic heating / cooling controller (hcctl) is a flexible bang-bang thermostat controller based on an ATTiny25.

The test load is a pot containing 1l of water and a 1200W immersion element controlled by the SSR above (on-off control). The controller board is a ‘fully optioned’ test framework, hcctl is the left hand DIP8 and the other is a TC427 H bridge (not needed for this SSR which can be driven directly from the ATTiny25 output pin) for buffered output and alarm. Continue reading A test run of the generic heating / cooling controller with Pt100 sensor

Last update: 27th May, 2015, 4:31 PM

SPI input for the generic heating / cooling controller

The generic heating / cooling controller (hcctl) is a flexible bang-bang thermostat controller based on an ATTiny25.

The project has been expanded to accept a simple SPI temperature sensor. The test case uses a MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter for K type thermocouples. The MAX31855 is around US$5 at Digikey for singles, but the tests were conducted using Adafruit MAX31855.

MAX31855

Thermocouples bring two challenges for hcctl:

low noise amplification of very low sensor voltage;
compensation of the ‘cold junction’ temperature; and
high resolution ADC.

The MAX31855 provides a solution to all of these challenges in a single inexpensive chip. Continue reading SPI input for the generic heating / cooling controller

Last update: 15th May, 2015, 5:45 PM

Adafruit MAX31855 checkout

Intending to enhance my generic heating / cooling controller to read SPI temperature sensors, I purchased an Adafruit MAX31855 module on eBay from a local supplier for about A$26 posted.

The module you might have guessed uses a MAX31855, a Cold-Junction Compensated Thermocouple-to-Digital Converter for K type thermocouple with an SPI interface. The Adafruit module includes a regulator and level translators to use it in a 5V system.

This article describes a simple checkout using a BusPirate V4. Conveniently, the MAX31855 module can be powered from the BusPirate. The thermocouple input is provided by a thermocouple calibrator.

After a short wait to allow both devices to stabilise at ambient temperature, a test was run. The BusPirate session is as follows. Continue reading Adafruit MAX31855 checkout

Last update: 15th May, 2015, 5:45 PM

Coupled coils – a challenge for hams!

One frequently sees discussions of coupled coils in ham fora, and the advice of the forum experts is commonly sadly lacking.

An example is the thread Impedance matching transformer where the OP is encouraged to make a transformer for 2:1 impedance transformation ratio based simply on turns ratio and a Rule Of Thumb for minimum number of turns.

Lets review a design where two windings of say 10µH and 20µH are wound on a toroidal core. With no flux leakage, the turns ratio would be 1:1.414. The model is a simple one of coupled coils and ignores self capacitance.

100% flux coupling

If there was no flux leakage, the mutual inductance is (10*20)^0.5=14.14µH, and we can build a three component model of the coupled coils along with the intended 100+j0Ω load.

Above the model for 100% flux coupling.

And above, the response of the network. At 7MHz, the input impedance is 48.7+j8.7Ω, not perfect, but close (VSWR=1.2). Continue reading Coupled coils – a challenge for hams!

Last update: 12th October, 2015, 8:47 AM

An inexpensive Chinese regulated power supply kit.

This article documents the build of an inexpensive regulated power supply available on the Internet for around A$15 posted.

Above is the completed power supply (with some modifications as discussed below). Continue reading An inexpensive Chinese regulated power supply kit.

Last update: 4th May, 2015, 6:39 PM

Using a Pt100 RTD with my generic heating / cooling controller

Generic heating / cooling controller describes a bang-bang type thermostat based on a AtTiny25.

This article works up an example application using a Pt100 RTD sensor. Pt100 is the designation for a platinum (Pt) resistance temperature detector with nominal resistance of 100Ω at 0°. Pt has a nearly linear resistance / temperature characteristic and high accuracy. Continue reading Using a Pt100 RTD with my generic heating / cooling controller

Last update: 15th May, 2015, 5:45 PM

N2006P PID checkout #1

The N2006P is a inexpensive PID controller, typically for heating and cooling operations. There are lots of similar devices for under A$20 on eBay.

Above, the controller in a minimal test harness using a Type K Thermocouple for temperature sensing and 40A SSR mounted on a heatsink. (The SSR output should be protected with an MOV for inductive loads.) 480VAC 40A SSRs sell for as little as A$5 on eBay. Continue reading N2006P PID checkout #1

Last update: 5th May, 2015, 1:01 PM

A new impedance calculator for RF inductors on ferrite cores

Some time ago I published a calculator for estimating the impedance of RF inductors on toroidal ferrite cores (Calculate ferrite cored inductor).

The calculator (input form above) use the core dimensions and complex permeability as the basis for calculation.

There are some popular cores that are not simple toroids and so not suitable for direct use with that calculator. For these cores, a practical method is to measure the inductance constant Al (inductance of 1 turn in nH) at low frequency (where µ=µi), and using the µ’,µ” characteristic from the datasheets, to calculate the impedance at the desired frequency. Note that µ’,µ” are usually frequency dependent for ferrite materials. Continue reading A new impedance calculator for RF inductors on ferrite cores

Last update: 26th March, 2015, 10:38 AM

Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites #2

This is a follow up to Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites.

Steve saw the above article and revisited the FT240-52 measurements which he apparently did, and found them wanting: Continue reading Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites #2

Last update: 28th February, 2015, 6:42 PM