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

LM386 audio power amplifiers

I tested a couple of LM386 audio power amplifier modules.

LM386tThe larger one was a kit using the DIP package, the smaller came assembled and used a SO package. Both cost less than $2 each posted on eBay.


They both deliver close to 3Vpk into an 8Ω load at 1kHz when powered from 12.0V. That is close to 0.5W out, but the SO chip cannot withstand the associated dissipation of 0.5W continuous output.

Both handle broadcast program quite happily at 0.5W peak, the chip temperature rise is 15° and 25° respectively.

Simple Morse beacon keyer updated 2014/03/01


Above is a clip from W4HBK’s 40m grabber today, the signal is VK2OMD running 5W QRSS6 over a 14,700km path. We can infer (Duffy 2012b) from the 15dB S/N in that capture in 0.25Hz noise bandwidth, that in an 800Hz CW filter for say -5dB S/N (threshold of copy) we need 15dB more signal, or 160W for reliable copy. (Less power may be adequate for very short QSOs at the peak of fade cycles.)

Continue reading Simple Morse beacon keyer updated 2014/03/01

An inexpensive current limiter for flashing and initial testing of ESCs – Mk II

There is a risk of damage when flashing ESCs. It accrues from the fact that ESCs have a three-legged H bridge and if a high and low FET are turned on simultaneously, damaging currents may flow. In fact, this can be an issue if the FETs are on together for just microseconds on each PWM cycle. Loading the wrong hex module is a recipe for disaster, it may turn on FETs in an unexpected way.

So, for safety, the ESC should be powered from a current limited power supply during flashing and initial motor testing.

In a process of continuing development, this article describes a variation on the inexpensive current limiter for flashing and initial testing of ESCs – Mk I.

Continue reading An inexpensive current limiter for flashing and initial testing of ESCs – Mk II

Cooling an IC2200H


I have an IC2200H mounted on my operating table with 25mm clearance above the radio and ample room for convection currents to assist in heat removal. It is concerning that the case temperature reaches temperatures that are not safe to touch, temperatures in excess of 75° (55° above ambient) have been measured and that has not triggered the internal temperature protection… so it could get hotter still!

Whilst it might take a while for the radio to reach high temperatures, in the long term, it must dissipate around 139W when transmitting on HIGH power setting and at ambient temperatures as high as 35° in the shack. (Rated input is 15A at 13.6V for 65W out, leaving 139W of heat to be dissipated.)

This is one of those high power mobile radios that advertises no fan as an advantage, but it is clearly not up to the task!

The objective of this change is to keep the external parts below 60°, the (ASTM standard C1055  1999) 5 second human skin burn threshold.

Continue reading Cooling an IC2200H

An inexpensive medium power tuner current balun for HF using Jaycar parts

This is a project to design and build a Guanella 1:1 (current) balun suited for up to 100W on HF with wire antennas and an ATU.

For use with a tuner, the most important design criteria are:

  • high voltage withstand;
  • high common mode impedance;
  • power handling.

Continue reading An inexpensive medium power tuner current balun for HF using Jaycar parts