Category: Maker

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

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

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

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.

I tested a couple of LM386 audio power amplifier modules.

The 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.