Long before the TC4+ was thought of, the home roasting community came up with an Arduino shield called the TC4, short for 4-channel thermocouple. The TC4+ is a further evolution of the TC4, incorporating a number of features to make the design more flexible and modern.
The TC4+ is strictly an extension of the TC4: The TC4+ provides all the features of the TC4, plus some extra. “TC4+ = TC4 + DC fan control + Bluetooth”, so to speak.
|4-channel thermocouple interface||Yes||Yes|
|2x SSR driver||Yes||Yes|
|AC fan control (requires extra hardware)||Yes||Yes|
|DC fan control||-||Yes|
|Bluetooth module support||-||Yes|
|Compatible with TC4 Arduino sketches||Yes||Yes|
In addition to these extras, the TC4+ has an improved board layout compared to the TC4. This allows the extra components to fit on a PCB of roughly the same size, and also improves a few of the on-board connectors for ease-of-use.
|Thermocouples||screw terminal||screw terminal|
|IO2/3||angled male headers||straight male headers|
|I2C||1x angled male headers||2x straight male headers|
|SSR drivers||angled male headers||screw terminals|
|DC in/out||-||screw terminals|
|Bluetooth header||-||angled female header|
The biggest difference is that SSR drivers on the TC4+ are by default provided in screw terminals. This makes connection to an SSR much easier.
The original TC4 provided a 4-channel thermocouple interface for temperature measurement, and two drivers for solid state relays for controlling AC heaters and fans. Over the years the TC4 has become the standard solution for DIY home roasters. I myself started out with one of these boards.
I was very happy with the TC4, except that for my own roaster I needed a few more features, like a driver for a DC fan. I originally had these on a stripboard, and then made an extra shield to be stacked on top of the TC4. Eventually though I decided to do things properly, and reimplement the whole thing on a single board. That’s the TC4+.
This would all have been purely a fun project for myself, but around the same time the TC4 became unavailable when the person making them retired. So there was a number of people looking for alternatives on the most popular home roasting forum, and on the other hand I had a few extra TC4+ PCBs lying around… And here we are.