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.

Feature comparison

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.

Feature TC4 TC4+
4-channel thermocouple interface Yes Yes
2x SSR driver Yes Yes
AC fan control (requires extra hardware) Yes Yes
DC fan control - Yes
Voltage regulator - 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.

Connection TC4 TC4+
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+.

TC4+ Evolution

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.

TC4+ board side view