3.8 Application Example
The TC4+ board was designed to simplify control of popcorn machine based
home coffee roasters. In such a scenario, the board would be connected as
follows.
• The INPUT (GND / VIN) screw terminal connects to a DC power supply
unit.
• The FAN (DC+ / DC-) connects to the fan motor. A suitable flyback
diode would be soldered directly to the motor terminals.
• Thermocouple channel 1 connects to a thermocouple measuring the tem-
perature of the incoming air (optional).
• Thermocouple channel 2 connects to a thermocouple measuring the tem-
perature inside the roast chamber.
• The Bluetooth header connects to a Bluetooth module.
• The OT1 screw terminal connects to a solid state relay (SSR), which in
turn controls the AC live wire going to the heating element. A thermal
fuse in series with the heater is strongly recommended.
Figure 7 gives a schematic with all these connections.
3.9 Further Connectors, Jumpers & Status LEDs
Further to the connectors discussed, the TC4+ features the headers, jumpers
and status LEDs listed below.
• IO2, IO3 break out the Arduino’s IO2 and IO3 ports and GND. Note that
IO3 is also connected to the MOSFET.
• I2C provides two 4-pin I2C headers for displays etc.
• Arduino stackable headers provide all Arduino pins. Note that IO2, IO3,
IO9 and IO10 are in use for IO2, IO3, OT1, OT2, respectively. IO4 and
IO5 may be in use for the Bluetooth module.
• BT SEL and BT RST jumpers for configuring Bluetooth connection and
optional Bluetooth reset circuit.
• Status LEDs for Power On, OT1 and OT2.
8
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