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1. PID control of fan speed in response to error signal created by the difference between the setpoint temperature and the measured temperature at the grill level as measured by the grill temperature probe .
2. Control of the rate of temperature change by a combination of fan speed and lower vent opening – initial rate of change should be regulated at 6 degrees C per minute below set point and 2 degrees C per minute above setpoint.
3. Additional control of upper vent in the event that conditions in (2) cannot be met – upper vent opening will be reduced to choke off air flow through BBQ
4. In the event that the BBQ lid is opened resulting in a sudden temperature drop, record the event and attempt to recover temperature at the rate indicated in (2)
5. In the event that the Food temperature probes reach their setpoint, rapidly reduce the BBQ grill temperature to the Food setpoint temperature and hold.
6. In the event that 2 different food setpoint temperatures have been set and the lower setpoint temperature has been reached, rapidly reduce the BBQ grill temperature to the lower food setpoint. Send notification that 1^st food is ready.Once that food and the accompanying temperature probe have been removed, then raise the grill temperature to its original setpoint temperature and continue cooking until the second, higher food setpoint temperature has been reached.  Once again, reduce the grill temperature to the higher second food setpoint temperature and send notification that 2^nd food is ready.
7. In the event that the food setpoint temperature has not yet been reached but the grill temperature cannot be maintained (due to lack of fuel), send notification that fuel level is low and must be replenished.

A continuous log of food temperature, grill temperature, fan speed, bottom vent position and top vent position should be maintained in memory and a function should exist to download this information via a USB port to a PC Excel spreadsheet.  Memory should be sufficient to hold readings taken over a 24 hour period at 1 data point per minute for each recorded variable indicated above.  Since there are 6 variables to keep track of each minute, sufficient memory for approximately 9000 pieces of data is required.  A 2^nd function to reset the memory should also exist

A WiFi module will be included in the main controller hardware.  This module will facilitate the passing of data from the controller via connection with a standard network to a PC or any other device which can connect to that network.  Examples of data passed from the BBQ controller to the network include, all temperature setpoints (food and grill), current food and grill temperatures, BBQ cover open notification, food cooked notification, low fuel notification and, via a PC command, a complete dump of the measured temperature data stored in non-volatile memory on the BBQ controller.  After this dump occurs, the BBQ controller memory will be erased.

The WiFi module will also be able to accept commands sent from a PC or other device to the controller.  These commands include changing any of the temperature control setpoints (grill and food), changing any of the PID control constants, changing any of the times or temperatures indicated in the definitions that follow.

Definition of food cooked – when the measured temperature of the food has reached the food setpoint temperature.

Definition of low fuel – when the measured grill temperature decreases for 4 minutes while, at the same time the fan speed has increased to maximum speed and the bottom vent servo is completely open.

Definition of grill lid open – when the temperature drops by 10 degrees over a 2 minute period.

All of the time and temperature values in the previous 3 definitions must be accessible in the PC software in the event they need to be changed during testing.

Following picture shows a typical control plot of a BBQ where the grill setpoint temperature is 160C.  2 different foods are being cooked at the same time.  Each food has a different desired internal temperature represented by Food 1 setpoint and Food 2 setpoint.  Initially the grill heats up to its setpoint and as this happens, both foods start to cook.  Finally Food 1 achieves its desired internal temperature.  Immediately, the grill setpoint temperature is reduced to Food 1 setpoint temperature and a signal is sent out to the user indicating that Food 1 is ready.  Once the temperature probe for Food 1 is unplugged, the grill temperature increases to the original setpoint of 160C and Food 2 continues to cook.  When Food 2 reaches its desired internal temperature, once again the BBQ grill temp.

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