Biltong Maker

This is my in progress biltong maker I am making as a present for my brother.  You ask what is biltong?   It is air dried cured beef that is eaten an a delicacy in Sothern Africa, most similar to beef jerky.

The drying cabinet work by passing warm and dry air over meat to dry it over 3-4 days. The meat is hung up in the cabinet in hooks and air is blow over the meat via the PC fan, heat (and humidity reduction) is brought into the cabinet via the car brake lights.  I control the heat and air flow via PWM to MOSFETs and BJTs.

The code offers: A  Menu screen to configure input which is spread over two pages of 2004 LCD, then operational modes have 3 auto revolving pages to give feedback. The machine can work in 4 modes being fully automatic, fully manual, fan priority mode and a heat priority. In automatic the heat source load is related to exhaust temperature and independently the fan load is controlled by exhaust humidity, priority modes is a photography concept I nicked, so fan priority runs fan load constant and auto controls temperature and vice versa for heat priority. 

In the Arduino IDE: I have used various arrays  to control the data such as;   line text, input parameters, min values, max valuess, incrementing values for user inputs and a temporary buffer.  The void loop is very short and consists of 5 while loops ,  the first while loop (1)  is the menu and is shown when Arduino boots up, when the user changes the control mode to say automatic the buffer array hold the mode status as {2}.  When the run line is selected  (line 8 of menu) the operational parameters and mode status are updated which changed the while loop to auto {2}  and then runs the machine with the input parameters.   Each of the 4 control while loop are very simple basically built up of custom function which are written further in the code, the function comprise of a read sensors, calculate new outputs, write outputs and white to display, this approach helped me as I built "modules" and plugged and played with them as needed in the different modes above. 

 For Hardware:  To give relatively smooth heat out I have used 3x mosfets shared over 5x 21w in a 2-2-1 config, so gives 40%-40%-20% of the power.  I use PWM on the mosfets to control the power out , I was concerned lamp would not work well at low duty cycles so when a "bank" of lamps is less than 50% duty cycle it is turned off and load moved onto other "banks".  The Fan is controlled by a 1N2222 with a decoupling 10uF capacitor (reduce audiable noise) and runs form 10% to 100%.   I am still to hard wire in the LED strip in and code some light effects . 

Please see video for demo.

I am not complete and still need to include automatic stop timer and include a fan RPM feedback.  Then it’s completing the woodwork and then onto debugging and tuning the code for reliability.

I hope to make this into a Gerber and produce professional PCBs for friends and family.  Possibly use the spare RX/TX headers to hook up wifi as a MRK2, way int the future.

Please see my YouTube video:

https://youtu.be/t07gM_mu18w

Main Parts Used:

Arduino Nano (Atmega328)

3x IRLZ44 mosfets

2x 1N2222 BJTs

1x 2004 LCD (with I2C converter)

2x DHT11   (looking to improve, not sure yet what)

1x 120mm PC Fan

5x 21w car brake lamps

1x 10uF electrolytic cap

Various resistors