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Week 12 - Output Device

June 22018

Output Devices

Download all the files for this week from here

  • For group assignment visit here.

  • Add an output device to a micro-controller board you’ve designed and program it to do something.

Design the controller board for the final project

For this week’s assignment I decided to design the the controller board that I will use for my final project. Both the Input & Output devices are done together on the same board.

In my final project, The barrel of the extruder is to be heated at a set temperature, this will be done by 3 cartridge heaters. To measure the Temp a 100k Thermistor will be used.

BOM

  • 1 X 100K NTC Thermistor.
  • 3 X Ceramic heater cartridge 24V 40W
  • 1 X DC geared motor 14V 8Nm Torque
  • 1 X Power supply 24V 15A
  • MICRO ATMEGA328P-AU
  • Q1 16Mhz Crystal
  • C1, C2 18pF
  • C3, C4 100nF
  • R1-R8 10K
  • R8, R9 0ohm
  • Q2-Q5 IRF3710S N-FET 100V 57A
  • Q7 IOR
  • D1-D5 DIODE 1N4001
  • 7 X Screw terminal
  • 1 X MTA02-156 male connector
  • 1 X SMD male header 5X2 connector

Heating Cartridge

  • The heating cartridge I’m using are of 12V and 40W. Mosfet will be used as a switch to turn on and off the heating cartridge since Arduino cannot supply the required power.

  • Mosfet used - IRF540N. Datasheet can be find here.

  • Basic Connections : input

Electronic Design

  • I decided to make a DIY Arduino and us an ATMEGA328P-AU to control the nozzle temperature. I will use a 100K NTC Thermistor same as in a 3D printer to have accurate temperature measurements. To heat the nozzle I will use 3 Ceramic heater cartridge and for the same I will need 3 mosfet, 1 more MOSFET for the DC geared motor.

    How I designed the Board.

  • So the first thing was to decide which microcontoller to use.I decided to use an ATMEGA328P-AU instead of using the Attiny44, since I’d be needing a lot more i/o and PWM ports, also more memory.

  • The internet is full of DIY Arduino, just have to search Hackaduino and you are good to go.

  • One such reference i got for the basic schematic was from How-To: Perfboard hackduino. It’s very simple and use very little component to get going.

  • Also i looked at Satshakit for basic schematic and the selection of crystal frequency and capacitors.

  • After the basic schematic it went on to add a voltage regulator circuit since input voltage to the board is 12v which is regulated to 5v on board for atmega 328p and 12v raw for the heating cartridges. Here is a basic schematic i found on the internet. input. Source - Here

Schematic

input

Kindly open the image in new tab as to zoom and see the image clearly.

  • File’s Name in the source folder : Input/Output.sch

Board

  • Image of final board input
  • Unrouted Nets input

  • Image showing jumpers which are the unrouted nets. input

  • File’s Name in the source folder : Input/Output.sch

Traces

input

  • File’s Name in the source folder : traces.png

Milling:

  • Milling the board was pretty tricky since 328P-AU has very tiny footprint.

  • The Atmega 328 package i was using had very low clearance b/w the footprints. I edited the cad of the model and made the footprint small and have more clearance.

  • To mill the board I have used the same process described in week 5. After couple of tries I was able to mill the perfect board.

Final Board

  • Here is the milled board stuffed with all the components.

  • Front–input

  • Back– input

Here I have marked the programming and the Serial communication pins for better understanding. These pins are used to programme the board and also communicate using a FTDI cable. Bothe of the processes are mentioned in week-9 & week-13.

Programming the board

  • Programming the board is pretty simple. I used a 16mhz clock with 22pf resistor to make sure that the Arduino IDE recognises my board as Arduino UNO which it did. input
  • I used FabISP to programme the board. Here is the picture of my board marked with the IPSheader pins ; MISO MOSI VCC GND RESET SCK. Connect these to the respective ISP i[ins on the programmer and you are good to go. input input
  • After that You need to burn the bootloader. The fuses are set when the bootloader is dumped to the MCU. input
  • The final step is to programme the board, You ned to upload select upload using programmer in order to burn the code to the MCU. input
  • Done Uploading.

Arduino Output Code

Understanding PWM

  • Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a modulation technique used to encode a message into a pulsing signal. Below you can see how output signal looks like with the duty cycle. input

For better understanding of PWM Signals refer this LINK.

  • In my programme the PWM signals control the On/Off of mosfet which i turns the On/Off of the Heat Cartridge. This is done because if a constant power is supplied to the heat Cartridge it may get damaged, hence power is supplied in cycles. Also this helps in heating up the Cartridge to a desired temp and maintaining that temperature.

    • The MOSFET is controlled using an analog signal/voltage. In order to have an analog voltage, you need a DAC (Digital-to-analag converter) but since you don’t have one, you use PWM (analogWrite -terrible name for this function - ref:. By changing the pulse width, you change the average voltage supplied hence controlling the MOSFET’s current output. The PWM signal acts as a tap valve controlling the current (not ON/OFF - this would be a switch) which adjusts the flow of current, which in turn can control the temperature of the heater cartridge. ( explained by my global instrcutor : Rodney )
int ThermistorPin = A2; //Thermistor attached at analog pin A2
int Vo; 
float R1 = 10000; //voltage divider resistor value
float logR2, R2, T; 
float c1 = 1.009249522e-03, c2 = 2.378405444e-04, c3 = 2.019202697e-07; //thermistor co-efficients
#define H1 10
#define H2 9
#define H3 6

void setup() {
Serial.begin(9600);
pinMode(H1, OUTPUT); //setting pin H1 as output, goes to the first mosfet which controls the Heat Cartridge.
pinMode(H2, OUTPUT);//setting pin H2 as output, goes to the second mosfet which controls the Heat Cartridge.
pinMode(H3, OUTPUT);//setting pin H4 as output, goes to the third mosfet which controls the Heat Cartridge.
}

void loop() {
   //PWM signal values were adjusted manually by trial and error, the main aim was to have the temp being maintained at around 220 degree Celsius.         
 {analogWrite(H1, 172); //PWM signal set 172, to heat the cartridge H1
 analogWrite(H2, 172);//PWM signal set 172, to heat the cartridge H2
 analogWrite(H3, 172);//PWM signal set 172, to heat the cartridge H3
 delay(15000); //Rest period of 15 seconds for the heating cartridge
 analogWrite(H1, 20); // PWM signal set to 20, Does't let the cartridge cool Down completely
 analogWrite(H2, 20);/ PWM signal set to 20, Does't let the cartridge cool doewn completely
 analogWrite(H3, 20);/ PWM signal set to 20, Does't let the cartridge cool down completely
 }
 //Below is the temp input code
 
  Vo = analogRead(ThermistorPin);
  Serial.println(Vo);
  Serial.println(Vo);
  R2 = R1 * (1023.0 / (float)Vo - 1.0);
  logR2 = log(R2);
  T = (1.0 / (c1 + c2*logR2 + c3*logR2*logR2*logR2));
  T = T - 273.15;
  T = (T * 9.0)/ 5.0 + 32.0; 
  Serial.print("Temperature: "); 
 // Serial.print(T);
  float C= (T-32);
  float P= 0.5555;
  float temp= C*P ;
  Serial.println(temp);
  Serial.println(" C"); 

  delay(500);
  • File’s Name in the source folder - output.ino

Video

  • The heating cartridge was able to melt the filament easily.