Input Devices

Download all the files for this week from here It will direct you to the week 12 folder which is the same as week 11.

• For group assignment visit here

• Measure something: add a sensor to a micro-controller board that you have designed and read it.

Designing the electronics 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 Thermistor will be used.

BOM

• 1 X 100K NTC Thermistor.
• 3 X Ceramic heater cartridge 12V 40W
• 1 X DC geared motor 12V 8Nm Torque
• 1 X Power supply 24V 30A
• MICRO ATMEGA328P-AU
• Q1 16Mhz Crystal
• C1, C2 18pF
• C3, C4 100nF
• R1-R8 10K
• 4 * IRF540 N channel Misfit
• 5 X Screw terminal

Thermistor

• For Temperature measurements a 100k NTC thermistor will be used. This is the same as used in most of the REP RAP 3D printers.

• Information, theory and basic coded for the thermistor temperature measurement is given on the reprap website.

• Basic Connections

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 baisc 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. . Source - Here

Schematic

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
• Unrouted Nets

• Image showing jumpers which are the unrouted nets.

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

Traces

• 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–

• Back– 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.
• I used FabISP to programme the board. Here is the picture of my board marked with the ISPheader pins; MISO MOSI VCC GND RESET SCK. Connect these to the respective ISP pins on the programmer and you are good to go.
• After that You need to burn the bootloader. The fuses are set when the bootloader is dumped to the MCU.
• 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.

• Done Uploading.

  Arduino Input code

• The code is taken from circuit basic’s website.

• The values of constant were perfect as i checked the value of thermistor output against a know temp source.

int ThermistorPin = A2;
int V;
float R1 = 10000;
float logR2, R2, T;
float c1 = 1.009249522e-03, c2 = 2.378405444e-04, c3 = 2.019202697e-07;

void setup() {
Serial.begin(9600);
}

void loop() {

  V = analogRead(ThermistorPin);
  R2 = R1 * (1023.0 / (float)V - 1.0);
  logR2 = log(R2);
  T = (1.0 / (c1 + c2*logR2 + c3*logR2*logR2*logR2));
  T = T - 273.15; 
  Serial.print("Temperature in celcius : "); 
  Serial.print(T);
  delay(500);
}

• File’s Name in the source folder - Temp_input.ino
  

Video

• Ambient Temperature

• Temperature Increases when in contact with soldering iron.