Comment by L-P Lorentzen on July 10, 2010 at 2:18pm

hehehehe.... looks even grater then the name...

"man skal ikke drikke å bygge samtidig" ( dont drink and build /in norwegian)..

Comment by UFO-MAN on July 10, 2010 at 2:20pm

Du mener man skal ikke drikke og fly samtidig ? PS: med den autopiloten jeg har nå så kan man både drikke og bygge samtidig som man flyr. :)

73

Comment by brakar on July 10, 2010 at 3:28pm

Ja, hva pokker skal med autopiloit hvis man ikke kan fly og drikke samtidig ;-) Forsøkte selv å programmere en ardupilot som pup-til-pub gps en tid til bake, rød LED hvis en gikk i grøfta på høyre side, grønt til venstre, blå hvis man sovnet eller skulle komme til klatret opp i et tre eller en lysmast på vegen osv. (Egentlig en triggermekanisme for UAV utenfor rure, men, men). Fikk desverre aldri dratt prosjektet helt hjem, men denne tråden gir ny inspirasjon.

Som vi sier i gamlelandet,

Keep up the good work!

Comment by UFO-MAN on July 10, 2010 at 3:48pm

Pub gps kontroller ... ja den var ny! PS: har du for vane å klatre i lysmaster etter å ha drukket alkohol ?

Comment by Jeshua Lacock on July 10, 2010 at 11:12pm

Schematics? I would be interested in using something similar to control the temperature of a plastic injection nozzle for my CNC machine so I could print out plastic parts...

Comment by UFO-MAN on July 11, 2010 at 3:53am

Hi! Jeshua Lacock!

I haven't made a schematic but I will see what I can cook up.

The design idea is based on this:

I use the PWM output from the Arduino to control the duty cycle of the current in the wire (the ratio of on-time to off-time).

I don't like to worh with digital up / down button style controls as it takes too much time to step up and down with several clicks. I wanted a turning button. Therefore, an analog input was desired. I use a potentiometer to derive a variable voltage from 0-5V that is sent to the A/D input of the Arduino. The software uses this value to control the PWM counter.

The outputs from the Arduino can't sink or source nearly as much current as we need and it will not handle the voltages we need to get a reasonable dynamic range either, so we need to help it. This is done by running the current thru a FET transistor that acts as a fast on/off switch. This particular design was something I used to experiment with generating a ultrasound drive signal thru a transformer, so it is probably a little overkill. But hey, I had it laying around in my junkbox. In front of the FET it is a driver that takes care of the capacitive effect you see on FET gates (the gate needs to be "filled with electrons" and "emptied for electrons" fast to be able to switch on and off fast enough).

The software is very simple.

1) Read the A/D
2) Set the PWM
3) Go back to 1

I did work on a serial interface as well to be able to control the current from the PC thru a FTDI board.

The cabinet is something I had from another project. I just drilled a few holes in it. Nice eh... well.

Comment by UFO-MAN on July 11, 2010 at 4:03am

OK, here is the code:

//
// Usage: foam wire cutter.
// Pulse width modulation of a cutting wire with PWM output
// Heat controlled by analog input (e.g. pot)
// Control the heat precisely with turning the pot
// Can be used by a car battery, NiCD battery or other power supply
// The lPin is the pin that is connected to the FET transistor
// Author: "UFO_MAN"
// Hardware: Arduino



int lPin = 9; // FET transistor (via driver) connected to digital pin 9
int analogPin = 0; // potentiometer connected to analog pin 3 (the pot meter need a voltage on the hot side and the cold side need to be connected to ground. a 5K pot will work fine.
int val = 0; // variable to store the read value

void setup()
{
pinMode(lPin, OUTPUT); // sets the pin as output
}

void loop()
{
val = analogRead(analogPin); // read the input pin
analogWrite(lPin, val / 4);
}

Comment by UFO-MAN on July 11, 2010 at 4:16am

Here is the schematic quickly drawn up from memory:

Comment by Brendin on January 11, 2011 at 2:45pm

Hi,

 

Nice work.  Is this the most current schematic?  I thought I read that you used two fets in parallel.  Anyhow if you can share another pic of the updated schematic I will create the eagle schematic and do a board layout.  I'll create the board on my CNC router.  (I'll send you the eagle files)  I've got some atmega 48P's kicking around here I can use.  

I am starting my CNC foam cutter build and would like to use this for the hot wire.  It would be cool to include automatic temperature adjustment and on/off.

thanks!

Comment by UFO-MAN on January 11, 2011 at 2:53pm

Hi Brendin! Thanks for commenting. An Eagle Layout would be nice. However be careful when milling fiberglass substrate. Dont breathe the particles from a milling operation as they are bad for your lungs.

What I did in the last version was to actually replace the one FET with two in paralell. I just "piggybacked" one fet on top of the other (pin for pin). If you find a FET that can handle more current you probably only need one. The driver chip (EL7212) does have more than one output so you can use two outputs. Then you need to wire the pwm signal from the uC separately to two EL7212 inputs and then those outputs will need to be routed to the gates of each fet. I am not even sure you need the driver chip. An emitter follower and a resistor to ground probably would do the job. The reason EL7212 chips are used is that the gate input has some capacitance. This can reduce the swithcing speed. But in this application the switching speed is low so it is hardly a problem. I reused a circuit I used to experiment with ultrasound some time ago.

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