My DIY PCB Thermotransfer Machine

[RobertGogol]

Hi
I would like to share my project with you - I'm curious what do you think about it, maybe someone will find it useful - please feel free to suggest anything or make use of it. If anyone interested, I can share shematics and code 

This project took me about 2 months and I've learned a lot.
Maybe this is the best way to learn electronics - to do something cool, and just pass thru all problems!

OK. When I discovered thermotransfer with a my wife's iron I was speachless.
It was fast, easy and cheap. But soon I doscovered that it is not predictable and I have to have lucky to make it work perfect and transfer whole PCB without "white holes" of missed toner. I was needed something reliable and repeatable, so I decided to do Thermotransfer Machine ..some kind.
In our coworking space I've founded forgotten HP laser Jet 4L - what is unique about it? Paper goes straight most way instead of be bended thru many rollers and guides.
The Fuser is at the end of chassis and paper goes perfectly straight thru it. Excellent.

I've started from mechanics. I've purged all what was unnessesary, leaved just fuser, stepper motor and a few cogs to make it able to transport PCB thru fuser. Also cut a part of printers main pcb - part with triac with belongings to control fuser's heater.
But first of all I had to understand how stepper motor works - so I've started
from zero - I was driving stepper motor with two switches to see and feel how it works!
I was playing like this (below) very long



Then I did my own stepper motor driver based on 8 salvaged mosfets - first it was driven with Arduino, later with atmega8 which controls whole machine - you'll se it later
(it was mistake - I should use new ones, because parts salvaged from old switching power supplies dont have much live before them)



after one week of struggle, inhale of magic smoke and one failure after another I've destroyed whole thing and started again - I had also to learn about N-MOS transistors, I've never used them before - at the photo you can see major big mistake of doing this driver - anyone sees?



but finnaly IT was working



comparing to what you can buy for 2$ it was big, expensive but MINE, and ...working better


done


Transport is controlled by photocells fed into atmega8 which is controlling stepper driver


to obtain final effect like this (demonstrated with business card - normaly upper white surface is transfered printout sticked to the copper side of PCB:


PWM FUSER DRIVER
after exploding a few heaters I've decided, that PWM control should be independent from MCU and driven by simple 555 PWM generator - below:


After many experiments I've figured out that PWM frequency should be 10.5Hz with 12,1% duty cycle, also suitable
number and speed of manufactured PCB passes thru fuser was established. And woila! It works perfect
Also thermotransfer of graphics for PCB front side is possible, just before that spray upper side of pcb with thermoresistant paint. What Can I say - capabilities of thermotransfer are very impressive (for me) - it just have to be predictible and repeatable. And thats exactly what my machine offers
Thank you
and ps. fuse on the left side protects 12V circuit

Below a few photos of machine and manufactured PCB - one board of a few in my modular digital / analog hybrid synth