Please bear with me as this is my first blog and there will be a bit of a learning curve.
So I have made PCBs at home now for a few months using the toner transfer method and get decent results but there is room for improvement. The main issue I have is not getting consistent transfer from the paper to the PCB and I believe it’s because my laminator, a Scotch TL 901, doesn’t run hot enough to melt and fuse the toner well to the PCB.
I’ve decided to gut the control electronics out of the laminator and build my own PIC based control board that will allow variable temperature selection and display the current temperature of the laminator. Here is what the laminator looks like new and unmodified.
It’s a basic model that is inexpensive and works fairly well. Taking it apart just involves removing the screws from the bottom. Once it’s apart is nice to see just how simple the design is. On the left there is a small synchronous motor, on the right there is the stock control board that is surprisingly small, and touching one of the rollers there is a diode that used as a temperature sensor.
The most difficult part of this project will be creating a controller board and display that will fit into the limited space. I measured that there is 1.6 x 2.8 inches of space that should be usable for the control board. I plan on doing a custom PCB for the controller and a separate board that will contain the three 7 segment displays that will show the temperature.
Here is the schematic I came up with for the control board:
The rough parts list will be:
- PIC24F08KA101 as the brains, has enough pins and I already have a few.
- SPX1117M3-L-3-3 Low drop out 3.3V reg
- BTA06-600SW Triac to drive the heating element. I already have some and they are rated well enough.
- Digikey 567-1025-5-ND – a small PCB mount xformer. Anything very small and ~6-9V AC should be fine
- 3 x seven segment displays. Could maybe use a LCD but the LEDs will be easier to read I think.
- Diode for temp sensor, plan on reusing the current one from the laminator.
- various caps, resistors and other small components.
The PIC24F08KA101 has way more power than is needed for this application but they are not expensive at just over $2.50 each and the PIC24 from Microchip are very nice to work with. I’m using a DIP package since that’s that I have on hand but the surface mount version would have saved some space. The voltage regulator is a low cost SMD part that will save space on the board and provide plenty of power for the PIC and LEDs.
Here is what I have so far for the layout:
You can see the 20 pin PIC, 6PIN opto-isolator for driving the triac, the triac itself, the 20 pin header that will connect to the display board, the 6 pin programming header, and the large area that the transformer will occupy, as well as the two mounting holes. Overall I think it’s a pretty compact design that should bolt right in where the old control board was located. I will provide the layout for download once it has been finalized. Part 2 will be creating the display board.