As you may have noticed this update is coming a little latter then I anticipated. Having posted a preview of the new pcb boards back in Nov. of last year. It was my hope to have a update out much sooner.
However all good things come to those who wait they say. After assembling and running the new controller through my bench testing; I decided the mcp2221a usb to serial uart chip would not be the ideal choice. Not only did I want to have the new controller compatible with GRBL 1.1 but I also wanted to have the board be compatible with estlcam.
The way estlcam works you need to reflash your atmega328 every time you make a adjustment to your settings such as those for step/mm. The mcp2221a has no hand shaking line as a example it does not have a DTR line! Not having this auto reset line would require a press of the reset switch each and every time a change to the settings was made or new firmware needed to be uploaded. Not a deal breaker but we could do better.
Now setting aside the mcp chip for this project. I began my search for its replacement. I could have gone with the atmega 8u2 / 16u2 having a few on hand. The Arduino website provides schematics and firmware for using this chip as a uart bridge. This would have made a good proven choice. In the end I decided to go with another tried and true usb uart chip from ftdi. Gasp !! I hear you now; ftdi and after the crap they pulled with ftdi gate. I know I know. Do diligence must be taken to acquire a legitimate ftdi chip. Do not buy them from ebay or aliexpress you will have nothing but problems.
I purchased my ftdi chips though a reputable dealer here in the USA Digikey and can recommend you do they same. Always name brand quality products.
So what Ftdi chip did I end up going with? Well I wanted a chip that would allow a near drop in replacement with the mcp2221a. None of the ftdi chips are through hole and I would have preferred a through hole component. Nothing can be done about that I am afraid. So the chip requiring the fewest changes to my board was the ft232rl and it has been proving itself a excellent choice.
With the new uart chip selected and Kicad schematics updated it was back to Oshpark to order my new boards. They arrived quickly as usual… This time with candy.. Nice !
Now how are we going to deal with that new little surface mount chip? In all honesty I was a bit nervous. Those are some very small pads!
However it turns out with the right set of tools it is not to bad. First thing I did was order some solder paste and a metal stencil to make the process easier on myself.
Just align the stencil and tape it down, blue painters tape works great here no residue when you go to remove the stencil which is a nice bonus.
Using a nice firm plastic card ( a store “club card” works well ) spread on a even layer of solder paste Taking care to fill in each pad. Carefully peel up and remove the stencil and see how well you did.
Nice ! always a good feeling when things go to plan. 🙂 Next it was time to place the ft232rl chip carefully on the pcb taking note of my pin one indicator.
Now there are many many ways to affix the chip to your pcb.. Drag soldering, flood soldering, pan relfow and oven reflow to name a few. When it comes to a single surface mount component on a pcb I find the quickest and easiest method is air. Yep hot air. Pick yourself up a affordable hot air gun like this unit here. This hot air gun is not only significantly cheaper then a reflow soldering station. It also comes in handy when you need to use heat shrink tubing.
Hold the Hot air gun about 2cm above your chip rotating in small circular motions. It will only take a minute or two and you can visually watch the solder flow into place pulling the chip into perfect alignment.
the rest of the board went as one would expect of a dip package board to go. I have been testing the new board running GRBL 1.1 for the last few weeks now. Bcnc , GRBL Panel, universal Gcode sender, LaserWeb3 No problems everything has been working exactly as expected.
In the coming couple of weeks I will be installing Estlcam and flashing the board and running all my tests again this time under estlcam control. If everything goes smoothly you can look forward to the new board being added to the shop towards the beginning of March. 🙂