DIY Digital Readout Project Update - Display Boards Are Here
Wednesday, February 15, 2012 |
| Ten brand-spanking-new LED display PCBs for the DRO project |
A week or so ago I finished laying out the LED display PCB for my DRO project. I built one unit some weeks ago using a prototyping board, but when a friend asked me to built one for her husband, I decided to bite the bullet and make a proper circuit board. This is by no means necessary, but wiring three MAX7221 on a prototyping board isn't my favorite pass time. Additionally, by using surface mount parts I was able to squeeze 24 digits (three rows of eight digits) and six tactile switches into a 5.75” x 3” board, whereas the initial prototype took 7”x5” prototype board for 18 digits (6x3) and no buttons.
Tramming Harbor Freight/Grizzly Mini Mill Column and Head
Saturday, February 4, 2012Yesterday I installed the "Large Table Assembly" and the "Air Spring Kit" from LittleMachineShop.com, so today was the time to tram the column and the head. I've seen some people tramming the column by attaching a dial indicator to the quill and adjusting the column unti the reading on both end of the table are equal. There is one huge flaw with this method: it doesn't tram the column, it trams the spindle. If you look carefully, the head is composed of two castings. The part that holds the bearings and the spindle is held by grou long bolts, and, you guessed it, is not always parallel to the dovetails. A tell-tale sign that your mill has this problem is when you jobber drill bits miss the spot that you started with the started drill bit. Essentially the head is perpendicular to the table but the column being at the angle offsets the head in the X axis as you move it up and down.
Alignment Problems with Large Table Assembly
X2 Mini Mill Table and Air Spring Installation Progress
Large Table Assembly for X2 Mini Mill
Tuesday, January 31, 2012 |
| Mini Mill Large Working Table Next to The Stock Model |
I've had my Harbor Freight mini mill for over a year. Overall I like the mill, and can't imagine living without it, but after I started making some larger parts for my CNC router, I keep bumping into the limited Y and Z travel. I was almost set on getting an X3 mill, but one evening, while browsing LittleMachineShop's catalog I noticed that they had a "Mini Mill Large Table Assembly" for $299.95 (roughly $340 shipped). According to the description, the table provides 30% of extra movement on both axes. Long story short, I placed my order last Thursday and today UPS dropped (literally) the package at my garage door. The table came preassembled in a standard wooden shipping box, bolted down to the bottom board with two bots. UPS managed to seriously bust the box, but luckily the contents were undamaged. I haven't had a chance to install it yet, since I'm doing some other upgrades at the same time.
LED Display for DIY DRO - Introduction to MAX7219/7221
Friday, January 27, 2012This is the first part of a tutorial on driving MAX7221/7219 display drivers with STM32VLDiscovery board. In this part we will cover the basics, i.e. how 7-segment display work, how the shift registers work and how to talk to MAX7221/7219 chip. In the next section I will post the source code for STM32 Value Line Discover board and explain the kay points.
As I mention in the post on DRO Design Considerations, I decided to use standard 7-segment LED display for the position readout. Since the DRO is targeted at a small milling machines, 6 digits per axis is more than enough *. This means that we need to drive 18 dits total, and by far the most convenient way is provided by Maxim 7221/7219 shift registers. Many hobbyist are intimidated by these ICs, but under the hood they are very simple. Both chips use SPI protocol to receive data and can drive up to 64 LEDs, or 8 7-segment displays. MAX7219 and MAX7221 are almost identical, with one minute difference: MAX7219 is not SPI-compliant. I will elaborate on this a bit later, but for this project they are interchangeable.
