Author Archive

It’s cool, so to heck with the economics!

Sunday, October 3rd, 2010

Part of the funding for AllgaierShops comes from a side hobby of mine–fixing non-working LCD monitors.  I buy them typically off eBay and sell them locally.  Occasionally, I come across a monitor that I simply can’t figure out.  Such is the case with a Dell e172FPb.  One side of the backlight inverter refuses to power a bulb, and after a second, the controller shuts down on undercurrent.  I can’t figure out why it’s not working.

So I’m upgrading it to LED backlighting.  Yeah, it’ll cost me more to do the backlighting than I originally spent on the monitor, but it’s a cool project, a technical challenge, and a good chance to practice my surface-mount soldering skills.

Here’s the board I designed and had fabricated:

It’s 3″ long and 0.3″ wide, and holds 12 LEDs (0.25″ spacing).  I didn’t know how closely I would need to space them in order to get sufficient and even light distribution, so I went on the generous side.  I had previously tried out a flexible LED strip I purchased off eBay, with LEDs spaced every 1/2″ or so, and it was quite visible where the LEDs were (and weren’t).  The LEDs are grouped in strings of three, and each board can be configured (by selective placing of components) to have either four strings of 3 LEDs or two strings of 6 LEDs, depending on the supply voltage.

Here it is, populated with LEDs:

The first string of three is tied to positive voltage, and will have a current-limiting resistor (R3) tied to ground.  The second string is tied to ground and will have a current-limiting resistor (R2) tied to positive voltage.  Alternatively, a single resistor (R4) can be placed to join the two strings and limit current for the combined 6-LED string.

Why only a 3″-long PCB?  Because I’m still working with the free version of Eagle, and so I’m quite limited on board space.  For most of my projects, this isn’t an issue, but when you need a 12″-long PCB, it’s a problem.  So I added a pair of pads on each end of each PCB, to make it easy to daisy-chain PCBs into a single, long string:

I used the straight edge of one PCB to line up each joint.  A couple big blobs of solder at each end hold the pieces together nicely.  Sure, it isn’t the strongest mechanical bond, but once they’re inside the LCD panel, that won’t be an issue.   Here’s the finished product:

And, just so you can see how far my surface-mount soldering skills have to go, here’s a closeup:

One nice thing about these boards is that you can cut one in half, in case your application calls for a dimension which is nowhere near a nice multiple of 3″.  Like this one, which requires a 13.5″ bulb.  I’ll try it with the current 12″ backlight before deciding whether to pursue it.

Woohoo! New product in!

Friday, April 16th, 2010

I sold out of my first product, a power supply for a solderless breadboard.  So I added a few features, ordered a new run of boards, and ordered a whole bunch of parts.  The PCBs came in last week, in a nice, v-scored flat pack:

That’s a 5mm LED next to it, for scale.  Here’s what the kit looks like assembled:

Want one?  It’s cheap–it’s just $4.99 over at the store.

Lots of time has passed…a little progress

Friday, April 16th, 2010

So our camera bit the dust shortly after the last post.  Since then, I have mounted the supports for the x-axis lead screws, put the gantry together, and done a few other things.  First, the assembled gantry:

And now, to slide the gantry on to the base.  I ran into a minor problem here–the gantry is about 1/8″ too narrow.  Fortunately, the 1/2″ MDF has just enough elasticity for me to force it onto the track.  It might actually be a good thing–I don’t have to worry about having enough tension to keep the gantry in place.  I will have to add some reinforcement to the vertical sides of the gantry at some point, to make sure I don’t end up breaking them.  Of course, from what I’ve heard, all it has to do is last long enough to cut the pieces for my next, better CNC machine!

Never enough clamps…

Tuesday, March 16th, 2010

Today:  put together the supports for the x-axis lead screws.  I will be using 1/4″-20 all thread (it’s cheap!).

I bought the cheapest 1/4″ ID bearings I could find.  They have a 12mm diameter shoulder and 22mm outside diameter.  That’s roughly 1/2″ and 7/8″, respectively.  Since I’m drilling the holes in MDF, there’s naturally some inaccuracy involved.  The small amount of slack will be quite welcome when the time comes to adjust the bearings’ position.

A while back, I also put together the slides for the y-axis linear bearing.  Nothing exciting here, just a couple pieces of MDF and some aluminum angle.

Big project…

Tuesday, March 2nd, 2010

I’ve been wanting to build my own CNC machine for years now, and I’m finally in a position to do so.  I’m cheap, which means I’ll be using inexpensive materials and lots of my own labor, rather than spending the money for a commercial project.

I’ve gone through a number of iterations on the design, and finally have one that I think meets the dual requirements of being A) within my skill-set, B) big enough to be useful, and C) within a modest budget.  Unlike previous iterations, I haven’t made a google sketchup model of the machine, and I’m making it up a bit as I go along, so I fully expect the design to evolve as I go.

Last weekend, I started on the base.  This is the simple stuff.  I added some bracing underneath for stiffness, and now have the two side rails for the linear bearings.

Top side of the base

It’s not much to look at, at this point.  Here’s the bottom:

Bottom side of the base