Recently on our Hack A Day forums a member asked about getting some VGA testers made in our “Request and Commissions” forum for a charity called the World Computer Exchange, who take old office PC’s and freshens them up to be used by children in developing countries for their education.
I sort of wanted to do a no brainier electronics build as I had been working on that Apple II weather display for quite a while at that point. I say no brainier because I decided to use one of the many already designed vga testers out there and all I really had to do was get it to fit in whatever box we ended up with.
I choose the deogen because it was already featured on Hack A Day, supports multiple raster patterns and resolutions (640×480 through 1280×1024), is already pretty darn small, and uses an ATTiny 2313 which is good because I am already set up for AVR micro controllers. For a case I choose to use some plastic “Ice Breakers” mint boxes, which due to their oval shape makes it quite a bit smaller than an altoids tin. The challenge is on to shove a PCB, switch, 9V battery, 2 buttons and a vga connector in the cramped space.
Join us after the break for a pile of pictures and some build notes.
First up would be the parts. I got most of the required parts from good ole Digikey. There were a few radio shack push buttons from another project, toggle switches from old dead power supplies and the VGA connectors came from a old multiport keyboard / vga switch (one of those with the giant mechanical rotary knobs). Including the parts I already had on hand the cost of a pair of these testers would run around 20$, though I got off a bit cheaper.
You can find schematics and a parts list on the main Deogen page, along with a properly laid out dual sided PCB. I wont be using the PCB as I have less space to work with, and I really do not feel like drilling holes, also the micro, power regulator, and crystal were substituted with fairly easy to handle surface mount packages. All passive components are normal through hole with their leads soldered to pads on the board. Have you seen a surface mount 18pf capacitor? At first I swore Digikey sent me an empty piece of tape!
The D shape PCB blanks were cut out on a band saw and smoothed over with a table top belt sander, and a test fit is made. As you see everything fits snugly inside of the box. At first I thought I was going to draw this PCB and reality kicked in when I remembered I needed to make a pair. Off to windows and Express PCB, where I quickly eyeballed the D shape of my PCB and laid out my design with quite a bit of slack over the rounded part.
I tried toner transfer, and I scrubbed the blanks with nylon pads, acetone, steel wool, and more acetone to get those things clean. I went to my parents house to use my dad’s brand new cannon laser printer. I used the fronts and backs of old fedex shipping label paper and how are my results?
Epic fail! I have never been good at making toner transfer boards but these are by far the worst ones ever. Toner didn’t stick and had a problem with smooshing. The iron I used is junk so it liked to scald the paper and screw up the copper surface. If that wasn’t enough, I didn’t measure the base of the switches which were too wide fit in the 2 holes I left in the PCB. After about the third time of this, I said “well its not getting any better” and I pulled out my little hobby knife and sharpie marker to fix any problems.
After etching, any left over problem areas were gouged out by using a super small chisel that came with a set of soldering picks, while under magnification. Both boards got each trace probed with a continuity meter, then all of the traces are coated in liquid flux in preparation for tinning.
Tinning is accomplished by pooling up a blob of solder on one of the large ground planes and you can simply dip into it with your soldering iron and paint over the traces. It looks a mess because the surface is not smooth caused by excess boiling flux, but one you start soldering on it, it flattens out real quick. I also scrubbed the board down with a toothbrush and denatured alcohol, this is vital or the board is coated in a thick gooey sticky flux syrup.
I soldered the components to the board in my layout. Unfortunately, in my layout, the board is mounted by the push button switches. The VGA connector has to be soldered in after both it and the PCB are mounted, so I need to start on the case.
First, the end is cut to fit the VGA connector. A template was made from a video card mounting bracket taped into place and crudely cut out, and cleaned up with a file. The PCB and battery were set in place and a mark for the power switch is made.While we are in there the (corrected) switch mounting holes in the pcb were used as guides to drill holes into the bottom of the mint box.
Back to the power switch. I measured it with my digital calipers and scribed its foot print in the bottom of the box, it was then cut out with a utility knife.
At this point I am ready to mount everything in the box, but I decided it needed some graphics too. Hopping back into windows, (because I cant get my wifi printer / scanner working right in linux) I set the box on my flat bed scanner and imported the image into inkscape to use as a template. I outlined my graphic and opened the resulting svg file into the gimp for paint, and printed it out on some feebee photo paper which is glued to the mint box.
Final construction involves first mounting the VGA connector to the box. Since its on the rounded end of the box the connector’s screw tabs were bent in to help match the contour. Next, the PCB is slid into place and I can now install the 2 push buttons through both the pcb and box. Finally the power switch is snapped into place and is re-enforced with a pretty thick bead of gorilla glue.
Final wiring is pretty simple evn though its in very cramped conditions. I soldered the 9v battery clip’s negative lead to a longer bit of wire and it iss soldered to a ground on the PCB. The positive lead goes though a diode and into the toggle switch, which is connected to the power input of the circuit. One side of both buttons is soldered to ground, and the other side each lead to a different pin of the microcontroller. Finally, the hardest part is hooking up the 6 lines coming from the VGA connector. They are; RGB that need to be soldered to the correct resistor dac, h sync and v sync which go direct to the micro controller, and a ground line (which connects all the grounds via a jumper wire on the vga connector).
Give the glue some time to dry, pop in a battery and snap the lid back on (which is now the bottom) and you are good to go! Both of the minty VGA testers work great and the Deogen setup is very handy when looking for defective LCD’s. Don’t just take my word for it, look at these happy campers!
We blasted through our huge pile of LCD’s thanks to you! they worked so well we are thinking of sending one of them off to one of our over 20 other chapters. Each month we have a group of volunteers who are regulars and some who come occasionally. everyone you see in the group photo there has dedicated a lot of their time to the cause. everyone there was impressed and appreciative of your contribution