Recently on the Workshop88 mailing list, there was a discussion of things that could be shown at the STEAM fair (STEAM stands for Science, Technology, Engineering, Art and Math) at Glen Ellyn Public Library March 8. Jim Williams said an oscilloscope is a good thing to generate interest. I added the link to the oscilloscope vector Christmas tree that made the rounds two years ago. That was such an intriguing hack that I built it immediately. It requires only four parts besides the Arduino and the scope. Arduino does not have Digital-Analog Conversion hardware but the mega328 chip can do Pulse Width Modulation and johngineer uses that capability, integrating the pulse train in an RC network for his Christmas tree. Here’s the tree on my ancient Kikusui 5630:
Many people commented in johngineers blog and offered other vector images.
The possibility of an analog scope demo at the library set me to searching the internet for other interesting vector applications. I found this Youtube video encouraging, and there are a number of vector clocks out there. Then I found a page from hudson at the NYC Resistor makerspace site discussing vector generation on the AVR chips. That post mentioned the Hershey simplex fonts, with a link to a discussion and code. That implementation appears to be very old as the ^ (circumflex) symbol renders as an up arrow and that change was made to the ASCII character set in the sixties. It’s a proportional font and there is a column for the character width.
I decided to try implementing the Hershey font using johngineers simple RC integrating network. After some manipulation and scaling the font table I was able to display single characters entered from the serial port of the Arduino:
This is the absolute worst case glyph, uses all 56 vector pairs. One problem with vector fonts is the more vertices, the longer it takes to render the character. A problem that is exacerbated by the RC integrating network.
Some of the Hershey characters have skips indicated by a -1,-1 XY value pair. For example, the equal sign is rendered as two disconnected lines. A skip indicates that the vector trace needs to be turned off while moving to the next point. Fortunately my old oscilloscope has a Z axis input and by using a third Arduino digital pin, I was able to easily implement blanking.
Here’s a picture of the Arduino showing the two integrating networks. The black wire goes to ground. My scope’s Z axis is connected through a third 10k resistor.
I found the Arduino quickly runs out of memory when you’re dealing with a 95 x 112 array so I had to learn how to force data into the flash program space using the PROGMEM keyword. I found an example that did almost exactly what I needed to do.
I’m old enough to remember Don Lancaster’s TV Typewriter. I thought it would be an even more interesting display if I could get multiple characters on the scope. So much programming and debugging later I have that working. I only made a 2×5 display as it’s just too slow. Filling all ten vector characters with the worst case @ sign takes close to a second to write the screen, but normal text is easily readable. Here is a group of letters:
and here is the number display:
Displaying multiple characters also requires blanking the trace between glyphs.
The Serial debug console that comes with the Arduino IDE can be used to enter text but a character-at-a-time terminal program works better. I use Minicom.
Note the rounded parts are much brighter than straight lines. This again is because there are more closely spaced segments and therefore the curves are painted more slowly. Also note some characters are distorted, like the seven above. I think this is because he RC integrating network continues to integrate the previous move while the next move is being generated. The first character position in each line is particularly subject to this distortion because the beam has to move a large distance from the last character.
The NYC Resistor page implementation does not use Arduino PWM, he uses an R-2R ladder DAC. This would be a great improvement from my simple RC network as all the delays in the sketch needed to wait for the RC network could be removed.
Richard Chapman KC4IFB had an article in the Sep/Oct 2009 QEX magazine for constructing an Iambic Keyer on the Arduino platform. I downloaded the code from the QEX web site, and found it worked well. I have not been active in Ham Radio for many years and my morse code is seriously rusty, so I decided to build a keyer for practice purposes and maybe to use on a real radio some day when I figure out how to get an antenna up on this small lot. I have a WB4VVF Accu-Keyer I used with my homemade paddles long ago. I bought the PC board from WB4VVF himself at the Dayton Hamvention in 1976. Chapman’s keyer implementation on the Arduino felt exactly the same and I had no problem getting used to it.
The first order of business was to see if Chapman’s code would run on an ATtiny85 chip. These are beautiful little microcontrollers in an 8 pin DIP package. They have 8K of internal flash memory and with a minor bit of library downloading, are programmable via the Arduino IDE. There is a catch though, tiny85 does not normally have bootloader code like a formal Arduino does so you need additional circuitry to burn your sketch onto the little chip. In July 2013 Jim Williams from Workshop 88 in Glen Ellyn conducted a class in tiny85 programming which I attended. At the end of the class we all had our own Arduino ISP adapter board and could burn a tiny85 by using an Arduino UNO as an intermediary.
I amped up my ISP a bit by adding a ZIF socket. It also can program the MEGA328 chips by moving five jumpers.
With the ISP programmer working, I was ready to work on the tiny85 port. I found Chapman’s code worked but there was no side tone generated. After a few hours debugging I noticed Chapman’s code was turning the tone on in every iteration of loop(). The tiny85 did not like that. I just added a flag so tone was turned on once, then left on, and the tiny85 port was working 100%.
I wanted SMALL so I added code to eliminate the speed potentiometer. In my version, you hold both paddles closed for 5 seconds and it goes into speed set mode. Dots increase the speed and dashes decrease. Another five second Iambic squeeze and it goes back to normal mode. Also I added a Straight Key mode. If a two conductor instead of a three conductor plug is inserted in the paddle jack it will just beep out what it sees on the dot paddle. Good for code practice with my J38 if I can remember where I put it.
This is the finished Keyer in the mandatory Altoids enclosure (but note SMALL Altoids):
It was a challenge to get everything in there and still have the lid close. The speaker is from a defunct greeting card but rest of the parts were purchased from Jameco. In the end, the most expensive single component was the Altoids mints from the drug store. The ATtiny85 chips are less than a dollar if you buy ten.
There are these few parts required:
There is a short video of the keyer in action here. So now if I spend a few minutes every day practicing I might get back to the 13 WPM I had to do to get my current license.
I am a big fan of Roy Underhill’s “The Woodwright’s Shop”. Last fall was the 32nd season, and he’s still wearing the same hat. The second episode was titled “The Eleven Grooved Box”, a project Roy uses in his woodworking school. You can see it here. I was attracted to this project because he uses Stanley 45 combination planes to make all eleven grooves. I have a Stanley 45 and have been looking for an appropriate project so I am trying to duplicate what Roy does as closely as I can.
You should watch the half hour video to see how Roy makes the box. I am going to document how I do it, and pass along some things I learned, and in particular, show how I made those #$%@! spline grooves. Each corner of the box has to have two matching grooves plowed for splines, without these the box would be very weak. You can see these in the corners of the lid in the photo. Cutting those spline grooves with an old Stanley 45 might be easy for Roy but for everyone else it’s a pain. A millisecond of inattention and the sides of the groove are ripped up. So like any self respecting woodworker, I made a jig.
My grooving jig for the Eleven Grooved Box
After almost giving up on this project, I sat down and analyzed what is happening. When plowing the grooves, you have to hold the plane perfectly perpendicular to the 45 degree mitered surface. The fence on the Stanley plane rides on the reference surface. But the skate is captured in the plowed groove! If you let the plane roll to the right, the fence lifts off the reference surface a bit and not much happens. But if you let the plane roll to the LEFT, the fence digs into the reference surface and pulls the blade to the left. The result is a horribly shredded edge on the left side of the groove. In the video, Roy has an Iron Arm and holds that Stanley perfectly aligned through the whole operation. My arm is made of rubber so I knew I had to make a jig to get the plane to behave.
V1.0 – My first jig attempt was a piece of 2×6 cut off at one end at 45 degrees, with a stop block attached. The stop block helps control tear out at the end of the cut and makes it easier to initially align the work piece with the plane. It did not help with the left side shredding problem, in fact made it worse.
V2.0 – Added a second 45 degree cut at the end of the 2×6, creating a 90 degree angle at the tip. That spaced the work piece farther away from the fence face. I reasoned that the longer roll radius would pull the blade over less if I let the plane drift off axis. It helped a little but still not satisfactory.
V3.0 The third revision adds a second reference surface for the BOTTOM of the plane fence.
The fence is now constrained by hard surfaces in the down and right directions, and in the up and left directions by my left hand. It can only move back and forth like it’s supposed to. The whole thing gets clamped in a bench vise for the plowing operation, just like in the video.
The bottom reference surface is constructed at the rear of the jig by screwing on a 3/4 piece of scrap cut off at 45 degrees at the top. That 45 degree surface is 90 degrees from the fence reference surface of the jig. The two screws are in elongated slots so the added piece can be adjusted up or down, which in turn moves the small block of hard wood up and down the fence reference surface. I made a one time tweak so the plane is level and aligned with the work piece bevel at the beginning of the cut and tightened the screws.
There is a small block of hard wood on which the plane fence actually rides, that sits loosely on top of the added piece.
The hardwood block has screws inserted in each end so it won’t slide off the jig when the plane is working.
I start the cut with one light pass at the end so I can see where the plane is plowing, then knife down the grain like Roy does. With that, and the v3.0 jig I’m getting perfect spline grooves in the mitered surface.
Stanley 45 tips for the Eleven Grooved Box
1. The eighth inch wide inch cutter needs to be as sharp as possible. I use one of the cheap “Eclipse Style” honing guides. I had to file the rounded jaw slightly to get it to grip the small cutter firmly. Use a simple wooden stop gauge to set the cutter for a 35 degree sharpen angle. Then the problem is, the narrow cutter can’t keep the gauge from wobbling during the honing process. The local hardware store had nylon bushings exactly the same diameter as the guide roller, with an ID the same as the guide screw shaft. I pulled the knob off the screw shaft and hacksawed a screwdriver slot across the end. With the knob removed, I can put a nylon bushing on each side of the guide and they act as outriggers to keep the whole thing true to the stone.
To be really sharp, you have to flatten and polish the back side of the cutter as well. This is complicated by Stanley having made the 45 cutters slightly curved. You can use the Charlesworth ruler trick but you will need a thicker than usual ruler because of the curve. I found it good enough to just free hand polish the back by putting a lot of finger pressure on the tip.
2. Use a good ruler and measure the distance between the fence and the skate at front and back. Mine is typically wider at the rear, which causes the skate to bind in the groove. Loosen the fence rear lock screw and push it around until the measurements are the same.
3. Wax (Paraffin from a candle) the face of the fence, the bottom of the fence, the bottom and side of the skate.
4. Don’t overtighten the cutter lock bolt. It doesn’t take much to hold the eighth inch cutter in place.
5. Use an eighth inch drill bit to set the depth stop. When the groove is finished, lay the drill bit in the trench and if it sticks up above the beveled surface, back off the depth stop and cut a little more.
Glue up tips for the Eleven Grooved Box
1. Glueups have to be rehearsed. Make sure you can get the box assembled before the glue starts to grab.
2. I’m using Titebond III which has a little bit longer open time than Titebond II. I don’t have a Roy Underhill style glue pot.
3. Use an acid brush with the bristles cut off to about 3/8 inch to apply glue. Avoid applying a lot to the inside edge as squeeze out is difficult to remove there.
5. Apply glue to all the miters and grooves then wait a minute for that to soak into the end grain. Then apply another coat of glue and insert the splines. An easy way to apply glue to the splines is to lay a sheet of foil or waxed paper on the bench, make a puddle of glue, and roll the spline around in that.
5. Don’t forget to insert the top and bottom panels. DAMHIKT.
See the original “Woodwright’s Shop” video here.
I’ve made about a dozen of these now and will document the next batch here with photos. Most of the boxes I’ve made lately are in Cherry or Walnut and are pencil box size, 3″ x 8″. These next few will be larger, sized to hold 3″ x 5″ index cards.
The lumber for this project is leftover tongue and groove wainscoat paneling from my fathers house circa 1974. These were milled 5″ wide and 11/16″ thick. He never finished the basement so after 35 years, some of the stock was available. The Cherry had darked quite a bit and that had to be planed off to get an even color on both sides of the boards.
I cut 24 inch sections and resawed to produce a 3/8″ slab for the box sides, and a 3/16″ part for the top and bottom. Should be a great grain match. The first board was resawn by hand with a good old Disston rip saw but I did not like the results. It’s too hard to get a clean line and is a LOT of work. The other boards I resawed on a table saw. All were cleaned up and thicknessed with a Dewalt lunch box planer. That will be the last power tool used on this project, all hand tools after that. I suspect the lumber Roy uses in his classroom and the video comes from Lowe’s (it is 3 1/2″ wide) so I don’t feel bad about preparing the stock with power tools. Planer scallops and snipe were removed from all faces with a #4 smoothing plane.
The thin strips in the center of this photo were ripped from another piece of cherry. They will form the box lips.
The boards still have parts of the tongue and groove machining which had to be removed. Here I’m using a 100 year old Stanley 606 to shave off the unwanted projection.
My planing discipline is not that great. I admire people like Roy and Bill Anderson who can unerringly carve off a perfect 90 degree edge free hand. I have to cheat. I have this little Stanley 95 edge plane that is made for truing up board edges. A couple of passes is all it takes.
The workbench in my shop is a recycled office desk, is not very flat, and no end vise, so some time ago I made a flat plywood planing board. It has a cam arrangement to clamp the workpiece. For these thin pieces I have to raise the work up to clear the stops. I use old printed circuit board material under the workpiece. With the 3/8″ material clamped and aligned with the planing board edge, I can cut the first 1/8″ groove. This will hold the bottom of the box and is cut against the grain of the lumber. The Stanley 45 does not seem to mind grain direction much.
Groove number two is also 1/8″ and is made by flipping the workpiece 180 degrees, and plowing the other edge. This will hold the top of the box and is cut with the grain. I have switched to the short rods in this photo.
Groove number three is a wide 5/8″ and will ultimately hold the lip. I can cut this with the same board set up as groove #2 which is why groove 2 is set up with the grain. Groove 3 is spaced down far enough so 3×5 cards will stick out a bit from the box bottom.
All these grooves are started far end first and gradually worked back to the near end. This technique gives the front of the skates a channel to follow as the groove lengthens and deepens. To minimize skate dragging against the side of the groove, It’s important to check during set up, that the skates are parallel with each other and parallel to the fence. Waxing the skates with paraffin once or twice during the operation helps a lot.
For the lip groove, I’m using both depth stops as Roy does in the video, each set to 1/8″ depth. Here I’m checking groove depth with a 1/8″ brass block. A set of these gauge blocks is very handy.
See the original “Woodwright’s Shop” video here.
In the center of the first photo in Part 1, you see narrow strips of Cherry. These must be precisely fitted into groove #3 before the board can be sliced into four box sides. The strip forms the lip around the inside of the box bottom that the lid seats onto. Roy glosses over this step in his video, he uses a strip already planed to width.
I was using a “Moxon” style vise wide enough to clamp a 24 inch strip for planing but found it didn’t hold securely enough to work the edges. Also it was a pain to insert and remove the strips. The strips are flexible enough in the wide dimension to bend and cause trouble while you’re planing. That’s probably why Roy skips over this step. I now have a better method using the dog holes on my nice flat planing board.
I insert pegs in the holes at about a 6 inch interval then weave the thin strip around them. This has several advantages:
The photo shows one of the strips and the board it will be fitted into. I’m using the #6 Stanley which has a bed long enough to nicely ride the curved strip.
It takes many tries to get the strip to fit tightly. Sometimes part of the strip fits but in other places it’s too wide, then a block plane is best to shave a small area. It’s not fatal to have the strip a bit loose in a few spots. It just has to stay in place during the next planing operation, and while slicing the board into four mitered side pieces.
At this point, the strips project above the side stock about 1/16″, I tap them in with a rubber mallet to make sure they’re seated in the groove.
Next, the fitted strips get planed down level with the grooved board. I use a thick set block plane to remove most of the protrusion, a longer bed 5/1/4 plane to get it almost even, then a #4 smoother over the whole surface until the strip is perfectly flush.
At this point if there is some tearout to clean up, I scrape and sand the entire surface as it will be awkward to smooth after it’s sliced up into side pieces. I sand to 280 grit because I have a lot of 280 paper.
See the original “Woodwright’s Shop” video here.
This is a Stanley Miter Box, same as the one Roy uses in the Video. The huge back saw will cut just over a five inch depth. In the video, Roy holds the stock with his left hand but I had trouble with the board moving so I use a couple of clamps. The side of the stock with grooves and lip strip is always facing the Miter Box fence.
Here I’m making the first 45 degree cut on the leading end of the stock.
These boxes will hold 3×5 cards so I use a sample card to lay out the inside length for the second cut. It will be about an eighth inch longer than the card, and the mark is on the inside of the next miter. This will form the front of the completed box.
Now the stock is flipped 180 degrees and clamped on the right side of the Miter Box. The second cut is made just to the right of the pencil mark.
The future box front has been sawn from the grooved stock with lip strip included.
Fiip the stock back to the left side and trim off the miter from the first piece. This will be the first cut on the next section, forming the left side of the box.
How long should the box sides be? The inside edge of the two miters have to fit between 1/8 inch rabbits on the thin top stock. So I use the actual top stock to mark for the cut. Best to err on the narrow side here, as I can always trim the top stock a bit.
Remember that wood moves when humidity changes so the top has to be a little loose in the cross grain direction. This is actually “Frame and Panel” construction, the top and bottom pieces float free in their grooves.
The third piece sliced from the grooved board will form the rear of the box. Here I am using the front piece to lay out where to cut. I will actually cut a bit long and trim this rear piece to match the front later.
The fourth and final piece forms the right side of the box and follows the same procedure, matching length with the previously cut left side.
I put pencil dots where they won’t show in the bottom groove to keep track of the order the pieces were sawn out. Assembling them in order maintains the flow of wood grain around the completed box sides.
Later, I will use the dot method to keep track of the lip strips as they are pried out.
Now that all four sides are sliced out, I clean and trim each to exact size on the Shooting Board. First I use a utility knife to relieve the leading corner of the two exposed grooves. This keeps the plane from tearing out that delicate edge.
On the first (front or left side) piece it’s only necessary to take a couple of clean up strokes.
The mating second piece (rear or right side) is always sawn a bit longer than the first. It’s cleaned up and then trimmed until it’s length exactly matches the first piece. The photo shows the front and rear pieces back to back.
With all four pieces cut and tuned to length, the box can be dry fit with a couple of rubber bands around it, to check the miters.
These miters fit pretty good. If they were off, I would tune the Shooting Board miter attachment and re-shoot the miters. It’s adjusted by adding or removing strips of thin cardboard underneath. I use playing cards.
The technical term for this sideways holding fixture is a “Donkey’s Ear”. Having never owned a Donkey, I can’t comment on the name. It is simply a block of scrap cut at 45 degrees, and a thin bit of scrap screwed to the end for a stop. I glued sandpaper to the 45 degree face to help keep the work piece from moving around.
On a Shooting Board, the plane blade is vertical. It helps to get through the cut if the plane has a lot of mass so I use the big Stanley. Since it’s planing end grain, it must be very sharp and take a fine shaving.
The whole thing is clamped to a convenient massive surface (table saw).
See the original “Woodwright’s Shop” video here.
I remove the lip strips and set them aside. Each gets pencil dots on the bottom so it can be returned to it’s original position in it’s original groove. Dots are placed where they won’t show in the assembled box, bottom of the strip and lower half of the groove.
The jig I use to cut the spline grooves is discussed elsewhere on this BLog. Here the first box side piece is clamped in the jig by the bench vise. This particular board is warped slightly and won’t lie flat against the jig so I use a couple of F clamps to pull it tight. If the grooves are not cut consistently, they won’t line up properly. Have to make sure the F clamps don’t interfere with any part of the plow plane.
In the video, Roy knifes the sides of the uncut groove at the exit point to control tearout from the plow plane. He guesses where the groove will end up and misses the mark quite a bit. My solution is to set the plane on the jig, put downward pressure on the main skate, and pull it back across the work piece. This leaves a mark across the miter and you can clearly see where to place the knife.
Hold the knife perpendicular to the miter surface and cut down both sides of the groove an eighth of an inch. It doesn’t hurt to knife edges at the beginning of the groove also, where the blade is dragged back across on the return stroke.
At first I was still getting exit tear out at the bottom of the groove (and Roy does as well), so I made this little chisel from eighth inch key stock. It’s sharpened at a 25 degree angle.
I set this in the groove in the stop block and give it a tap with a small hammer. Now the wood fibers are precut on all three sides of the groove and most plow plane tearout is eliminated.
With the board secured and all preparation complete, the actual plowing of the spline groove commences. Even with the jig it takes a lot of discipline to keep the plane moving in a perfectly straight line.
The 45 is cutting across end grain so the cutter has to be as sharp as I can get it. I will hone it after every other box (16 grooves). Also at the beginning and when the groove is cut about half way, I stop and wax the outside of the skate with paraffin.
The reward is a perfectly executed groove 1/8″ wide and 1/8″ deep with no tearout on either top or bottom edge.
I’m making four boxes with this project, so 31 more grooves to go!
And they are now all cut! One finished box and three sets of sides ready.