Archive for May, 2015

Toastmasters Timing Light

There was a post on the Workshop88 mailing list asking for someone to construct a small manual light box for use by the timer at Toastmasters meetings. The specification was, a switched Green LED, switched Yellow LED, switched Red LED, and a fourth switch to blink all the LEDs at a 1 hz rate. The actual timing is done by a human with a stopwatch, the box just signals the speaker. The Toastmasters’ existing setup uses 110 volt incandescent lamps and is not very portable.

Much discussion ensued on the mailing list about what could be done with a Raspberry PI or Arduino, LCD screen, etc. etc. but in the end, I agreed to design and build something simple according to the original manual spec. Ultra bright LEDs could be used with a 555 timer to do the blinking. A standard MN1604 9 volt battery would easily power the LEDs for 8 – 12 hours. And I could use the standard Arduino style enclosure: and Altoids tin.

I’ve built two of these boxes. The photos on this page are from the second – but first came a prototype on a solderless breadboard.

Breadboarded Timer

Breadboarded Timer

 

On the breadboard the timer circuit was checked for reasonableness and LED illumination tested. I found with a nine volt battery I could put two LEDs in series, and with a 200 ohm limiting resistor the Red LEDs drew 15 milliamps, the Yellow 20 Ma, and a pair of Greens 12 Ma. The Red and Green were very bright, Yellow not so much. Later I checked the spec sheet on the Yellow LEDs and found they would take 50 milliamps.  I lowered the Yellow limiting resistor to 130 ohms which brought the Yellow current up to 35 Ma and then all three pairs were similarly bright.

These Ultra Bright LEDs have a clear plastic envelope with a lens formed in the end which directs most of the light straight up.  I sawed the tip of each LED off at a 45 degree angle to remove the lens. This directs more light to the front and reflects much more to the rear.

Original and Faceted LED

Original and Faceted LED

 

Here is the final schematic. This is slightly revised from the first model, the timing person wanted a separate power switch, and also wanted the blink cycle to start with LEDs on rather than LEDs off.

Toastmaster Timer Schematic

Toastmasters Timer Schematic

 

The original breadboard had all three of the grounds at the bottom of the 555 chip connected together, a switch from there to power negative activated the 555. In that configuration, the 10 microfarad capacitor started out in a discharged state which resulted in LEDs off.  Splitting that capacitor off and hard grounding it causes it to start in a charged state which turns the LEDs on. Switching the 555 pin 1 to ground starts the blinker.

I constructed the 555 module on a bit of perf board with copper pads on one side. A six hole by seven hole piece holds all the parts. This is the layout sketch I used.

Toastmaster Timer Blinker Module

Toastmasters Timer Blinker Module

 

Here is an assembled module. It measures 3/4″ by 5/8″.

Blinker Module

Blinker Module

 

With the blinker built and tested, I turned to physical construction of the box. Everything should fit in the lid.  I made an aluminum template for drilling the ten holes. In this photo, the four switches have been mounted and there are small holes drilled above the nut for the anti-rotation washer.

Altoids Lid Drilled and Template

Altoids Lid Drilled and Template

 

The LEDs don’t have any formal mounting hardware. To get maximum exposure, they are just inserted in the holes until they bottom out on the shoulder. Then a narrow strip of FR4 perf board is threaded over the leads. This photo is three strips cut from a wire wrap prototype PC board. I use a crosscut sled on a table saw for this, with a narrow carbide blade centered on the fourth row of holes.  Width of these strips is important because they help restrain the battery.

LED Retaining Strips

LED Retaining Strips

 

The fiberglass PC board strip is tacked down with bits of bent paper clip soldered to the tin lid. That paper clip in the center had to be moved later because it interfered with the battery. Soldering the LED leads in the perf board creates a very rigid assembly. I added the current limiting resistors between the LED pairs.

Switches Mounted and LED Dropping Resistors

Switches Mounted and LED Dropping Resistors

 

Spacing between the switches and the LED retaining strip is critical because the nine volt battery has to fit there, but not rattle around. A large paper clip was straightened out, then bent to capture the battery. A paper clip has just enough spring to hold the weight of the battery. This photo shows the battery clip soldered onto the lid. White arrows point to the four Z shaped wires holding the LED retaining strip in place. Ground leads are soldered to each switch and each has been cabled to it’s assigned LED pair.

Pins Holding LED Board

Pins Holding LED Board

 

Here is a photo with a battery installed in the clip. You have to be careful not to short the terminals on the lid lip.

Fitting the Battery

Fitting the Battery

 

At this point the lid is ready to receive the 555 timer blink module. It is mounted with two more bits of soldered paper clip, this time bent into an L shape. One clip is soldered into the ground hole of the perf board, the second in a vacant hole. White arrows in this photo point out the two module mounting clips also three of the LED restraining strip clips. Note the two retaining strip clips nearest the rim are bent parallel to the lid edge. This is to give clearance for the box bottom.

Blinker Module Installed

Blinker Module Installed

 

The last piece of hardware installed was the power switch. I used a small slide switch as that type will be less likely to accidentally turn on in somebody’s pocket.  Two eighth inch holes were drilled, then squared up with a small file. I soldered the ears of the switch to the inside of the box.

Power Switch Soldered In

Power Switch Soldered In

 

Finally the wires for power were added, everything tested, and all loose wires laced up with waxed dental floss. A bit of foam tape was added to the bottom to help make sure the battery clip doesn’t come loose. There’s a small paper clip loop soldered next to the power switch to take up strain on the wires there.

Internal View

Internal View

 

Here is the finished box with all three LED strings lit.  Note this is not a normal condition, only one color at a time should be on, mostly the Green which only draws 12 Ma (but is so bright it hurts your eyes). Blinking will draw about 60 Ma half the time. Duracell’s data sheet shows a useful life greater than 8 hours with a 50 milliamp draw so I expect this application to last considerably more than that.

Completed Toastmaster Timer

Completed Toastmasters Timer

 

This has been an interesting project that was well received by the users.  There is a short video on my Dropbox account.

Added: May 27, 2015

I needed a way to get consistent bevel cuts on the modified LED lenses using my bench grinder which is far quicker than the Dremel tool with cutoff wheel method.  The solution as any woodworker would know, is to make a jig. In this case though I was able to re-purpose a fixture I made years ago to hold hand plane irons while touching up the bevel. It’s just two pieces of 3/8″ x 3/4″ steel bar stock with half a dozen holes drilled. One piece is tapped, screws through the other then clamp the plane iron in the jig and it can be held tightly to the edge of the grinder’s tool rest.

Adapting this fixture to hold LEDs only required adding a washer slightly thicker than the LED wire leads to one end. I had to grind the underside of the threaded bar to get clearance for the grinding wheel. Two LEDs can be slid into the beveled end and clamped there by the screws. A single long screw through one of the threaded holes at the washer end provides a stop that can be held against the grinder tool rest.

LED Grinding Fixture

LED Grinding Fixture

 

I can tweak the grind angle by adjusting the tool rest, and a few passes across the grinding stone produces the consistent bevel I wnt. Just have to be careful not to grind away too much. I put a dab of nail polish on the ground surface to clean up the scratches.

 

 

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Home Made Iambic Paddles

I have two homemade paddles to use with the Iambic Keyer Project.

This first example was made in the late 70s or early 80s, can’t remember exactly. I mentioned to a friend who worked in maintenance at a steel mill that I was looking for a heavy piece of metal to make paddles that wouldn’t scoot around on the desk.  We discussed some ideas and a few days later he produced the frame (all the blue parts) you see in the photo. It weighs over five pounds, it only moves if you want it to.

The arms are plexiglass fastened to short pieces of tubing. The tubing is flared at each end and each flare receives a bearing ball. Cup tipped Allen screws in the top frame and in the base capture the balls. With careful adjustment leaving a small amount of play, these bearings work well.

The rest of the paddle hardware is made of scraps from my junk box. Simple contacts made from machine screws work, but are noisy. Noise however does not bother the keyer much, as once an element is started, the paddle input is effectively debounced by dot/dash timing in the software.

Paddles Home Made About 1978

Paddles Home Made About 1978

 

My second example was made recently. I decided the blue paddles were not portable enough so I made something smaller. This set has a base of two inch steel Aux Bar scrounged from a telco installation project. The next photo shows the first iteration.

For pivot bearings I used brass thread inserts from Woodcraft. They have a 1/4-20 inside thread and a very coarse outside thread, intended to screw into a woodworking project. I filed the coarse threads off two sides of the inserts and soldered them to a strip of PC board material to form the paddle arms. The bearing for the arms is then the threads of the screws which go into threaded holes in the base plate.  Contacts are bent paper clips screwed to half inch nylon standoffs.  This works but has a terrible feel due to slop in the 1/4-20 threads.

I put a square of sticky silicone mat under the base and it stays put pretty well. The square was cut from a large mat intended to hold a wood work piece in place while you use a router on it’s edges.

Paddles Home Made February 2015

Paddles Home Made February 2015

 

The second iteration of the Aux Bar paddle is an attempt to remove some of the annoying backlash in the screw thread pivot bearings. I thought longer threads would help and got two threaded sleeves from the hardware store. These are made for joining two lengths of threaded rod. They have a #10 thread and are about an inch long. Two new paddle arms were constructed, this time with the bearings on the outside of the PC board as the sleeves are larger than the brass inserts used in the first model.

I inserted three sets of small screws into the arms to capture the tension spring which allows some adjustment. The spring shown in the photo is from an old IBM keyboard. If you part out one of those old Model M’s you have enough springs to last a lifetime. A second spring directly between the pivot points takes up some of the backlash remaining in the threads. Also the two #10 pivot screws are epoxyed into the base to eliminate that small bit of wobble. At the back of each arm where the paper clip touches, I added a drop of silver containing solder to make a better electrical contact.

This iteration has a very light touch but still too much slop in the bearings. I think with some tuning of the springs it will be very usable.

Paddles Home Made March 2015

Paddles Home Made March 2015

 

 Update 5/11/2015

Added a spring directly centered between the two pivot points. This spring is stronger than the small one separating the paddle arms, and it’s function is to take up backlash in the sloppy threads on the cheap pivot screws. I soldered cut down copper carpet tacks to the inside of the paddle arms to keep the new spring in place. The spring force is directly between the pivot points, so it does not contribute to the effort required to close the paddles unless you press hard enough to overcome it’s higher tension. It improved the feel of the Aux Bar paddles a lot.

Pivot Spring Added

Pivot Spring Added