Tag Archives: wood

Shadowbox for 7490 Clock

7490 TTL Digital Clock Housing

Projects, TTL Chip Clock, , , , , , ,

After a few months of testing ( April – June 2017 ) the 7490 TTL decade counter chip based clock out with the newly added OCXO it was ready to be mounted in a housing.

7490 TTL Clock with OCXO under test
7490 TTL Clock with OCXO under test

Monitoring it against an accurate timebase ( Linux PC with NTP ) while piled up loosely on a small table in the office, it was running good and steady. No flaky counts, no flaky digits that were not lighting or staying lit when they should not be.

 

 

 

Consolidating Power

After the photo was taken above,  the power supplies for the clock were consolidated. Under testing it was powered by 2 wall supplies, 5V for the TTL chips and 12V for the OCXO. For the final version I used a 7805 regulator on the right hand side board to down regulate 12V from a Radio Shack 12V/2.3A power supply to 5V for the TTL chips. I got lucky and spotted the power supply during the last few days that Radio Shack was still in business in April 2017.

Wood Housing

Not having a good set of tools on hand to build a metal housing, a good option was a  wooden one. Micheal’s craft store had both the base that the boards were mounted to and the shadowbox. Both were unfinished and reasonably priced, I believe $5 for the board and $12 for the shadowbox in 2017.

7490 TTL Clock Circuit Board Base
7490 TTL Clock Circuit Board Base
7490 TTL Clock Shadowbox, cover removed
7490 TTL Clock Shadowbox, cover removed. A bit larger than is needed but, it works fine. The glass cover was removed in preparation for sanding and the application of linseed oil.

The base was drilled out to recess fit 10mm standoffs. Holes were drilled for the M3 screws and then countersunk with a larger bit to accommodate the 10mm standoffs. Once again I made out good at the Radio Shack closeout and got a bunch of standoffs.

Subassembly

7490 TTL Clock Mounted on Base
7490 TTL Clock Mounted on Base

The clock mounted on the base in a state of readiness to drop into the shadowbox as a subassembly. This trick is a bit that I learned from working in manufacturing in the past. To make things efficient and serviceable it was common to mount boards on sub assemblies and then mount the subassembly into a piece of machinery.

 

 

 

7490 TTL Clock Mounted in Shadowbox
7490 TTL Clock Mounted in Shadowbox

 

Finally the subassembly gets dropped into the shadowbox and is held in place by four small wood screws that are on the back.

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7490 TTL Clock Final Housing
7490 TTL Clock, Final Housing

 

 

magnetic knife holder

Hard Drive Magnet Knife Holder

Projects, , , , , , , ,

Recently I finished a small project to make a knife holder for the kitchen. It was made using one small block of wood, some screws and 8 magnets that came out of dead harddrives. The magnets were bought in Ithaca, New York from the Fingerlakes Re Use center ( 2255 N. Triphammer Road Ithaca,NY in the Triphammer Marketplace, phone 607-257-9699). Fingerlakes ReUse rebuilds and sells used computers ( much more other items as well ) and they sell harddrive magnets for 50 cents each (as of Sept. 2015 ). They have a pile of these magnets and it is worth picking through the pile to get some flat ones, looking for matching pairs and ones that will take a #6 screw for a project like this.

Harddrive Magnet Knife Holder
Harddrive Magnet Knife Holder

For the knife holder, I used a piece of oak flooring 3/4 inch thick, 10 inches long. It is best to use a piece of thick wood, because when you pull the knife off, there is a tendency to pull from the bottom handle out, which tips the knife towards the cabinet as the bottom magnet releases first. If the wood was thin the knife point would tip against the cabinet.

I cut the tongue and groove off the board ( trims it to 2-1/2 inches wide ) and then sanded it a bit on a belt sander to make the edges a bit rounded. Then using a drill press, I drilled out the holes to take #6 screws, 16 for the magnets (#6-5/8 machine screws), 2 (#6 – 1-1/2 wood screws ) with countersinks for the mount points. The whole process took about 20 minutes. For finishing I used a bit of linseed oil on it and then left it in the trunk of the car so a week while it was sunny and hot allowing the finish to be “baked” good and dry.

magnetic knife holder drilled
Magnetic Knife Holder Drilled

Strong Magnets

The magnets are rare earth magnets and are very strong. Therefore the piece of wood has to be screwed in good or it will probably pull off the cabinet when used. One caution with these magnets is that they will pinch your finger if you get it between them and another magnet or anything else ferrous. When I was cutting the wood I put one of the magnets down on the table saw. The steel on the table saw is so massive that the magnet was hard to get off, I had to use a screwdriver to pry the corner up, I could not lift it with my fingers!

Knife Holder Mounted To Cabinet
Knife Holder Mounted To Cabinet