Some wood working

Pretty soon I plan to build two desks. One desk to replace a computer desk and another to be more of a work table for my “tinkering”.

The current computer desk is pretty much Jerry-rigged. Concert speakers as the legs and a old table top sitting on top. A while back I added a TV stand for the 32inch TV/monitor to the desk to get more space and added some poles on the rear corners to mount the speakers. It doesn’t look all too bad but I know the misses doesn’t like it all too much and when we move I doubt the computer would stay in the master bedroom so the current desk would be a eye sore if it was in say the living room area.

I would love a corner desk but the last time I had a corner desk it ate up too much space and once again the wife didn’t like it too much. So a simple desk with one or two drawers on the left and right side. Cabinets on both sides as well. One of the cabinets will house the computer and the other will have two roll-able shelves for the printers. I also need to incorporate a space for the router, modem and the phone ATA box. Maybe a “back splash” piece and mount the speakers too it.

Construction would be birch plywood and maybe some 2x4s. I’ll attempt to do pocket screws to hide the fasteners. The wife and I love the rustic look so a dark oak or english oil and plenty of polly to finish it.

The workbench desk will be super simple. A typical work bench is a bar height but typical desk height will do fine for now until I get a real work space. The desk will have two drawers on each side and open shelving to store part boxes. Might include a hutch with a tilted top shelf and cabinets. I will also have a back splash on this desk that will have a power surge strip on it. It would be neat to have the computer monitor adjustable so I can flip it or swing it in and out of the way. At the same time I want it simple enough that I can extend it in the future by adding a second desk or convert it to a corner desk.

Construction would again be birch plywood and pocket screws. To finish it I plan to use a very light oak color varnish and the rest would be a dark walnut or just paint it black.

I’ll take pictures of the builds and document the progress. I might also post plans for both desks.

Power supply update 29/16

I’ve been tinkering around with the power supply. I plan to add three LM317Ts in parallel to be-able to achieve a 5 amp output. I also found some beefy resistors to use for a built in adjustable voltage divider so I can have the ability to have a negative voltage rail. Only problem is I could only get a maximum of 14.5 volts on the output but I can have a different output channel.

Theory of a DIY Analog Curve Tracer

There is a super easy circuit for turning a Analog Oscilloscope into some what of a curve tracer, it’s called a Octopus. Nothing more then a low voltage AC line and a resistor to handle the current.

Now what if you don’t have a Oscilloscope let alone a vintage Analog scope? Well the Octopus doesn’t need much resolution to give you a signal on the device under test. Should work fine with a old CRT television.

There are plenty of guides on turning a CRT TV into a so called Oscilloscope. However they’re very basic and do not do much other then connecting a audio source or a function generator to it.

Now if we add a two channel Amplifier to the Horizontal and Vertical coils of the CRT we can then get a typical analog scope view. However this is very low resolution and you might be able to also add a Attenuator to the input. From the input you would add the Octopus circuit.

Using something similar to this diagram we could add a Sweep and Octopus and just tap into the coils. Instead of powering the CRT from this circuit we would only use the Vert and Horz coils.

circuit7ss

Instead of 240V on the B+ we would use a much lower voltage. Basically We would use the lower portion of the circuit and only need the X and Y channels.

We would also need this circuit.

circuit7ssoscope

This would add the Sweep for the horizontal.  From there we can add the Octopus.

Super easy minimal latching switch

For my power supply I wanted a momentary latching switch for controlling the output function to be on or off. I’ve tried a few circuits here and there and just didn’t fit the bill. Then it hit me, what about a Thyristor? Well sure enough it does the job and with only three resistors and two switches to control on and off. Granted it would be nice to have a single switch to control it but the nice feature with two switches is I can hold in the OFF button to make the circuit active momentarily.

I found a schematic with google images but it was a bit unstable so I tweaked it. I use a 12volt source to power it and added a extra 1K resistor the stabilize the current.

latchingswitch

The 1K isn’t really needed but for my needs it does since I have a N-Channel Mosfet working as a high side switch and a LED for output status.

Laptop from the grave

A while back I bought two IBM Thinkpad R51s from a local thrift store for eight bucks. They both had cracks on the casing and one was missing the keyboard. No hard drives or optical drives for that matter. I got one single working system out of the two however I didn’t have a power adapter for it and had to use my ATX bench power supply. Ran fine under 12volts but I couldn’t use a hard drive due to current restrains. Well I found a power adapter yesterday at the same thrift store. I tossed in a 60GB hard drive that was the only one able to fit from my collection and for giggles tossed on Windows 7 starter. Worked fairly nice so I updated it to Ultimate, however there is a huge issue. Driver support sucks for it. I tried using XP and Vista drivers but when rebooting it wouldn’t retain and revert back to generic or unknown hardware.

In the end I installed Debian 8 Linux. It runs fairly nice and all of the hardware worked out the box including the Wifi that I was able to install the OS with.

Some time I need to mix up some ABS glue and repair the casing to the laptop. When I finally do that I might go ahead and paint it.

Took the Harbor Freight Multimeter challenge

My current multi-meter has seen better days so I decided to buy a Cen-Tech 37772 Multi-Meter. It’s really a re-branded Mas-Tech meter. Have to say so far it isn’t that bad for a cheap meter. Granted it is no where close to a Fluke or a Agilent but it works fine for low DC voltages to give you a ballpark range. The Ohm meter function works well unlike my old meter that freaks out when I test a 1meg or higher resistor. The audible continuity is crap however. It sounds statically and isn’t really quick on a reading. The temperature only reads in Celsius. I didn’t bother with the “transistor tester” since they never work right on any kind of DMM meter that offers it. I haven’t tried the capacitance tester yet.

The meter doesn’t have a kick stand but the LCD folds out. Huge display but no back lighting.

In all if it wasn’t on sale I wouldn’t of gotten it. Does it compare to a True RMS meter. NO, but it works for basic ballpark ranges.

Power supply Update 17/16

Wish this project would come to a end but since I had to use a different case I pretty much have to rebuild it since I am using point to point construction.

Anyway, I found my collection of hole saws and added a cooling fan to the case. A small Ninec 20mm fan should be fine as a exhaust fan while the front panel has a open lip on the bottom for air to enter. I need to add some feet to the bottom of the case so that function will work correctly.

I thought the secondary second tap of the transformer was 5v in the last post but it’s really 12v. Just have to add a second rectifier and I can use that for the Fan and USB.

Power supply update

I attempted to make a clear acrylic case but screwed up horribly with it so I’m using a wooden box from a old speaker cabinet and a plastic front panel from a photocopier I bought a while back for the CNC project.

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Just a quick mock-up. I need to plastic weld or glue some patches and sand it. I plan to paint it black.

IMG_20160116_140227[1]

Nothing special  yet. I just mounted the transformer and heatsinks to the rectifier and regulators. The small PCB on the upper left is the USB. Next I need to add a fan for airflow. Since the transformer is a multitap I might use the 5v lead.

Making custom front panels

Making a front panel for a project case can be dawnting at times. Reason why is if you have dials, switches and even displays you want everything to fit let alone even and square. Last thing you want is a LCD to be offset and tilted.
I have found it best to use graph/grid paper. Tape or even glue it on the item you plan to use and draw away. With this route you want to draw everything in squares shapes. Just think of it as legos or minecraft and you are set. If you glue on the paper you can then drill or cut the panel with out measuring the center unless you want a rectangular shape. Easy fix for that is the use a straight edge and go corner to corner and where the line intersects is the center.
Here is the panel to my bench power supply. Just have to finish mocking things up and cut away.

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Bench power supply update

I ran into a huge snag. The strip board I got isn’t of any use. There are cracks in the copper runs all over the damn thing. So instead of a PCB I am going a bit old school and doing point to point connections. Now there was one slight issue. The TO-220 parts are kinda hard to do point to point but I got a idea. I attend to keep the Molex connectors from old computer power supplies. I have a bunch of the smaller floppy connectors. The TO-220 fit perfectly inside. To keep the wiring scheme from getting mixed up I removed one of the black wires and moved the yellow wire over. Also fan three pin connectors work well.

So far things are working out well.