Saturday, January 15, 2011

shed PC cabinet, and electronics test gear

another set of projects!!! - Yes I know - got more than enough on my plate as it is, but it is related (see end of this post)

I needed a PC in the shed for programming work. Given the lack of space, the easiest thing to do was put the PC in a wheel-able cabinet, and packaged in such a way to permit it to be collapsed as small as possible.

I'd rescued an old 3M overhead projector a couple of years ago, and the wheeled stand it came on... This stand, with a few modifications, became the PC cabinet.

The original stand had a top which was set approx 6" (150mm) under the level of the top vertical posts, and the 2 flip out leaves attached to the posts. I raised the top shelf to line up with the posts, and then closed in the underside on 3 sides with some old sheet metal.  I took another piece of metal to work and bent it up to make a door for the fourth side.

The "front door" of the PC cabinet is the grey sheet of metal on the RHS of the picture - with black cloth tape covering the cut edges for hand protection.

The above photo shows the LHS leaf in the raised position - whereas the other photos in this article show both as lowered.

The PC is an antique (old celeron from memory) but it does what I need (runs the PICAXE suite of software). Network is accessible (if I run out the 15m patch lead) and the speakers, mouse and keyboard cabling is wrapped in a spiral wrap and pinned under the top shelf.

Currently (due to other projects) the most this PC does is play music for the shed area - the programming has been on hold for a few weeks now due to other commitments.

As part of the PICAXE work, I needed to rig up a 5VDC power supply for the breadboard and other circuit prototypes. Digging through my boxes of salvaged gear I found a near new 5VDC SMPSU. Using some scrap pexiglass, I fashioned up a board with the SMPSU encapsulated at the top. The scrap pexiglass had some bends in it already, and I used them to form the cover for the 240VAC section, and to mount the power switch.

It was a simple case of then bringing the 5VDC and COM rails out to the prototyping area by means of the terminal block. I also brought the mains Earth out as well. The colour code for the terminal positions is shown on the LHS of the cover.
LRF are applied on the bottom of the unit to stop the fixing screws from scratching up the top of the cabinet.

The unit fits nicely in the box with the other electronics bits.

I needed something, and I was so out of date with my previous experience (6502, 8086, pic16f84) that I asked on the newsgroups what was the best to come back in with... the suggestions included Arduino and other systems, but PICAXE came through loud and clear as suited for what I'm trying to do...
I've a project to help someone who's eyesight is going. He's a machinist who's finding it hard to use a standard dividing head - I can't afford a "DivisionMaster" (excellent product designed by Tony Jeffree) so I'll try and build my own version (with several features not in the original - suited to the user's tasks) and bring my skills back up at the same time.
That is the story of my life so far - get an idea to do something, identify pre-requisite equipment and skills, acquire those, find there are more needed, etc ad nauseum.
Kinda the model engineer creed - "Build a jig to build a tool, to build a jig, to build a tool, to build a jig to build a project". In my case the lathe was bought to build a micro hybrid rocket motor, but the lathe needed parts so I started building parts, which meant I needed the furnace, which meant I needed to learn.... and on the story goes.
Don't take the above as a complaint - by the time I build that motor I'll have a fully equipped workshop, an amazing set of skills, and a very diverse set of experience - all I need is time... and patience... and space for junk... and money for bits...       :)

welding helmet renewal

I learned to weld (SMAW - aka Arc welding, aka "Stick welding") with a standard CIG "rockhide" full face helmet. You had to flip the helmet up and down to see whenever the arc wasn't running. Better than the handheld mask I used a few years later, but still painful to use compared to the newer "speed glass" style auto-tinting helmets. It's so much easier to weld when I can see the tip of the rod moving up to the point of the weld, instead of losing sight of it due to flipping the filter down

I bought a cheap helmet and used it for several years, and eventually it stopped working. Being the tinkerer that I am, I opened up the main unit and discovered a few things...

The helmet has a solar cell on it, and was advertised as never needing batteries since it charged from the sun. The batteries inside were 2 silver oxide non-chargeable button cells. My guess was that the solar cell reduced load on the batteries, but was never able to charge them. (Silver oxide batteries aren't rechargeable)

The other finding when I opened up the unit was that the nominal 6VDC across the 2 batteries was only 2.8VDC... I can hardly complain since they lasted seven years.

The rest of the circuitry is under the white "potting" used to protect the circuitry - I never disturbed that, just accessed the silver terminals which used to be spot welded to the original batteries.

Armed with that finding, I quickly fashioned up a 6VDC supply and connected it to the original battery leads (with the old battery removed) and tested the helmet - it worked.

The photo above shows the hole drilled through the back panel of the glass unit, and some flexible Cat5 cable led through for accessing the power terminals of the electronics.

A more permanent solution was made up...
The battery holders are from some cheap solar garden lights the dog broke
The cable is some flexible Cat5 patch cable
A number of holes were drilled in the helmet to affix the battery holders, and cabling.
All holes were then sealed over with some hot-melt glue, and painted over to block the UV from the welding operations.

Problems found with this solution:
Firstly the weight of 4 AA batteries sitting at my mouth level caused the front of the helmet to always hang down - rendering the friction locks at the headband useless - I ended up resorting to a short length of cord which runs from the top of the helmet to the back of the headband to stop that
The other issue I found was the attempt I made to have the power "switched", and removable - the 2 automotive crimps - frankly they proved more trouble than benefit. I'll cut them out and replace them with a soldered joint.

What else do I know about these units?
They don't like being dropped in quench buckets full of water
They don't like sweat dripping into them - day after stinking hot day
They can be replaced for around $30 via ebay (6shopriver is an example seller - no connection)

I don't consider the repairs I made to be a waste of time, they bought me some time so I could finish the job until I could replace the failing helmet. I will fully repair this helmet if possible and keep it as a back up.

shed tips - foaming tools, and disposable nozzles

Foaming tools

Basically a number of tools come in either blow-mold cases, or metal cases with blow-mold inserts. The decision to use blow-mold is based on providing a close fit to the tools in the case, without the cost of the old style wooden inserts.
There is a problem with the blow-mold inserts - breaking down due to age and vibration. the plastic liner breaks down and cracks apart due to the weight of the tools and eventually becomes useless.  Following the advice of those wiser people, I take the time to fill the backs of blow-mold liners so there isn't as much "give" in the liner, and the tools don't break it down as much (if at all)

The basic principle is to fill the voids in the back with something disposable and durable - currently I use expanding foam (the single expansion type, not the one which expands again when contacted by heat or water), but in the past I've used silastic (caulking sealer) bulked up with either sawdust, or scraps of foam, wood, or even general shed rubbish (broken hacksaw blades, etc)

Using foam
Access the underside of the blow-mold liner

fill the gaps with expanding foam

apply a sheet of heavy card (old filing cabinet suspension files) and weight it down until the foam cures

if you remove the card,you will find the foam pretty much filling all large gaps, but maybe missing some of the smaller ones - sometimes I refill them, other times simply leave them.

The photo below shows one weighted down liner, the other simply left uncovered and unweighted during the foam cure

As seen below, the unweighted one cured with large air bubbles under the foam, basically providing no support to the liner and the tools. The cut way pieces of cured foam aren't tossed away, instead they are pressed into the gaps, then refoamed and covered and weighted. As mentioned at the top of the article, the filling doesn't need to be anything flash, so offcuts of foam work fine.

I know people who use plaster for this some task - works well - my only concerns are the weight, and the holding of moisture inside the tool case.

Disposable nozzles for foam dispensing
The foam dispensing can nozzle - the sales guy from ramset told me that the expnding foam valve is a single function unit as mandated by the nannygovt  - as a result I buy my can (local trade store) and collect up a handful of straws from macdonalds. I cut the supplied nozzle tube at 1" (25mm)

and slide the macdonalds straw over the original (shortened) nozzle tube - this makes cleanup much easier (throw the straw away, and blow out the short piece) - As long as I schedule all my foaming for one day, I can usually use up the whole can before the internally sabotaged valve locks me out of the can.

Upcoming posts -
New life for an old welding helmet, and the lathe stand/cabinet