Friday, 23 April 2010

Hacking the Jackhammer

"Oh, you mend things don't you? Would you mind taking a look at..."

My heart always sinks when this question is asked. Often I arrive to be confronted with a heap of '30s-'50s electrical junk with that tell-tale patina of flaking varnish and oxidised metal, only the protective film of sticky kitchen grease having secured its survival into the 21st century. There's a smell about that junk as well. It's the smell that says "Plug me in and you're dead".

What a delight then to discover this little gem amongst a heap of junk:

A classic musical effects pedal, all that is wrong with this baby is that two of the spindles are bent and the knobs are missing. Rated 9v, I ain't gonna die through messin'.

Sunday, 11 April 2010

The strawberries are safe - for now...

Further to a previous posting this month, it was a nervous moment when we modded the Davis Vantage Pro 2 environmental data logger last week. It's always a nervous moment when you try to mod a largely surface-mount motherboard with a clunky old soldering iron better suited to soldering cables to plugs. So many tiny, delicate components, so close to the heat source...

Battling with what surgeons call "intention tremor", we successfully removed the integrated antenna and replaced it with a socket, enabling Dr. Alcock to experiment freely in his role as Time Domain Reflectometrist for the Strawberry Farm.

Plugging a new (external) aerial into the socket, the first thing we noticed was a marked improvement on signal strength, the device pulling in data from the three remote stations with no problems. Davis note: you should be supplying these devices with an aerial socket instead of relying upon some c**t with a soldering iron to do the job for you!

Notice the signal strength from one of the remote stations - 42 (ringed red). That was previously about 30 with the suppled integrated aerial. Now we have a socket, Dr. Alcock will be experimenting with new aerial designs to drive that figure even higher.

The Secret Laboratory - not just about dicking about in sheds. More news soon...

Tuesday, 6 April 2010

Stereo to Mono converter - how to do it properly

On occasions you might wish to feed a mono PA input from a small stereo device such as a personal MP3 player or cassette player.

Historical note for youngsters: cassettes are those little plastic boxes full of brown string that your parents keep in cardboard boxes on top of the wardrobe. The de-facto standard of 129 metres of brown string wound on little bobbins is almost but not quite enough to store one whole album. This is what passed for copy-protection in their day. Left in a car for five summers, all cassette recordings of any kind evolved into either Wings or Steeleye Span anyway. This phenomenon has never been fully explained but is thought to be an early experiment in what is now known as consumer subscription expiry.

For example, you may wish to provide some recorded music during the interval between sets at a live gig, or you may be a quizmaster or quizmistress delivering the "music round" at your local pub. Either way, the material is on your personal device and you want it to go front-of-house, through the desk or whatever.

I know what you are thinking. You go to your local electronics store, you get a 3.5mm to 3.5mm stereo extension cable and a 3.5mm stereo to 1/4" mono converter and the job is done. Oh ho ho! No. You risk (at best) distorting your sound or (at worst) frying your kit. That's your decision but here at The Secret Laboratory we like to do things properly.

Here's how to do it properly:

Find a 3.5mm stereo jack plug, a 1/4" mono jack plug, a length of shielded two-core audio cable, two 10K resistors (brown-black-orange) and some insulating tape or heat-shrink tubing.

Solder all the bits together according to the following schematic and following instructions:

On the left, your 3.5mm stereo jack. Source (R) will probably be a red wire - connect it to the "ring" on the jack (you may need a meter to check which tag is the ring but it's usually the tag on the right as you look from the rear of the plug - red ring right is how I remember it). Source (L) might be blue, white or some other colour. Connect it to the "tip" on the jack (usually the left tag as you look from the rear). Connect the shielding (Source G) to the "sleeve" of the jack (that's the BIG tag that also serves to secure the cable when you crimp it). In this particular application it doesn't actually matter if you get the L and the R mixed up but it's good to get it right. Don't mess with the G though, else you'll be pissing signal to ground.

On the right, your 1/4" mono jack going to your PA. Connect the red signal wire (Source R) to a 10K resistor and the other signal wire (Source L) to another 10K resistor, making sure the two wires don't short at this end (that's where the insulating tape or heat-shrink tubing comes in handy). Twist the other ends of the resistors together and connect them to the "tip" (PA Sig) of the mono jack. Connect the shielding (Source G) to the "sleeve" of the jack (PA G) and crimp to secure the cable, just like you did at the other end. Get this right and the whole assembly will fit inside the 1/4" jack housing. Oh, er, now is a REALLY bad time to remind you that you should have made sure the plug housings were already on the cable - I'm sorry I'm sorry I'm sorry...

Right! You have just constructed a simple "audio mixer" - tell your friends! They'll think you're some kind of electronics genius! "Buy an audio mixer? No, I just make my own - it's nothing, really..."

Or: "Yeah Brett, I'd love to come to dinner tonight but I'm, like, building an audio mixer?" Think of the potential to keep 'em hot!!!

I showed my version (above) to Steve Glennie-Smith (Electronics Engineer par excellence) last night and he said "That's quite neat - for a programmer". Praise indeed!

Thursday, 1 April 2010

The importance of antennas

No, not "antennae" - that's what insects have. Antennas, as in aerials. Sticky-up or sticky-out bits of wire that mysteriously capture signals from the thick soup of radio-frequency data that's whizzing through the ether as we speak.

Perhaps you've got a long-forgotten Yagi in your loft or strapped to your chimney. A sat-dish on your wall or whatever. How soon we forget the importance of these humble items of hardware, yet we are becoming ever more reliant upon wireless communications technology.

Let me really drive this home with a concrete example:
  • No antennae, no automated irrigation systems.
  • No automated irrigation systems, no strawberries.
  • No strawberries, no Wimbledon.
You see? Tennis itself relies upon technicians willing to spend hour after hour experimenting with bits of bent wire.

Yesterday I visited the home of the perfect strawberry with a view to helping to create the ultimate wireless irrigation management system. Dr. Alcock's technical expertise combined with The Secret Laboratory's 40 years of soldering experience is certain to secure the future of UK sporting excellence for years to come.

Watch this space.