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'.

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...

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!

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.

Audio attenuator

I know, I know - everyone is wondering when I'm going to pop a cap in the aerosol of Silly String. I'm still waiting for the Great Hairy Leader to lend me his vidcam. I want the best possible footage for your delectation. More news soon...

The project for March did actually take place. The Hairy One needed an audio attenuator to balance line-out from a sound desk to mic-in on his video camera, so he could record some live gigs without unwanted background noise. A bit of Googling turned up schematics for a suitable mono attenuator. The Secret Laboratory adapted the design to produce a stereo attenuator for the purpose, constructed entirely from salvage. This is recycling at its best.

The R1s are 10K and provide the bulk of attenuation. The R2s are 1K and serve to sink optional power from the camera input to ground, fooling it into thinking it really is dealing with a powered mic (you lose a bit of signal here as well but, hey, attenuator - there's a clue in the name). The C1s are 104 ceramics. You could use almost any similarly rated ceramic caps here - all they are doing is making sure that no DC power gets from the camera to the desk. This model provides approximately 21dB attenuation.

I really wanted to etch a custom board for this project but, when I sketched in on paper, it looked like three strips of Veroboard, so I built it on three strips of Veroboard.

I put phono plugs on the desk end (line-out) and a single 3.5mm stereo jack on the camera end (mic-in). Worked a treat.

I wanted to post a photo here but the device was needed on the night in question. I'll post a photo as soon as I get the device back.

Results for February's project

Thanks to everyone who responded. There were six genuine voters and two virtual voters. Analysing the responses was not as straightforward as I had expected.

Kate voted for option 3. Kate's cat also voted for option 3 but I suspect this was just Kate's way of trying to wangle some extra representation and so I'm accepting only the one vote (sorry Kate's cat).

Cosmic Tink Tank voted for option 3 and included some interesting suggestions to enliven the proceedings. I won't be using the suggestions but, hey, what a creative mind.

Mille Vache voted for option 2, which I would have been delighted to run with but unfortunately Mille rendered option 2 redundant by publishing the recipe in advance of project selection and execution. Never mind - it was a good service rendered by Mille and I trust everyone will try the recipe (I certainly will).

Angie voted for option 2 but see Mille Vache above. Sorry Angie. At least you've got the recipe now.

Andrew voted for option 2. Yep, that's right. Sorry Andrew. Blame Mille Vache. Enjoy the honeycomb!

Su voted for option 1. I am counting this vote as valid even though I know for a fact that Su is voting that way only to try to put me on the spot. You don't believe I can do this number theory stuff, do you Su? I have only one thing to say: Tom Westerdale, Birkbeck College. He taught me everything I know about number theory, set theory, logic and computability. Although I'm a wee bit rusty, I've still got my notes...

Anonymous voted for option 1 but then disqualified himself/herself by voting twice for option 1. A bit harsh maybe but Anonymous could be anyone - perhaps even Su trying to inflate her representation. Anonymous did almost redeem himself/herself by suggesting that option 3 would be more fun but, in all fairness, if I'm invalidating this person's vote for option 1 then I must do the same for option 3.

So there we have it:

Option 1: one valid vote (Su).
Option 2: three valid votes (Mille Vache, Angie, Andrew) but option rendered redundant by early disclosure.
Option 3: two valid votes (Kate, Cosmic Tink Tank).

A clear win for option 3. I kind of thought it would go that way.

And here you are - the very can that's going to get it. The contents conform to European directives 76/769/EEC and CE 3093/94. I'm not saying that's good and I'm not saying that's bad but one way or another it will do no more harm to the environment than if it were deployed more conventionally, at a party for instance. The only difference is that my special party will be over in seconds. The only way to reduce impact is to ban this stuff altogether and that would probably be a good thing.

When is it going to happen? Well, I had planned on doing the deed later today but a friend of mine offered the use of his professional quality video camera in place of my humble mobile phone video capture facility. I must admit I couldn't resist the opportunity to capture some high-speed vid and render it in slow-mo for your delectation.

Do not try this at home. See you in March!

Your chance to vote on February's project

February has been a slow month for the Secret Laboratory. I have several serious projects on the go but there will not be any results until late March at the earliest. Therefore, as infill, I have decided to test the intellectual orientation of my readership. You may vote upon the following three last minute projects for February, the most popular of which will be published here.

1. Decidable Predicates. How to decide whether numbers possess a given property.
2. How to make that yummy honeycomb stuff they put in Crunchie bars.
3. What actually happens if you shoot an aerosol can of "Silly Party String" with an air pistol.

You may vote 1, 2 or 3 by responding to this post.