Miniature playable synth

While waiting for the boards from PCBCart to arrive, we decided to look at other miniature instruments for the range.



Of course we'll need a miniature drum kit, for laying down the beats, and a bass guitar for laying down the grooves, will be more-or-less the same as a guitar (same functionality, maybe a bigger beefier shape). We've already made up a simple drumkit prototype, using some piezos and an existing miniature drumkit bought off eBay.



the gold coloured disks mounted under each drum skin are piezo tranducers, connected to digital inputs on the PIC microcontroller



What we need now is to manufacture the 'kit from scratch, now we've proved that the concept works. That can wait until we're visiting the local hardware store and can investigate the diameter of different plastic tubing! Another instrument we've yet to have a go at is a miniature synthesizer. There's a debate about which style to do first - a Moog, a Roland or a Yamaha Keytar?



At the minute it's not important - we're focussing on the functionality; the enclosure can be designed later! Here are some photos of the early synth development....







Rather than mess about with hinges and moving parts, we've just made the keyboard out of a series of "sprues", connected to a thick bar along the top. The idea is that there should be enough flex in the acrylic to allow the user to press the acrylic keys onto a series of soft-touch tactile push-buttons mounted onto a PCB underneath. These key presses will simply be digital inputs, allowing true polyphonic sound to be achieved.



Our miniature synth will have 17 keys, starting at middle C.

Why seventeen keys and not any other number? I wish I could say it was because of the number of available inputs or some other technical reason, but the truth is we all watched classic 80s synth clips on YouTube and after seeing how to play Axel F decided that 17 was the minimum number of keys required!







Whether the 18F2455 will have enough inputs for what we're trying to do (there will be other buttons such as pedal sustain, LED outputs and so on) or whether we'll need to move up to the bigger 40-pin 18F4550 still remains to be seen.......

Robo-roundup #25

This weeks roundup will feature only three robots, but we do have another interesting post some very cool robots!

1. This robot may be able to run faster than you: http://spectrum.ieee.org/automaton/robotics/humanoids/mabel-bipedal-robot-is-now-fast-enough-to-catch-you

2. These two bots are the futures servant robots: http://spectrum.ieee.org/automaton/robotics/diy/pr2-and-turtlebot-team-up-to-bring-you-drinks

3. New hexapod roots plays the piano: http://spectrum.ieee.org/automaton/robotics/diy/hexapod-robot-plays-beethoven

Well, I hope you enjoyed this weeks roundup!

PCBCart order is in

We've found making consistently good double-sided PCBs quite difficult of late, especially when we're working with tiny 0.20mm traces (normally we don't go lower than 0.5mm to ensure a good trace even if the etching goes a bit awry).



Having designed the PCBs for both guitar body and neck, we spent some time looking at different providers and suppliers. There are plenty of people on eBay offering PCB manufacture and we've already been in touch with quick-teck.co.uk.



Matt from BuildBrighton suggested PCBCart and in the time it's taken other PCB manufacturers to respond to an initial request for information, these guys have built gerber files from a simple design, debugged it, confirmed and organised all the silk-screening and solder-masking and submitted the plans for manufacture.







Their response times are amazing.

I was given the task of investigating PCBCart. I posted my order to them at about midnight and went to bed. The next morning there was an email from PCBCart asking to confirm a few things - after I emailed, I got a reply within minutes (not hours or days like other fab-houses) and in less than 30 minutes and a flurry of emails, the boards were ready for production!



I was really impressed with their service and how quickly and keen they were to get everything sorted out. After filling the online quote/order form out (they even accept PayPal) and paying a rather reasonable �140 for 200 pieces, our boards are in production and we hope to have them in about 12 days. If the quality of the manufacture matches their customer support, we should have some fantastic PCBs in less than two weeks - it's taken longer than that for some of the other manufacturers to respond to our initial query.



Hopefully that will be the last piece of the miniature guitar puzzle in place and we can start assembling them for real!

More laser cutting magic

In a desperate attempt to prove to a friend that our laser cutter (see, no longer the spanky new laser cutter - how long did that take?) is more than just a big "boy's toy" I had to find something useful to make with it.



Unfortunately, a kit of parts for a CNC pick-and-place machine (our next major project) is seen only as yet another "boy's toy" and doesn't count. Neither does anything involving gears, cogs, or PCB enclosures. Clocks only just count, but we've already made one of those, so need to come up with something else. Something that appeals to non-nerdy people.....



Here's what I came up with.

Funky vibrant herb markers.







No seriously, a range of herb markers in bright funky colours.

Not only do they brighten up the garden (useful if you're a crap gardener and all your flowers die off early) and serve a useful function (telling you what should be in place of that patch of bare soil) they're frost resistant and easy-wipe clean. The perfect "gardening solution".







The problem, of course, in designing the entire set of six in one laser cutting dxf file, is I've now got a spare five sets in various colours. And a whole load of little tiny acrylic letters! Look out for "funky vibrant herb markers" on eBay soon!

Soldering 0.025" pitch cable

Our miniature guitar project uses a double-sided PCB for the fretboard which needs to be connected to the main board using a ribbon cable. We've tried "regular" IDE cable, but had trouble with the multi-stranded cores (they spread during soldering and can bridge with the wires/pads next to them).



Also, using 0.5" pitch IDE cable, the base of the neck-PCB needs to be quite wide to accommodate all the pads. Then we discovered some 0.025" pitch, solid core ribbon cable which seems perfect for the job.



Except, of course, that it's an absolute nightmare to work with.

Just look at how small this strip of 8-way cable is!







Although we have managed to make some workable guitars, each one took a loooong time to complete, and wouldn't be suitable for making on a regular basis. We've pretty much got assembling of the SMT boards down to quite a quick and simple method, using the solder-paste-and-hot-gun approach of assembly. Although fiddly, it's much quicker than using through-hole components.



We're still looking for a quick and simple way to connect our guitar's "body" and "neck" PCBs together. If there's any way we can quickly and repeatably solder this tiny cable to the PCB edge connectors, the electronic design will be complete, and we can put an order in with either quick-tech.co.uk or maybe PCBCart



We made up some test boards, to practice using different techniques for soldering the ribbon cable to the edge connectors. These boards don't actually do anything but allow us to practice connecting ribbon cables







With previous attempts at soldering this tiny pitch cable, we've had problems with it moving around as the solder paste melts and pulls the cable cores onto the traces. Holding or taping the cable to the bench causes it to lift up at the end touching the PCB which makes soldering particularly different. So before soldering, we prepare each ribbon cable:





the tiny bit of cable that will be connected to the board is trapped under a spare piece of PCB/copper clad board



After stripping and trapping one end of the ribbon cable, the remainder is bent vertically upwards and pinched between a second board to make a sharp crease...







...then bent along a second piece of board, away from the trapped end







The result is a "kink" in the cable, which allows it to lie flat along the bench, while the exposed fingers of wire sit perfectly along the PCB edge



Those horrible dirty fingernails are because they've been scraping solder paste off the kitchen table before anyone else noticed!



Using a small soldering iron we managed to solder an example bit of ribbon cable by applying solder paste onto the board and heating it with the soldering iron tip. The result was a technique that worked, but was very fiddly and difficult to do well. The solder paste bridged across the traces and was difficult to remove. Touching the soldering iron between the traces did remove the bridging, but in a lot of cases, also disturbed the other cores and bent them so they went out of alignment with the traces on the board.



So we prepared the board to try the hot air gun method of soldering







This was less successful than the first attempt!

The hot air caused the cable casing to melt. As the plastic melted, it caused the cable to buckle and lift off the PCB edge. With a bit of re-working, we got this bit of ribbon cable connected, but it too was tricky to achieve.







The final method of soldering was the "traditional" approach and worked the best of all (the latest cable is the one on the right with hardly any solder visible). This involved tinning the solid-core strands, placing them onto the PCB traces, then lightly touching each with a soldering iron tip. In this case, a larger tip works well as it joins two or three cores at a time.



The end result is a cable that is attached with very little excess solder and no chance of bridging. Soldering is as simple as holding the tip in place for a second or two. It's by far the easiest method so far for connecting the ribbon cable to the PCB.







The only downside is the preparation of the ribbon cable and tinning the individual strands. Using even a small soldering iron tip, this was fiddly and it took a few goes to get all strands tinned without any bridging between cores.



One solution may be to use a "solder pot" for tinning the wires.







Videos on YouTube suggest this may be the case:





So now we've got a solder pot on order from dealextreme.com. It'll be a few weeks before it arrives, but with a bit of luck, we'll be able to quickly tin/solder all 13 cores with a single dip - the plan being to batch-prepare a load of ribbon connectors and tin them all in one sitting. The solder takes about 10 minutes to heat up to a usable temperature so we don't want to be doing this for just one cable at a time!

Videos on bots #4

This week's videos on bots features some very cool robots, so keep on reading to see them.

This robot is called the HPI-G robot dog, and its obviously a robot dog.

This videos shows a swarm of robots interacting with each other.

This videos shows a new Japanese nurse robot.

We probably all know the cute little android robot, but this videos shows the real one.

This robot is called the "Wowwee Robaboa" and its basically a robot snake.

Thanks for reading and check back next week for yet another "Videos on Bots."

Hot air soldering - it's like magic

Here are some before and after photos of our recent hot air soldering.

These are tiny SOT-23 package darlington transistors.

A blob of solder paste was put on each pad (manually using a small paintbrush). As you can see, the paste did spread onto parts of the board that we don't want soldering.







Apply some heat (300 deg, airflow about 1/3rd) and - ta-da!





Similarly, to solder the PIC 18F2455 SOIC SMT package neatly, first start by spreading solder paste all over the place:







Put the chip down with it's feet in the gunky stuff







Add the magic ingredient (heat) - and here's the finished job!







We tried to take a video showing the actual process, but fat fingers and moving parts close to the camera made the focus go all fuzzy. Here's a video from YouTube showing the same soldering process (but when heated from below rather than above).

Just like hot air soldering, it's pretty boring. Nothing much happens until about 1m:30 into the video. Then all of a sudden, the magic happens....