The BIG Arduino MIDI controller thread

[Mudo]

Although, for anything more than just an arduino and some buttons, you'll probably end up doing some soldering no matter what.

The Dub funny side of things...

[ReggieUK]

I got my leonardo and teensy 2.0 boards this week, I currently have the leonardo hooked up to a 3" trackball with about 8 lines of code (using a couple of libraries).

The leonardo was about £11, the teensy's worked out about £15 each but as they've both got the same chips on them, I can batter the leonardo and keep the teensy boards for 'best' when I've finalised things :-)

I've also got my midifighter built up on a breadboard atm, everything seems to be working so next up is deciding on a case size and what to do about expansion ports, on the midi fighter classic firmware, there is the mcp3004 chip that gives us 4 analog inputs and there is also further expansion available if you add a 4051 multiplexer. At the moment I've got an adxl330 accelerometer hooked up to the mcp3004 but it needs some work on what to actually do with the numbers that it's getting.

Next up is to see whether I can compile the midifighter classic firmware for atmega32u4, shouldn't be too much of an issue.

[Mudo]

Good news to hear, Do you have blog or some documentarion outside this forum?

[ReggieUK]

Not yet, I will post some stuff about it all but I'd prefer to have more stuff to post before I do :-) At the moment I'm still at the stage where I'm deciding entirely what to do about the pcb, it's all on breakout boards on breadboard atm. There are a few ways to go about it, all have their pros and cons, but I'll know more when some breakouts that I've ordered have arrived.

[ReggieUK]

I'll do some quick documentation of what I'm up to here but eventually I'll do something much better. Over the weekend I made a simple mdf box, 19mm thick and big enough to house at least 2 midifighters + space for extra knobs, buttons and faders for the expansion port. I may or may not actually put 2 in there but as the mdf was just scrap, I thought why not :-D In the picture below you can see the top of the box where I've attacked it with a 24mm holesaw, the first couple of holes were a bit out but for my first time cutting loads of holes with a holesaw, it all looked pretty reasonable in the end.

Onto the breadboard, I've labelled all of the major circuits so you can see how simple it is to lay it all out. You've also probably noticed all of the little green 'breakout' boards, the atmega 32u2 and the accelerometer board were pre-built but the 2 in the corner I had to solder the chips on myself, for anyone that doesn't know, it allows me to use surface mount chips on 0.1" 'through hole' PCBs and breadboards. They're also fairly cheap, usually $1-2 a piece, so you don't necessarily need to be able to etch very small pads to use surface mount components in your designs. fyi. the mcp3004 is narrow SOIC-16, 1.27mm pin pitch, the tlc5928 led driver is tssop-24, 0.65mm pin pitch.

The accelerometer was something I added for giggles, I hooked an axis to the mcp3004 analog input chip and as the accelerometer is analog I get a response from it, unfortunately it needs some attention to turn it into something usable but I'm sure it won't take too much code to make it work :-)

I've decided that I'm going to do the first version on separate PCBs, I've designed the PCB for the button inputs, the 74hc165 chips I got were through hole, so they're easy to do, the other chips on the board are simple enough apart from being very small, not necessarily the easiest things to make PCBs for by hand, so as I want to be able to share this project with anyone that can handle a soldering iron, I think the other PCBs will use breakout boards plugged into them. I will probably do smt versions as well but I want to focus on making it easy to start off with.



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[Mudo]

Cool! (And sorry for the delay...)

Keep update us mate, asaic I will do my own.. Meanwhile for all of you who love arduino..

http://www.indiegogo.com/projects/ar...tions-the-book

[ReggieUK]

I've now got the 2nd board design done, DRC checks passed, so that's the leds and buttons, for a simple midifighter classic, that + an atmega32u2 board are all you actually need. I'll get some test boards etched and then we can see whether I release the magic smoke or not.

[ReggieUK]

I've now done a handful of boards, it's getting a bit hectic though. Whilst I'm doing this, I'm also exploring different techniques, to make my life easier but also not trying to get away from my original plan which was to make a midi fighter as simple as possible for others to follow if they want to make their own.

[ReggieUK]

It's been a little while since I posted anything but things are marching on, I started off with everything on breakouts and designed PCBs for those breakouts to plug into, I've now designed some boards to build the modules directly, whilst I've been doing that I've been exploring techniques for soldering (by hand, hot-air, solder paste), etching, tinning and next week, SOLDER MASK, zomg!!!!

I must stress at this point that the chemicals used in making PCBs can be seriously bad for your health if you don't handle them correctly, I used safety glasses, protective gloves and face mask while doing all of this.

Yesterday I etched a design for the smallest pitch chip that goes to make a midifighter, it was a tssop-24 tlc5928 for the leds, my first time and it was a success and means I can hand etch traces down to at least 0.012 of an inch :-)

It's all gone quite well so far, some things haven't gone quite as well as I'd hoped but there haven't been any show stoppers, with a little bit of luck I should have quite professional looking boards out of it.

The biggest success has been the 'dexrin' coated paper (£9.99 for 100 sheets), it's a shiny waxy looking paper that you use in a laser printer, you simply print your inverted PCB design onto a sheet, place the print side down onto the copper side of your pcb, then using a clothes iron you give it some heat for about 1 minute, making sure to go over the whole of the printed area with the tip/edge of the iron. The heating transfers the printer toner from the paper to the PCB and shouldn't leave any of the print on the paper, once that's done, you inspect the board for any bit's that might not have stuck properly and using a black sharpie, fill in anywhere you can see copper exposed that shouldn't be.

Once that's done, the board is ready for etching, this is a fairly simple process, on average a couple of boards will take around 5-10minutes using room temperature ferric chloride solution and the 'sponge method', this is by far and away the best way to etch by hand, the sponge method gives you an incredible amount of control over how aggressive the ferric chloride is with your pcb, it also uses very little etchant, a tablespoon or 2 is more than enough. Here is an image of the 2 PCBs for the midi fighter expansion port, each board is 42mm x 21mm.



Those boards are nice and clean but before they reach that stage, you have to clean the printer toner from the boards, this is quite a messy procedure, I used nail varnish remover as it's cheap and paper towels, once that's done, you can give them a rinse in clean isopropyl alcohol, it can't be stressed enough to use clean isoprop and a clean brush to apply it, if you have to rinse it further, use deionized water only, tap water and distilled water contain far too many minerals which will just be deposited on your board, trust me, you will scream when your copper traces start to go green in a few days :-D De-ionised water is great as all of the impurities have been removed, warm de-ionised water is even better as it encourages the cleaning process and reduces surface tension of the water allowing it to flow under components a lot easier, it also aids by reducing drying times.

At this point, I usually start to solder my components to the board, however, as I've previously mentioned, I've been experimenting with things, one of the biggest issues is getting solder to the right places, especially with surface mount parts, another issue is that copper oxidises over time, eventually, it can destroy the traces on your board, so it's generally considered a good idea to 'tin' your pcbs.

My previous method was to cover the board in flux and paint solder onto it with the tip of my iron but it looks really messy as it doesn't give an even coverage and it's boring as hell to do, the uneven coverage makes it difficult to place surface mount parts. So to combat the ghetto look of my PCBs, one of my experiments has been to try tinning salts to bathe the PCBs in.

The salts come in 2 packets, mix packet A with 500ml of de-ionised water, stir it for a bit, then add the contents of packet B and stir a few times, wait a few minutes and you're ready to rock and roll.

With the solution prepared, put some in a tub and then put your PCBs in the tub, you should see the pcb start to turn grey almost immediately, this is the tin molecules attaching to the copper on your PCB, leave them in the solution for 5 minutes, after which time you should have a 1 micron thick layer of tin on your board which now look distinctly more professional. Not only does it look slick but you get a nice clean even coating ready for soldering.

From here there are 2 ways to go, you can either use a soldering iron and drag solder the surface mount chips onto the board, or you can use a 'reflow' method, either in an oven (not the one in your kitchen!!), or a skillet (again, not to be used for cooking) or a hot air station. If you use the reflow method then you'll need solder paste, you can buy the paste in tubs or syringes, the syringes contain a more viscose mix of solder paste + flux which allows you to use them with a needle to finely control the flow of solder from the syringe onto your pcb. You can also buy paste dispensers, they have to be connected to an air compressor, they also use solder filled syringes but they precisely control the amount of paste that is dispensed, you either click a button on the dispenser 'wand' or use a foot switch, they look incredibly useful and are extremely quick, probably not the sort of thing you'd buy just for a couple of boards but if you make pcbs all the time they can save an awful lot of time.

You can also use solder paste from a tub and apply it with a toothpick, this is a tedious way of doing it, when I originally tried my paste was a bit sticky, consequently it was difficult to handle and ultimately I got solder bridges underneath some leds I was practising on, to remedy this I mixed a little bit of the paste with some flux, this makes the paste a lot thinner and easier to put on the board.

There's one other method that's used, stencils, I haven't tried this yet as it's relatively expensive, especially just for a couple of boards but it will give the best results, just lay your stencil over the top of the pcb, get some solder paste on a squeegy and wipe it across your board, you will get an even layer of solder exactly where you want it.


I've got one more experiment to try, solder mask, this is the shiny coating that you can see on PCBs, I bought 10cc of uv curable solder mask from ebay, you spread a thin layer across the copper side of your PCB, then you print out an image of just the places on the board that you will eventually solder onto a sheet of OHP (overhead projector sheets), you then lay this on your pcb (aligning the print with the pcb), once that's done you put the PCB under UV for an amount of time which cures the solder mask and makes it stick to the board, the print on the OHP stops the solder mask underneath it from being exposed to the UV light, which means I can clean it off, leaving me with a nice coating everywhere except the pads, ready for soldering.

[ReggieUK]

In my last post I mentioned solder mask, I tried it out a couple of times over the weekend, it's a bit fiddly but for 2 attempts I'm happy with the results and confident I can get more consistent results with a few tweaks. The curable solder mask goes off insanely quickly under a cheap uv nail dryer lamp, my first attempt I left the board in for 60 seconds for the initial exposure, which was way too long, the board came out completely solid, so 2nd attempt I put it in for 30 seconds, this time I had much better results:



The board on the bottom right is my 2nd attempt, there are a handful of tiny air bubbles in the solder mask and my alignment was slightly off by < 0.5mm but the pads cleaned up nicely leaving the rest of the solder mask intact on the board. The board I used was a failed etch, so it wasn't a problem that it didn't work 100%, just above it you can see the same board with a successful etch, that's the circuit for the tlc5928 led driver board in a midifighter.

The top middle is 4 boards out of a batch of 12 rgb addressable led breakouts that have been chemically tinned, you can see 6 of them in action in the glowing tube (rolled up piece of paper) behind the boards, they look like the kind of thing you'd use for the lights on a spectra/3d.

Below that is the carrier board for my atmega32u2 board that I'll use for the midi fighter I'm building, also chemically tinned.

The board on the left is a breakout for the mcp3004 chip which is essentially the expansion port circuit on the midi fighter, that was hand tinned with solder and looks a bit cruddy because I didn't get even coverage.