It’s been a while – too long in fact, since I took a look at the stats for any of the sites I run. A complete change of emphasis about what is important and what is not has occurred since the ‘jump start’ in Hospital back in the early spring. Now I’m not complaining. I’ve been more settled mood-wise, than for many years, and it continues, with the odd hiccup, but you know what I mean.
The resolutions I made last year, to cut down on current projects, and curb my unstoppable desire for new ones have been abandoned, although quite a few projects have been completed. I try these days to spend more time with the guitar, and finally writing out properly, almost all the songs I like to sing (Songs For Broken Voices – on this site) I can practise these in a timely and organized way.
Today I took a glance at the stats for http://connectable.org.uk, thinking that as now I only update this only occasionally, interest would be down – it’s not. Already this year the site has had over 1.1 million hits, and that’s twice what it had last year at this time. http://joebrown.org.uk has improved also, with almost doubling of hits to nearly 0.5 million.
By far the most popular articles on connectable.org.uk are still the PIC USB designs, whilst on joebrown.org.uk the SFBV mentioned above, and the Stories remain very popular. Glancing at some referrers I notice one or two hard-core porn sites have pingbacks to a few of the stories!!
Talking of stories, my dropping one of my medications has resulted in a much shorter night, and the thought-engine performing as though on amyl nitrite, though I just as fast delete large sections of the story I’m currently working on, as add them, so progress is more variable.
Another mood-enhancer has been the ’summer’ – if I can describe what we get here in Newcastle as summer. But my love affair with light carries on mostly unhindered, apart from the really dull days – yes there have been some.
Now that things seem a little more settled, I’ve even been toying with the idea of finding myself a fun-loving baby-boomer girl again, to cuddle, amuse, entertain, and possibly even love. So watch this space.
Well, er – sometimes very hard.
Producing a circuit board sucessfully, on a one-off basis, using ad-hoc methods and tools is manageable – up to a point. The amateur is faced with all of the variables that are simply factored out in mass-production – temperature, light, chemical strength etc., etc. This is all bad enough for what used to be ‘normal’ size technology – IC’s with pin-spacing at 0.1″ etc., but a whole new set of problems arises when things are scaled down and surface-mount components are to be used.
The easy part is drafting the schematic and drawing the circuit board on your PC. After that, it’s uphill all the way until the last solder joint short-circuit has been cleared, and it’s not hard to see why SMD is regarded by some, as yet another nail in the coffin marked ‘amateur electronics’.
I think this is a shame, so I’m going to indulge in some neck-stretching. No, I’m not an authority on photography, chemistry or any of the other ‘ys’ that are involved these days in PCB production, but I’ll describe my methods, which have met with some moderate success, in a bid to keep interest alive, and encourage those who are put off by SMD to give it a go.
First of all, there are no special tools required for SMD PCB production over and above what you already use successfully for other PCBs, with the possible exception of some serious magnification aids. I will show in this post that these need not be expensive if you are prepared to ‘hack’.
Nor are special boards or chemicals. What is required is a reasonably strict regime in the way that you go about the manufacture, make notes of the detail of your successes, and those of your failures, and hence learn by any mistakes.
Let’s start. You’ve drawn up your board – I’ll use a recent small header board as my example, shown exported from Eagle in the pic below. As an idea to scale, the pin headers are at 0.1 inch pitch.
PIC 18F6620 PCB Top Foil (Printed from Eagle)
I printed this foil pattern (in black) onto best quality (£0.10 per sheet) Laser Transluscent Film. I chose all the high quality graphics settings on my Samsung Laser printer, switched off toner saving and switched on ‘Darken’. I cut a piece of ‘economy’ (paper & fibreglass) FR4 board and exposed the board with the negative for 60 seconds in my light-box. This has 4 X 16watt Sylvania Black Light tubes, and is commercially made.
I developed the exposed board immediately in MEGA Electronics developer, made from SENO 4006 concentrate, mixed according to their instructions in the ratio 9 parts tap water to 1 part concentrate. This develops fast, faster and blazingly fast, depending on temperature, and how many boards you’ve already developed with it, and I’m always careful to under-develop, wash, inspect and re-immerse if necessary, rather than ruin by over-development. So far so good, but let’s stop there and rewind.
While you are fiddling about cutting the board, switch on your etch tank to warm up (if you’ve got one) or warm up your solution of ferric chloride in a teflon-coated pot. Prepare at least 2 jugs of water, and lay out your plastic dishes, one for develop, one for wash. It is also useful to have a bucket for waste water. A good way of seriously upsetting your significant other is doing ANY of this in the kitchen – find a spot that is well protected against the irreparable harm ferric chloride does to almost any surface.
Back to the story. If you are happy with the developed board, wash thoroughly then pop it into the ferric chloride solution. While it bubbles away, replace your wash water, and clear away your developer. Even with a bubble-tank, I find agitating by lifting the basket up and down frequently speeds up the process. When the board looks nearly finished, take it out and wash thoroughly, then inspect with an eyeglass, making sure that you aren’t over-etching. AT NO POINT during this process rub the surface of the board with ANYTHING. If you want to dry the board for inspection DAB it softly with soft paper.
Now, take a look at the pic above. The white perimeter ends up as a photo-resist area on the board. It is an excellent indicator of when things are cooked, or slightly over-cooked, because I etched my board fully, and the perimeter was almost all eaten away. When you are happy, wash well.
Now I had something that looked like the pic below. Note that the photo-resist is still on the board. Note also a short circuit just to the right of the six-pin header on the left-hand side. I corrected an over-generous width on both traces in my Eagle design, and cut the s/c with a sharp scalpel. Despite the odd ’suspicious-looking’ area, there are no other shorts on the board. (I buzzed it) There is a definite break on the 1st trace from the bottom of the board – probably a hair caused this, but it’s not serious. If the break was on one of the traces near the chip, it would be more problematic.
PIC 18F6620 Board after etching
The next photo shows the board after I’d cleaned it with cellulose thinners. I DONT ’scrub’ the board as advised sometimes, as this inevitably leaves minescule bits of copper and photo-resist wedged into the track edges. The bright marks on the board show where I’d started to buzz it for shorts, and the scratches on the left show where I’ve cleared the s/c. I’ve also clipped the board to size and chamfered the corners.
PIC 18F6620 Board Resist removed.
Is that it? Well it could be, but I like to tin my boards, as it greatly eases soldering. I use MEGA Electronics Immerse Tin Powder mixed according to the instructions, with 90gm of powder to 1 litre of hot tap water, ensuring the solution is cooled before dipping the board. The finished, tinned board is shown below – now get it drilled and start soldering!
18F6620 Board - Tinned and ready to solder
BTW All photos were taken with my hand-held Agfa 2030 in macro-mode, with no flash, in daylight next to a window. I reduced these down from 4000px square to roughly 800px in this post.
For those like me who are short of lamp-oil, some aid to visual inspection of the PCB is essential before, during and after soldering.
I use the 8X inspection magnifier pictured, made by Waltex, which will resolve down to less than 1/10 of 1mm. (pretty small) If you like a big picture then hack a half-decent web-cam to bits and mount the business end onto the top of the magnifier as shown. For really serious magnification, I have a similar arrangement mounted on a small cheap microscope.
Waltex X8 Magnifier
Waltex X8 Magnifier with CCD (web-cam)
And Finally…
Yeah – you guessed right. In creating the notes for this post, I deliberately walked through the whole procedure, making the test board as shown. Concentrating on capturing my actions, I forgot to produce a ‘mirror’ from Eagle for the Top (and only) track foil pattern of the board. The result? A board that is the mirror image of what was really wanted. Now this isn’t the 1st time I’ve done this, nor probably the last. In the past I’ve been known to bend back IC pins through 180 degrees and mount the chip upside down. How easy is that with SMD? Well very, actually, but it’s not so good when you have to mount the pin-headers on the ‘wrong’ side of the board. You have been warned!
The following (and last) pic shows the soldered and working wrong-way-round 18F6620 header plugged into my test-motherboard. (to which I’ve added pin header sockets to on the bottom of the board)
Brute-force and ignorance win the day! (Don't do this at home)
Because of my total inability to ‘do nothing’, whilst in the Throne Room, on my way I usually pick up at random, a magazine from my enormous stash of electronics mags from the past. Most of these magazines are now long extinct, and I’ve often mused as to the reason. The truth is there are probably several reasons, not the least being the attempts by Margaret Thatcher at social enginnering, in trying to turn us all into barrow-boy traders, instead of engineers – our real heritage and strength.
Leafing through the content of ‘Practical Electronics’ circa 1990 (I’ve been deliberately vague here to spare the author’s blushes) I came across the following drivel in an article entitled ‘Computers’:
“…blah, blah. To sum up then, machine code is ok for small programs up to 1K for a fixed purpose or where speed is essential, eg a fast computer game. Assemblers are used where timing is critical and an efficient code is required. High level languages are used where there are a lot of unskilled programmers or where a very large program is being written which might require constant or even drastic alterations.”
I’ve reproduced the above verbatim, including the several lexicographical omissions and errors. There are two important facts obvious from the above. The author hasn’t a (expletive deleted) clue what he’s talking about, and the editor of the magazine either dosn’t know either, or simply dosn’t care, or hasn’t actually had oversight of the article.
Sadly, this is only one example of the complete shite that abounds in today’s popular magazines, the further evidence of a dumbed-down, Blue-Peter approach to technology, and worse. That would-be young engineers are buying this rubbish naively expecting it to be both informative and accurate, neither of which is true anymore, is a crying shame.
The only proper destination for this stuff is to cut to size, and hang it on the nail – trouble is, even the paper is of poor quality, and would be far too scratchy for my delicate skin.
This unit provides 4 autonomous MIDI inputs and 1 MIDI output. Note this is a ‘proper’ MIDI Merger – all 4 MIDI inputs can be used at the same time, unlike other ‘designs’. The unit also provides an indication of the channel number being played, and has shown itself to be capable of expansion into a full-blown controller.
The PIC microcontroller I used – 18F4320 was being sold off cheap, at £1.00 each by Crownhill Associates, in Ely – but don’t pester them for any 18F4320’s at this give-away price, as I bought the rest of their stock!
It’s always worthwhile to take a glance at their website, as inevitably they have PICs at discounts you wouldn’t find anywhere else. A purchase I made this week, was 5 PIC18F6620s – a 64-pin TQFP monster PIC – at only £2.00 per pop!
The intention here is to provide details of the schematic and photographs/advice on construction. The PIC code will be discussed more fully on http://picprojects.info.(shortly) All source-code is provided in this post, together with Eagle project files for the printed circuit boards.
The front panel on the prototype - I used 'Front Designer'
The schematic is below. Apart from the PIC and it’s crystal, the other main components are 4 6N138 opto-isolators, 5 on-board DIN sockets, a voltage regulator, and a few resistors. I mounted the LEDs on a separate interface/indicator board, and the schematic for this is shown later. The handful of pin headers are used to add a key matrix and FTDI USB-TTL lead, for upgrading the software, using an internal bootloader.
MIDI Merger/Indicator Schematic using PIC 18F4320
Following are some views of the PCB. Note these are not all to the same scale. The complete Eagle project for the PCB is available for download.
Component size of printed circuit board. (I mounted my LEDs on a separate board)
Printed circuit bottom foil pattern
Midi Merger PCB top showing links (or top foil)
The assembled prototype, together with user-interface.
View of the unit before front panel fitted.
Rear view of unit showing MIDI sockets and DC power socket
As shown in the main schematic, the unit functions as a MIDI-Merger and Indicator. With the addition of a keypad, extensions to this are easily added. I added the following, mainly because I find them useful.
MIDI Minimum volume (set on a channel-by-channel basis)
MIDI Channel re-assign – Re-assign any MIDI Channel to another
Filter-out unwanted MIDI commands – Get rid of those pesky pitch-wheel messages from your MIDI Guitar Unit!
The front panel I have shown above – I created a separate user-interface board that incorporated a 16-key matrix, and duplicated the reset switch and LEDs.
The 4 resistors are 10K in value and the capacitor is 100nF. I used small TACT switches and extra-bright 3mm LED’s. I used 2- double-row pin headers to connect everything to the main board.
MIDI Merger User Interface Board Schematic
MIDI Merger User Interface Board - component side
The MIDI Merger User Interface foil pattern
The MIDI Merger User Interface links (or top foil)
Photo showing match between front panel template and User Interface board.
Construction
I’m going to be bold here and tell you to forget buidling electronics in the way that instructions are given with a self-build electronics kit – you know the ones that start by telling you to stuff the board in the strict order: Diodes, Resistors, Pin Headers, Capacitors, blah blah. You will no doubt have experienced disappointment when the gizmo didn’t work, and there followed a long tedious trail of fault-finding.
My method of constructing Microcontroller projects was borne out of the experience of developing both the schematic and the software, making fault-finding a complete nightmare unless a simple procedure is followed – iterative development, or if you prefer it creep before you walk.
Take a look at the photo below – yeah there ain’t much on the board yet – but we know the PIC is working, because we’ve made an LED light up with it. Take a look at the ‘main’ procedure in any of my software and you will find a simple LED turn-on, just to give me confidence that the oscillator is working – (crystals can be destroyed with excessive heat when you solder them) and my program works.
But even before we get here, you should have buzzed out every pin on the PIC socket to it’s neighbour, looking for shorts, then switched on the unit with only the regulator installed, and tested that you get 5 volts where it should be and nowhere else.
Note too, that I’ve connected up an FTDI USB-TTL cable to the main UART on the PIC. The 1st thing I always program onto my PIC’s is a bootloader, and that will be sufficient for you to test that the PIC is working and load up your ‘real’ software when you are ready.
Add components in a logical sequence – functionality is the key. In the case of this board, adding a MIDI input stages components, buzzing for shorts then live test is the order of the day, before moving on to the next.
Also, if you have the bootloader installed, and the board connected to your development PC, if there are problems, comment-in/out relevant sections of code to ascertain that your hardware is working. The flash memory is good for 10,000 updates – I promise you, you won’t need this many!
Do a little at a time, then test, then another small step, then test -you got it?
Do (only) a little more, then test again.
Until it's nearly complete.
Oh, and there’s just one more thing – always start with a clean and uncluttered work-environment!
Always start with a clean and un-cluttered work environment.
Below, I’ve posted an annotated waveform captured from the Merger whilst it was being developed. The Blue trace was captured with one probe of the ’scope on the collector of the opto-isolator darlington transistor. The red trace was generated by my code and was captured on PortB, bit 7.
BTW The picture is dumped direct from the PicoScope program. I annotated it using the excellent (and free) PhotoImpact 12, from ULEAD.
Also interesting is that the complete Note-On 3-byte sequence has been transmitted and received within 1ms – a credit to the UART on my keyboard (built in 2004 using a PIC16F876A), and the excellent response time of the INT0 edge interrupt on the 18F4320.
Waveform of MIDI sequence 0x92, 0x30, 0x7f and sample points.
At the end of this post, I’ve given the part list for the main schematic generated from the Eagle project. A similar list can be generated for the User Interface board, so I won’t repeat this exercise. All parts, apart from the PIC, but including suitable PCB stock, are available from my favourite (and incredibly handy) electronics stockists ESR. Their prices are reasonable, there is no minimum quantity restrictions and they will deliver anywhere in the world. Their website is here: http://www.esr.co.uk
and I will post and date updates as they happen. Note you will need the C18 Microchip compiler to build the project. The free student version is perfectly adequate for this. The compiled hex file is included for those simply wishing to instal the firmware.
The source-code, with special emphasis on the implementation of the interrupt-driven software UARTs, will be discussed more fully at http://picprojects.info This will be done shortly.
An annotated hi-res Interface schematic is here: http://picprojects.info//MidiMergerInterface_Annotated.PNG showing links to port pins and resistors on the main board.
On this (and in the source-code) you will see that I have interfaced the key matrix as follows:
Columns (inputs)
Bit3
Bit2
Bit1
Bit0
RA5
RA4
RE1
RE0
Rows (outputs)
Bit3
Bit2
Bit1
Bit0
RE2
RC2
RC1
RC0
Which are the 2 pin headers next to the oscillator crystal.
Parts List for MIDI Merger/Indicator main schematic.
Warning. This post contains ranting and incompletely-redacted profanities. Read at your own risk.
Candidate for Prize For The Most Useless Product Of 2010
Astonished I wasn’t. Despite a heavy-weight list of powerful agents contained in it’s formulation (non-ionic surfactants and perfume), this product failed to give satisfactory results in tests on my sink – in fact it was f**cking useless.
However there is mitigation. After several hours of testing on various surfaces to find any at all it would clean, I discovered it’s only just less effective than tepid water at removing green algae from my uPVC window-frames.
So – don’t throw out the vinegar and brown paper just yet.
Warning by WIKI. Some surfactants are known to taste good to animals, ecosystems and humans.
Interesting – I didn’t know ecosystems had taste buds – we live and learn, but best not let your dog lick the window-frames.
This article contains material that some readers may find offensive and/or challenging. If you are easily offended, then please do not read on.
By the very nature of this article I have to respect the feelings of those I have known, and those that know me, so this is by no means a full-on confessional. Let’s just say that when I hear others around me criticising others behaviour, especially that of older kids, I consider my own errant behaviour in the past, and keep my gob shut.
I’ve been a risk-taker, probably for the largest part of the life I can remember. I never thought about this until very recently, when I’ve had time to reflect on some of the (frankly mad) things I have done. That is me, that is who and what I am.
Hopefully you are different. Not different enough to make me defensive, or worse, agressive about you, but different enough for me to be interested in who you are, what you are and (maybe if you’d tolerate my impertinent questions) why you are as you are.
Recently I’ve been writing a few short stories and using re-captured old memories to inform some of the narrative of these stories. The reasons why the other principle characters behaved in the way that they did fascinates me now, in a way I didn’t give a second thought to, at the time that the events took place.
It didn’t seem strange at the time, but I was allowed the freedom to go camping far away from home, sometimes for 4 days or more, at the age of 12. This was incongruously coupled with constant warnings about ’strangers’, and the indescribable acts against my person that might be committed by them, if I didn’t get home by 10.00 pm whilst I was at home! Parents today would never rule in so random a fashion, and yet I don’t believe that the threat to our kids is any more (or less) than it was then. Sadly, it is now accepted that kids are more at risk from the people they know, (and trust) rather than strangers.
Incest wasn’t talked about in polite company – especially by parents to us children, but I was aware of several families, the behaviour of which was almost blatant, and nothing was ever done about it. Like the alleged practises of families of Bonobo monkeys, casual sex between the members of an incestuous family is said to pass for love and affection. Rejection of the advance such a family member may make to an outsider, may result in the the family member feeling that the person ‘dosn’t like them’.
My experience at first hand with a young female from one such family was one of mutual incomprehension. I couldn’t understand why she had sex with almost every young lad that wanted it with her, and she couldn’t understand why I didn’t want to have sex with her. She expressed hurt when I rejected her overtures, telling me she ‘liked me a lot’ and asking ‘why don’t you like me?’. I had told her that I did like her, but wasn’t ready to have sex with her. The great sadness here was that I believe she ‘liked’ me in the accepted sense, i.e. especially, but had found no other way to express her affection other that offering sex, so it was difficult for me to understand that she regarded me in any way differently than all the other boys she had bedded. The truth is I did want her, she was extremely feral, both in behaviour and in appearance, and as a result, I was fiercely attracted – but sadly also repulsed by her serial promiscuity.
Another factor which I found attractive, and eagerly explored, was incongruity. Whilst still quite young, I dated a young lady, who not only was several years older than me, she was also several inches higher than me in height! Truth was, I just about worshipped her. She had natural golden-blonde hair and was absolutely stunning – stunning enough to be May Queen one year, in the town I lived in – and no, I’m not making this up. What turned me on most was that she was taller than me. I haven’t been able to explore much further with this particular aspect of attraction, as having attained full-height, a few years later, I’ve been 6ft ever since, and I haven’t had the privilege of re-testing my tall-female disposition any further, well not in England anyway. Mind you, there was a Dutch lady while I was in Spain…
High in my incongruity stakes, were the ‘oddness’ (as I thought) of what a particular girl did. There was a pretty young girl at a party, and as we sat talking on a settee, she told me that she worked in a local sausage factory. That was enough. I had made some quip about her handling sausages, and then kissed her, mostly to stop myself from insulting her by laughing out loud. We went out together for quite some time afterwards. (until her mother started talking about marriage)
There’s also something about sisters. Being ‘in-between’ – an unhappy place most of the time – my older and younger sisters, I found my strong attraction to girls who were sisters difficult to understand, but when presented with strong affection by both from a particular family, (no, thankfully not at the same time) found no difficulty at all (moral or otherwise) in reciprocating. I loved them both, and they still have a place in my heart.
A demonstration of spirited defiance by a female also guarantees my instant interest, although this is probably not so strange, because I prefer people who have strong opinions, and the passion to express them. Wishy-washy compliance I find distinctly unattractive – especially as it is usually accompanied by ’silent’ protest and secret scheming (passive-aggressive behaviour?). A long while ago, a full-blown row about noise with a neighbouring young woman in the flats I once lived in, turned into a passionate and mutually satisfying affair.
Then there’s being ‘the other man’. Knowing that a girl is already courting was as a red rag to a bull. Mind you, such enterprises shouldn’t be undertaken unless you have a strong belief in yourself – as doubt and uncertainty are an integral part of the game. The prize was always worth it when she finally dumped him – losing always chalked down to ‘experience’, so ‘defeat’ didn’t enter into it.
The biggest turn-on of all is danger. Turning up for (a free) breakfast as a guest at the Tarn End Hotel (Brampton) having spent the night in the owner’s hay loft proved to be an almighty high – and the lies I told him to explain the lack of a car, were just lime pickle on the curry. Having beautiful clothes helps, and I recall my somewhat dandified appearance in a beautiful Royal Blue velveted-cord jacket and herring-bone tweed trousers – my scruffy motorbike clothes were still up in his hay loft.
I was criticised as ‘wild’ by some, no, by many – it’s just as well that they didn’t know how ‘wild’ I was, or wilful in the face of their criticism. As I grew up, I found I had fewer and fewer playmates. Earlier on, this was mainly because parents of putative friends forbade their offspring to associate with me. Later, because the friends themselves found my actions and behaviour either unacceptable or downright dangerous.
I’ve been described as the personification of many different evil geniuses from the fairly mild ‘Dennis The Menace’ to the rather praiseworthy ‘Spawn of The Devil’. Ma Elrick, my 5th form tutor at school said she couldn’t make her mind up about me – whether I was a grossly-misunderstood genius or a perfect fool!
Perversely, I understood exactly what she meant, as I couldn’t understand many of my actions either. This was after I’d convinced our headmaster Mr. Brace, that it was better that I smoke in the locked formroom at lunchtime, rather than set a bad example by doing so in the boys bogs, or standing outside the school gates!
The testimonials still ring loudly in my ear. Our English teacher ‘Taffy’ (yes, he was Welsh) said when I visited him before he retired. “Ah, Mr. Brown, I will remember you – and not just for all the bad things!” I loved him for that, and that he had taught me to read the ‘dots’ – something I shall be eternally grateful to him for. His crushing disappointment when I had to pull out of the soprano lead at our concert in Gateshead Town Hall, because my voice broke, was palpable – but I digress. His experience of me had been a roller-coaster ride of admiration (at my grasp and love of literature) to downright despair – when I insisted in perpetuating my Cold War with Mr. Banns, our French teacher for four long years. He had tried to reason with me that my treatment of the teacher would only do me harm – he didn’t realise that I was ready to face self-destruction rather than accept that Mr. Bann’s behaviour had been reasonable.
But, as Jim Golightly once said “Who the fuck’s Papert?”
I’m pleased to report that I’ve successfully implemented 16-bit SPI communication between my Chordar project controller, a PIC18F4620, and the VLSI VS1103b MIDI Synth chip on the Sparkfun VS1103 BOB.
The hardware for this is as shown in the previous post. The source-code, and a short discussion of it, can be found on my picproject.info site at: 16-bit Software SPI Implementation on PIC (PIC18F4620)
These pages (and those at http://picprojects.info) will be updated as development progresses.
No it isn’t a mistake, it’s the breakout-board I would like to have seen made available off the shelf from Sparkfun. Those familiar with these pages will note that I documented how to connect up the VS1103 BOB from Sparkfun on a breadboard a few weeks ago. (Ultra-simple MIDI Synth using VS1103b Sparkfun BOB)
Since then, I did further work controlling it from a PIC 18F4620 using software-implemented 16-bit SPI. The lashup got to be very messy, so I thought I’d take some time out to do the job properly, and make a PCB for the implementation. As the PIC I’m using is already installed on another PCB, this card implements the MIDI and SPI interfaces only. Those wishing to use the MIDI synth stand-alone, can simply leave out those parts of the SPI interface not required.
I’ll start with some pics of the finished board being tested, followed by the schematic and layout of the PCB.
The assembled board, less the 6N138 opto-coupler and the sparkfun BOB.
Another view of the assembled board.
The sparkfun Vs1103 BOB BOB early testing
Another view of the BOB being tested.
Note in the above picture that I’ve not left sufficient space for the pin-header located near the MIDI socket, and consequently the spakfun board overhangs it. The plug will fit, but it’s tight. I’ll move it out a little in the 2nd version of the board.
Top view of VS1103 BOB BOB
Sorry about the flash burn-out on the last two pics. That’s because winter has descended once again in Cullercoats, and the sky is as dull as dirty dishwater.
Now for the schematic and PCB layouts. Nothing startling here. I’ve used resistors to step-down the 5v TTL levels from the PIC, and outputs from the VS1103 are fed directly to inputs on the PIC, as they are sufficiently high to be reliably read by the PIC. 3-pin link headers are used to select default MIDI and/or PIC control. The VS1103 RX pin is also switchable, so it can connect directly to the PIC if required.
The VS1103 BOB BOB Schematic - a complete MIDI Synth
As the project continues the PIC source-code will be documented and discussed on http://picprojects.info. Any information and news will be posted on this site.
I needed a stand-in for the now non-operational headphone amp on the Alesis Mixer I recently ‘resurrected’. An op-amp and two discrete transistors came to mind, but I dismissed this for my solution. The TDA2030A has been around a long time, but is still readily available, and more importantly, is only pennies more than an op-amp in price.
The schematic I present below is lifted unashamedly from the TDA2030A datasheet. There is also a PCB design in the Application Notes for the device, but I preferred to roll my own, paying cautious attention to the layout of the PCB – the GND runs in particular. With the components given, the amp output is clean and shows no signs of instability. I did all my testing on a 15-0-15 volt power-supply. Note I’ve included two 10 ohm resistors for two sets of headphones, and I’ve also brought out the amp output to a pin-header so that the amp can be used as a power-amp also.
The Eagle Schematic and PCB files are here: http://joebrown.org.uk/images/Headphone Amp/Headphone Amp.zip
The fully-working amplifier, including hand-made heatsink.
Note that if only heaphones are to be connected, then a much smaller heatsink will suffice. I used the amp without any heatsink at all, and it made no complaints.
The completed amp, before fitting the heatsink.
The PCB, after etching.
The TDA2030A Headphone Amp Schematic
The TDA2030A Headphone Amp PCB Foil Pattern
All parts are available from my handy local stockist ESR.
