Back a few years ago, I ventured into making my first PCB in over 2 decades. it was motherboard to hold a raspberry pi zero, and fit within a zx spectrum case.
it was inspired a little by an article in MAGPI magazine by a Mr P J evans.
I did kind of goof it up a bit, so relegated that to the ‘ideas to do in the future’ drawer
With a successful 2nd Kickstarter – The Spectrum Next will have between 8,000 and 9,000 users.
Lets Dream a little and imagine a Bright world where all the users have a Super LED Blinkenator 2000 installed….
9000 users = nearly 40,000 inserts to be made!.
lets say just 10% want the blinkenator, I still have to make nearly 1000 of the things.
I’ve been researching a little and identifying bottlenecks to SUCCESSFULLY produce and deliver my board in those quantities
There’s some scary numbers!
So, I’m now pressing forward with TWO designs. one design, the one you’re all familiar with, suitable for small time production in small batches here and there on my weekends, only ever endeavouring to sell maybe a 150 units ever
and the second, a ‘mass produced’ item that requires minimal ‘hands on’ time from me to deliver, but will require some significant outlay up front.
The pictures above are a first run result of my Design For Manufacture for the inserts….A different injection mould, possibly 2 parts, maybe 1 and using a flexible PCB!
some key notes……..
Advantage – no connector soldering needed on my part – currently I’m soldering 16 cheap ‘bridges’ to each main board. with this insert, someone will be soldering 8 SMT FPC style connectors
Advantage – it’s likely that this design will be easier to make ‘injection moulding’ manufacturable. the existing design is tricky, but not impossible
Advantage – FPC connectors are a bit more reliable and easier to use than my bridges for the end user
Advantage – FPC / flexible PCB ‘legs’ on the inserts will mean a little bit easier installation by the end user
Advantage – Uniformity of Light – This type of construction allows for a much thicker ‘top layer’ – which will diffuse the light far more. Also, more of the insert will be better lit up ‘from below’ rather than from the side that i’m currently doing.
Disadvantage – FPC connectors are more expensive
Disadvantage – Flexible PCB’s are more fragile
Disadvantage – Flexible PCB’s are more expensive than FR4 for small quantities, so prototyping ability is very limited. at The quantities I need though, there’s not that much difference
There’s more i’m sure, once the final numbers are ready, I can see if a kickstarter makes sense, it may not be financially viable if the whole thing needs to be sold at £80 each……
if I can get closer to that £50 mark, then who knows!
to use some PCB grounding spring contacts to provide a quick fit connection didn’t really pan out – the contacts simply didn’t solder on easily, too difficult to align correctly and quite weak – I tore a few pads off trying to get them aligned and correctly ‘grippy’ on the insert.
multiply that by 16 each board – the first one took me about 2 hours to get to be in an ‘ok’ state – Not really acceptable for a mass production product – not that this’ll be mass production but I’d rather not spend half a day on each of these getting them ready for sale……..
The second slight issue – See the photo below
The PCB is laid out on top the next board in the position it’ll be installed in.
There’s a prize for someone that spots the goof-up
Have a further look at the PCB powered up………..
First Light! – The board works 🙂
Yeah, I got the inserts ‘back to front’ – That’s the result of working on a bottom mount PCB from the bottom…….
There’s two ways I can fix this
Simply rotate each LED by 180 degrees on the PCB and install a bodge wire to swap the input and outputs around………
OR….
I can simply re-design the LED insert and improve upon it!
a few reasons to re-design,
The first 6 LED version still has a bit of point brightness – I fear that even with the SLA printed inserts it won’t be diffuse enough..
Some statistics
8 LED’s – This should spread out the light more, reducing the hotspots a bit
0.4mm Slimmer – this lowers the LED’s further into the case, allowing much more plastic to sit above. I’m hoping this will de-focus the light more
Reversed connections to match the reversed controller board!. reversed is the new non-reversed now 🙂
New insert PCB’s are on order and should be here in a couple of weeks, I’ve bitten the bullet and ordered FIFTY….Also a few hundred more LED’s and a large tube of solderpaste.
Doing these first 10 dev boards is going to be fun – 320 1.5mm LED’s to be hand soldered!
The Controller board fits inside the case almost perfectly
I’ve slightly offset the J15 connector on my PCB to the one on the next. This offset gives a lot of friction, but needs some long term testing – the standard header I installed on one of my boards seems to work well as a friction fit. BUT, i’m not convinced that 32 LED’s, each pulling 5-20mA, (depending on which datasheet I refer to) – or between 160-800mA total depending on how I end up setting the brightness…..800mA is a LOT to pull
I’ve purchased a new gadget – A Riden RD6006 Benchtop ‘power supply’ so once i’m set up, i’ll charaterise the LED’s and current draw to set the software limits appropriatley
I doubt i’ll take nearly an amp on this board 😛
One further small mistake on the dev board –
That 3V3VCC – it should say just VCC
When originally designing this controller board, I was to use a 3.3v Arduino to make it compatible with the Next’s 3v3 i2c.
For a few reasons, I’ve changed to using a 5V arduino and putting on-board a level translator device – this gives a 5V buffered i2c output that anyone can easily plug into
I forgot to change the net names….The board still ‘thinks’ the Arduino is either powered from RAW (it’s ‘unregulated input’) or 3V3 VCC…
The RAW input drops a few volts through a voltage regulator on the arduino to give the arduino a nice regulated 5V.
The next output is 5V….it’s not enough to power the Arduino through the RAW pin…
Took me quite a while – and a bit of soldering hackery to figure that one out as the speccy picked the board up perfectly when patch wired in place..
USB powered, it works perfectly
in the Next it doesnt….
The fix – I think I can just short the RAW pin to the unconnected VCC pin on this first batch –
and, finally
See that i2c device, found at address 0x45………..That’s the Blinkenlight 2000 PCB :-), alive and inside the Next!!!
