QL prototyping board...

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Dave
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QL prototyping board...

Post by Dave »

I've used my last prototyping board today. It's time to order some more. Since I can reduce costs by increasing the size of my order, I thought I'd share my basic design I've been using since 2013, based loosely on the design we used at Sandy.
Don't call her fat.
Don't call her fat.
What you're looking at:

The top left takes a 7805, and if you need it any DPAK 3v3 or 1v8 regulator you like. They are well outside the QL case. The copper fill acts as a heatsink. Both regulators have provision for ceramic or electrolytic caps both before and after and polarity is indicated. Power distribution is done as on solderless breadboards. The power tracks are on both sides of the PCB, and the hole size in them is slightly reduced to increase conductor area. I ran a separate power bus from the 3v3 regulator alongside the SMD pad area.

On the left is a general output area for .1" headers paired with a wiring area totaling 28x2. There are two rows of that. Also great for jumpers. Then you have four areas of 25 rows. Three of those also have a 20 pin SMD pad for ICs I often used, broken out for easy access. That's just what I was using back then. The left two areas sit well outside a QL, so you can continue onto regular breadboards or other bulk PCBs if you wish. This board is 186mm x 100mm, .062 and 1oz, FR4.

After a brief safety area (I killed some QL components with an accidental short to the connector - lesson learned) there's the J1 connector, then a copy of it where you can either just put in 2x32 strips, pins or a DIN connector facing up - whatever suits you. Both connectors are clearly labels for pin position and row A or B as that trips people up a LOT.

I used the silkscreen layer to create an area for labeling the board with sharpie - you can erase it with solvent that won't touch the silk or resist layers ;) One smart evolution was putting a write-on area by the DPAK so I could label the voltage clearly on the extra power track. There's a big difference between 3v3 and 1v8 - just ask any component!

Anyway, I need to order a dozen more boards to get me through the next few years and I thought these might be useful to experimenters out there. I plan to make some changes anyway but if anyone is interested in using some I can fine tune the board for their general needs, as long as it's still useful to me. Basically, the more boards I order the cheaper they are. I can't support a lot of different SMD footprints, so I just buy cheap footprint to DIL boards from china for 20c each and use those. If anyone has strong opinions of what I should do there, let me know.

The white vertical lines do not separate the areas - the power bar does. The lines are just a visual cue of where to put the DIP packages ;) If you cut a 5-bar in the middle, you can get most .2" and .3" DIPs double stacked within each area to increase density. The groups of 5 holes are only joined by tracks on top. My earlier batches they were joined on both sides, but I realised it was hard to cut tracks correctly on both sides, and also sometimes it's trickier to do when all the pads are soldered. Just linking them on top and forcing any cuts to be there also makes them much more visual, which is better for tracking your circuit. I've had a couple of via shorts from not aligning cuts correctly -- "cut 2" can change direction when you flip the board, and the middle thru-hole acts as a via rejoining the tracks, which doesn't happen with this single-bar design

Where these really come into their own, besides prototyping, is when you want to make a veroboard or solderless breadboard design more permanent without the hassle of making a whole PCB. It's sturdy and suitable for shipping prototypes to others for testing, where solderless board just fall apart!

Changes I will make this weekend include:
  • Add a fuse area
    Reverse the 7805 to reduce thermal load on the adjacent regulator, increase copper fill/heat-spreader
    Adding a version box, maybe a date box?
    Move the writing area to the bottom edge of the board and my production ID to the top - writing at the top over all the components isn't as practical as you'd think ;)
    Extending the work area down and up a row each to add two more rows
    Add access to ground points left of the connector area, to improve signal quality and reduce noise.
    Changes requested by interested people that don't conflict with my needs ;)
    I can't support a lot of different SMD footprints, so I just buy cheap footprint to DIL boards from China for 20c each and use those. If anyone has strong opinions of what I should do there, let me know.
So, if you want to have any of these, just show some interest. When I have an idea of how many I need to order I can give a cost to mail them. To save you money, I'd ship them unpopulated because anyone who would want to use these knows what components they basically need for what they're doing. That way they can go in a simple padded envelope by first class mail, for $7.50 or less instead of $13.50 or more! It took me 3 or 4 years to use the dozen or so that I ordered.

If I order 25 they would be around £10 each, if I order 50 that would drop to around £7.50. That's not just the cost of the PCB, but of paying for it to be tested, and shipped - PCBs are heavy. I'd charge a flat fee for shipping up to the cut-off weight where it becomes a package. I'll basically be selling these at cost price.

If you want them with power and connector assembled, hit me up and we'll figure something out, but expect postage to be higher as it would have to be boxed... :P

Please post interest in this thread - it's not a commitment! :D


martyn_hill
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Re: QL prototyping board...

Post by martyn_hill »

Hi Dave!

I would be very interested in 1 or 2 of these prototype boards - preferably with a DIN connector pre-soldered (its a chore!).

I don't suppose you also have any design that still fits entirely inside the QL case?

Regards,
Martyn.


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Dave
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Re: QL prototyping board...

Post by Dave »

I had a design before that fit entirely under the left edge of the case but came out of the slot about 1cm. It was too small for my practical use.

However, if you can find demand for 25 of them, I can do them. I could just design the PCB for you, send you the gerber files, then you could order the PCBs yourself from somewhere less economically inconvenient.


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Dave
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Re: QL prototyping board...

Post by Dave »

So here is a summary of the feedback/requests I've had.
  • • It would be nice if the SMD pads went away and were just more work area.
    • It would be nice if there was provision for a GAL address decoder pre-wired to the appropriate address lines, with a given logical address and couple of chip select outputs...
    • A couple of people asked for the card to be longer. A couple asked for shorter!
I'll work in the changes this weekend and post an updated pic and we'll see if we're closer to something everyone can use!


Derek_Stewart
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Re: QL prototyping board...

Post by Derek_Stewart »

Hi Dave,

This probably an impossible request. How an i terface to connect a Raspberry PI as a Co-processor.


Regards,

Derek
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Dave
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Re: QL prototyping board...

Post by Dave »

There's are a couple of ways to do it. It depends if you just want to pass a. Yet back and forth or if you want to address a block of memory. It would need some hefty GPIO on the pi's side.

I'll email you in a bit and we can talk more about it.


Paul
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Re: QL prototyping board...

Post by Paul »

Dave wrote:There's are a couple of ways to do it. It depends if you just want to pass a. Yet back and forth or if you want to address a block of memory. It would need some hefty GPIO on the pi's side.

I'll email you in a bit and we can talk more about it.
I'm interested in these discussions as well.
Please use a new thread or include me in the email receipt list.
Kind regards Paul


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Dave
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Re: QL prototyping board...

Post by Dave »

I did PM but a thread is better and the discussion is open to all as it should be. I'm posting from a tablet so if you start the thread I'd be grateful. This thing creates typos.


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Re: QL prototyping board...

Post by Dave »

I'm wrapping up development of the prototyping board. It's ready! It has a dual power regulator - 5V @1A and your choice of 1.5, 1.8, 2.5, 2.85, 3.3 or 5v for the second rail.

It will be available in a few weeks when the PCBs arrive. A bare PCB will be £10, shipped. One that has the power supply components mounted will be £14. You will need to supply parts for your projects and a DIN connector, but that and a bit of soldering makes for a wonderful weekend! Another great thing is it can make expansions available where the demand is just too low to justify producing them. It's hard to share a solderless breadboard with a friend, but a soldered breadboard, no problems.

What I would like to do is release a free e-book with plans for at least 10 or 12 interfaces that people can build onto it. Each plan would be presented as a recipe.

Overview
Bill of Materials (ingredients)
Circuit description
Schematic
Assembly guide on the prototyping board (with sectional testing)
Links to code/software, EPROM images, GAL JEDECs etc.

I can already include a 512K RAM expansion, QubIDE, floppy interface, parallel interface, QIMI interface... An EPROM programmer in another thread would be an interesting addition.

The e-book will be free and will not require a PCB purchase. All the designs could also be done on solderless breadboards.

If you have an expansion you think can be built this way by a hobbyist, let me know and I'll include it and give full credit.


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