POC COMPUTER VERSION TWO: A New Direction

[plasmo]

I'm a hardware guy all my professional career, hardware guys are notorious penny pinchers; In retrocomputer we have had plenty examples of convoluted hardware design to squeeze out a few pennies. This is because the managers always squeeze the small hardware team and then let the large software team ran up the schedule and money. Having said that, penny pinching is complicated even in retirement when I'm my own manager; it turns out shipping from China is a big part of the pc board expense. So I was just looking at my 2020 pc board expenditure to Seeed Studio ($59 pc board + $84 shipping), and JLCPCB ($197 pc board + $268 shipping), 17 shipments in 2020. Shipping dominated the total board cost. To amortize shipping cost, each shipment contains 3 to 5 designs. Most designs took 2-3 iterations to reach maturity, so a shipment is a mixture of final design iteration, reorder of existing designs, exploratory designs and sometimes last-minute hare-brained designs destined to be cut and jumpered; it is a juggling act and mistakes do happen. I have to remind myself periodically that my remaining time on this earth is far more precious than the little money saved but optimization is a compulsion beating into me over 35 years of hardware career.
Bill

[BigDumbDinosaur]

GARTHWILSON wrote:

Depending on the errors, a lot of parts could be damaged, too.

Even if no parts are damaged due to circuit errors, they have to be stripped from the bad board to be reused. That operation could do damage to otherwise salvageable parts.

[gfoot]

BigDumbDinosaur wrote:

Quote:

Beautifully fabricated, I don't know how they can build it at $1.60 per board.

I too wonder how they do it. I recall in the not-too-distant past when getting a prototype PCB made cost at least $500. These days, $500 can get you a whole pile of boards if you choose the right board house and your design isn't too big. I'm guessing the charges for hobby-quantity orders are little more than a break-even price that is readily absorbed by the orders for production quantities that are JLCPCB's bead and butter. The shipping charge for the POC V2.0 board with a template is nearly as much as what I'm being charged for the parts themselves.

I think it's just that they have so much volume and automation, so long as you choose common options they can squeeze your little 10cm square board onto a huge panel with hundreds of other orders and it costs them almost nothing. The guys with the bigger boards are paying the cost of taking the ppanel through the process. Given the pricing I imagine they still don't receive enough of these tiny board orders to use up all the wasted "offcuts" from larger boards.

You'll see that if you change the options that sometimes the cost jumps by an order of magnitude - that's what you get for not fitting on someone else's panel!

Quote:

Not me. The frugal (my wife says "cheap") Irishman in me compels me to repeatedly go over my layouts looking for anything that might be questionable. I try to get it as close to perfect as possible before I send in the Gerbers.

I'm like that too, I can't bring myself to order PCBs that I'm not sure about. However cheap they are, it feels wasteful, I'll just have to throw them away or use them as coasters or something like that. And as a hobbyist I also enjoy the process of obsessing over the design, doing the best job I'm capable of, even if it's costing me more time than that's worth.

[ThePhysicist]

Does anyone have an idea what to do with the surplus boards? Every order from pcbway has a 5 piece minimum - what do you do with the remaining 4?

[BigDumbDinosaur]

ThePhysicist wrote:

Does anyone have an idea what to do with the surplus boards? Every order from pcbway has a 5 piece minimum - what do you do with the remaining 4?

Use them to improve your SMD soldering skills, or take them to an electronics recycler for disposal. Or, build a second unit for those times when you goof and blow up the first unit.

[BigEd]

(There might be a forum member who'd be interested to follow along, starting with a bare board.)

[gfoot]

BigEd wrote:

(There might be a forum member who'd be interested to follow along, starting with a bare board.)

A while back I made a breakout board for an ARM2 processor, and somebody contacted me interested in trying it - it was expensive international postage, so kind of a hassle to package and send, but they were willing to pay the costs themselves so I sent a couple of boards over. Much better than having them go to waste!

[plasmo]

I'm working on the idea of 10-in-1 where a single board design can have up to 10 different functions depending on how the board is populated and jumpered and how the CPLD is programmed. It is for multi-board modular system like RC2014.
https://groups.google.com/g/retro-comp/c/bt5pVneks0E
Bill

[gfoot]

plasmo wrote:

I'm working on the idea of 10-in-1 where a single board design can have up to 10 different functions depending on how the board is populated and jumpered and how the CPLD is programmed. It is for multi-board modular system like RC2014.
https://groups.google.com/g/retro-comp/c/bt5pVneks0E

Nice! I was musing on something similar but much less ambitious, without the PLD. I'd settle for ROM/RAM vs 6502 options on a single board, with address decoding configured by jumpers. Then three identical boards basically form a base computer, and you can plug more specialised ones on for other things. Dealing with overlapping footprints of even more ICs seems quite challenging!

[jmthompson]

ThePhysicist wrote:

Does anyone have an idea what to do with the surplus boards? Every order from pcbway has a 5 piece minimum - what do you do with the remaining 4?

PCBs make interesting little art pieces too, especially if you panel a few different ones together. I have a piece of my office wall next to my desk where I mounted some broken and obsolete PC motherboards, and it looks pretty nifty.

[BigDumbDinosaur]

BigDumbDinosaur wrote:

floobydust wrote:

How soon do you plan on having the first PCB built up?

I haven't decided. I usually "sleep on it" for a couple of days and then review my work before ordering PCBs.

A paying programming project got in the way for a few days but I finished it yesterday and if you can believe the client, "the check is in the mail." The PCBs for V2.0 have been ordered.

Along with the boards I ordered a stencil, which added less than 10 dollars to the order. V2.0 has seven SMT devices, down from the nine on POC V1.3, so there is still a fair amount of precision soldering required. As the initial objective is to get V2.0 running in a stable fashion, the SMT hardware on the first unit will be installed the old-fashioned way...with a soldering iron. As I did with V1.2 and V1.3, I will enlist help for this step of the build. Once I get V2.0 running I will return to an earlier project.

Much as I appreciate the help in getting these projects constructed, the reality is I am an obstreperous curmudgeon who has long avoided being dependent on anyone when it comes to building stuff. With that in mind, the plan is to see if I can build a second copy of V2.0 using reflow—once the "hand-built" unit is running to satisfaction. Hence the purchase of the stencil.

As I said in the "reflow for dummies" topic, the process I used for the actual reflow seemed to be okay. The problem was too much solder paste was applied and I ended up with bridges everywhere. So I'm hoping use of a stencil will make for better control of solder paste application and result in good joints on all pins.

Aside from wanting to not have to depend on others to do my SMT soldering, I would like to be able to use CPLDs with higher pin counts to add circuit features. While the Atmel (Microchip) CPLDs are available in PLCC-84 packages, those consume quite a bit of real estate. Plus it appears PLCC is going the way of the dinosaurs. So the plan would be to use a QFP package, which on the ATF1504AS CPLD, provides 64 uncommitted I/O pins.

Stay tuned.

[floobydust]

Woo-Hoo! PCBs in shortly then... will be interesting to see how the first one works out.

I'm out of town the past 2 weeks and another before getting back to my lair... but parts have been coming in from multiple places, Mouser order arrives tomorrow. Thankfully my son lives nearby, so he swings over and gets the mail and packages (and pinches a bottle of vino for his trouble).

I should have everything in stock to put together an initial 3.3V system, albeit not a SMT setup, sans a couple SMT chips mounted on DIP adapters.

I'm also very picky about anyone helping me with anything... so I tend to do everything (myself)... not sure how many more years that can last...

[BigDumbDinosaur]

floobydust wrote:

I'm out of town the past 2 weeks and another before getting back to my lair... but parts have been coming in from multiple places...my son lives nearby, so he swings over and gets the mail and packages (and pinches a bottle of vino for his trouble).

A whole bottle of fermented grapes for picking up some bills and boxes? My, you're generous.

[floobydust]

BigDumbDinosaur wrote:

floobydust wrote:

I'm out of town the past 2 weeks and another before getting back to my lair... but parts have been coming in from multiple places...my son lives nearby, so he swings over and gets the mail and packages (and pinches a bottle of vino for his trouble).

A whole bottle of fermented grapes for picking up some bills and boxes? My, you're generous.

Haha... well, he is my Son and he brings over some nice wines now and then too... plus he tends to look after the house when I'm traveling. In any case, I told him to grab one of these:

Simple motto... "life's too short to drink cheap wine, eat bad food and drive crap cars". Life costs $$, you can pick to spend $ or $$$$... usually the more $'s, the nicer it is, who new.

[plasmo]

floobydust wrote:

Simple motto... "life's too short to drink cheap wine, ...

Speaking of cheap wines: I make my own wines. Have a small vineyard that produces 50-75 gallons of wines a year. I'll be busily harvesting grapes and making wine in 3 weeks.

I also make my own (cheap) labels by stick a piece of duct tape over the bottle. I'm proud of the cheap labels; my place is known as "Duct Tape Winery".
Bill