this is getting crazy

It seems to me that the cheapest way to configure a ram-based FPGA is probably to use a uP and an eprom... cheaper that a single serial eeprom, and you get to use the uP for other tricks.

Or probe one.

John

Fluke has a new handheld thermal imager, only $10K, about 1/3 the price of such gadgets up to now. Tempting.

John

True. I have seen boards with a test pint on every node for "bed of nails" or "flying probe" testing.

Boring, Oregon? Waterproof, Louisiana?

John

Hello Terry,

Is that what Maoris would say? Nice. Sounds much better than hello.

Same here. I found that uCs are still not competitive in many designs where they would fit nicely. I don't know, possibly the semi mfgs try to maintain higher margins but in the end it hurts sales. Whenever I contemplated migrating one of my high volume designs to uC it turned out costing more than the huge pile of SMT on the discrete+logic solution.

Yes, except when I have to solder one of those MSOP or TSSOP packages.

Regards, Joerg

I have a simpler solution: Mike, help.... Ah, the joys of knowing computer geeks.

Cheers Terry

Hello John,

Well, yes, if you have big iron like that on the board the cost of any uC will seem like a mere pittance.

Oh yes. Bzzzzt .... POP. After that it's unsoldering one of those 100+ pin devices without messing up the pads.

The other issue is that it is so easy to miss a bridge. You wonder why the board doesn't work like expected, detect a whiff of "ampere smell" and suddenly find out that one of the chips is as hot as a halogen bulb.

Regards, Joerg

:)

unless you're a minimalist, in which case you're probably more competitive.

Cheers Terry

Hello John,

You might even be able to modify a cheap digital camera for that. I built a CCD camera from scratch as my master's project in the 80's. I had to try hard to reduce the IR sensitivity, meaning expensive optics. Else you could hold it out of the window and see whether someone in another building in the distance was smoking. You could also "see" a person in a pitch dark room. It was amazing.

Regards, Joerg

Not a problem, I've "changed" such IC's in under 5 minutes! Probing, make sure the probe is nice and sharp. Most newer Tek scope probes are sharp enough. The biggest problem I find is keeping track of which pin to probe - it's easy to miscount a pin or two when all the traces look identical and there are 20 to 50 pins on each side spaced 0.5 mm apart.

"There are rarely too many test points or ground lugs."

The corollary is "There is never any space left for sufficient test points and ground lugs" :)

I always try to add sufficient *easily accessible* test points, but I am sometimes thwarted by the size contraints imposed by the product.

I just finished a board (small really - about 700 components, 100mm x

60mm) and there are over 300 test points - but they are the 0.035 inch variety so they can fit. Some of the parts on there are quite large (we still have a long way to go in miniaturisation).

Cheers

PeteS

I used to use ultrafine "Sharpie" markers in red and black to mark every fifth and tenth pin in alternating colors down the side of a chip to help keep track of pin numbers. A Q-tip and IPA removed the ink when I was done but it made troubleshooting a lot easier.

--
Link to my "Computers for disabled Veterans" project website deleted
after threats were telephoned to my church.

Michael A. Terrell
Central Florida

Hello Michael,

IPA? I didn't know that India Pale Ale removes Sharpie marks :-)

Regards, Joerg

Indeed it is. the first bit is pronouned "key", the ora rolls the R

especially the CD4000 series.

In this cxase it was a Cygnal cpu, a lightning fast 8051 derivative. Thats the 2nd such (bad) design in a row I have seen. the first was the LED video screen. That pissy little 8kb 8051 gets beaten to death doing

24-bit arithmetic, and costs us $0.50 *more* than a 32-bit TI DSP with far more peripherals.....

indeed. thank Zeiss for binocular microscopes.

Cheers, Terry

even SOT23s are bad. No thermal mass = instant death. tack-soldering dangly wires aint so easy either.

Cheers Terry

John wins the competitive PCB layout stakes :)

in the early 90's we played an april fools trick on the PCB assy staff. We got the prod. and Q. mgrs to come up with the appropriate documentation, then gave the head of PCB assy a tube of SOIC14 74HC14s to use in lieu of DIP14, saying they were the only ones available. An hour later, Shannon and her ladies had soldered the entire tube onto PCBs, beautifully done. They'd placed a small spacer under the chip, and wired them in with stripped W/W wire then glooped over it. The prod mgr saw this, and exeplained the "joke". She wasnt amused, and hit him in the stomach, hard enough to knock him to the ground (small guy, big lady). IIRC we used the PCBs that way

Cheers Terry

Or the maldives? Or Jupiter? I like this game :)

Cheers Terry

one TP for every meaningful node on the PCB. After the hassles we went thru laying out the PCB twice, this was the last thing on our minds.

Cheers Terry

I put little markers by every tenth pin, and write down one of the numbers at each corner. As well as a rectangular pad for 1, rounded rectangles for the rest.

I've seen some consumer stuff with silk-screen on the underside. great for techs, esp. when they write down test voltages, waveforms etc.

Cheers Terry