Speed of Optos on BoBs

[boldford]

What sort of clock rate can I sensibly get through a BoB fitted with EL817s? If too slow, would it be sensible to replace the STEP channels with something like a TLP521 leaving the DIR and ENABLE as is?

[Jonathan]

The opto-isolators are very unlikely to be the limiting factor on a breakout-board as most parallel ports struggle stably to output more than around 35kHz.

[JAZZCNC]

The opto-isolators are very unlikely to be the limiting factor on a breakout-board as most parallel ports struggle stably to output more than around 35kHz.

Actually you'd be surprised how many problems come from slow opto's and I've seen plenty of people on the Yahoo forum have all sorts of troubles with cheap Boards using slow opto's.!!

Must admit Thou personally I've never had any problems.!

[irving2008]

I agree with Jonathan, though it does depend on how they've been used. The EL817 are good to 50kHz+, if driven hard enough, which is better than the parallel port in typical use. The TLP521 isn't that much faster (they both have a 'typical' rise/fall time of 4uS with a 100ohm collector load).

[John S]

I have, breakout boards have been the bane of my life.
Old desktop computer on the router died over the weekend, grabbed a 'new' Pc from up in the hayloft, got a stack up there all bagged and clean genuine install of XP on it.

Got it all setup, nice HP Compact and wouldn't work the router, router was working fine on Friday. Threw it to one side and grabbed a Trusty Dell SX270,used loads of these over the years, absolutely bomb proof.

Still dead.

Go looking in the router box, no charge pump light. Check the output from the Dell with a scope, 4.5 volts dead steady at 17kh.

Short enable down to ground to bypass the charge pump and voilà, all working. only problem is if the router is on whilst it's booting up it jumps all over and the spindle starts and stops on it's own 3 times.

This is about the sixth time I have had different breakout board with charge pump problems. So basically 4 hours wasted because someone who is supposed to know better when they are designing can't be arsed on checking properly.

When you query problems all you get is "Well I have sold loads of these and not had problems "

In the past I have sent 5 boards back that didn't work correctly and they got returned with link wires and extra diodes soldered on over the back and an input stolen so it could amplify the charge pump.
If they are that good why the mods ?

[irving2008]

Because there's a difference between designing for mass production and designing to a specification and a price... I can design and build a one-off that'll be perfect...but it'll be a one-off... if I want to design it so it can be assembled and tested by a team of trained monkeys and is bullet proof to its environment it needs a lot more rigour. I cut my teeth on troubleshooting manufacturing problems at GEC-Marconi on head-up displays and the like... it was rare to get a batch that actually had 100% good ones, in fact there were on occasions batches that were close to 100% failures... With logic circuits its obviously easier to get it right (though the number of SystemX telephone exchange cards I've seen with spaghetti all over the back suggests otherwise.) Designing analogue circuits seems to be a dying art these days. I had a couple of electronics students on work experience not that long ago who hadn't done anything of note with op-amps or even discrete transistors :(

[Jonathan]

I had a couple of electronics students on work experience not that long ago who hadn't done anything of note with op-amps or even discrete transistors :(

Sadly that doesn't surprise me any more. In the first week on my course (Electrical/Electronic eng.) for a bit of fun they gave us a little car thing to put together which involved soldering components on to a PCB. The vast majority had never even used a soldering iron. I can only think of one person, besides myself, out of about 100 on my course in my year who does any electronics at home which really showed when it came to actually making something. That was quite some time as there's not much practical work... Also noticed that the people who had done A-level electronics weren't much better off and didn't seem to know things I'd consider basic, so I'm glad my school didn't offer it since, as it was the subject I was most interested in I would probably have naïvely taken it in instead of further maths.

Anyway, I reckon I'll make a breakout board soon...bought the components ages ago but keep putting it off. How hard can it be!

[John S]

Because there's a difference between designing for mass production and designing to a specification and a price...

Sorry doesn't wash with me, although I hate the term in that it's so misused there is a "Fit for Purpose" clause in that it SHOULD be fit for purpose.

OK anyone can drop a bollock but to keep dropping back on the old excise of "We have sold loads " when you know full well they had had to modify the design three times for faults that I have found and they are still not right.

As son as they hit the marketplace they should work correctly without having to resort to soldering jump wires all over and extra components.

[irving2008]

Not hard at all :) tho not necessarily cheaper than buying one...

[irving2008]

I totally agree... my point was that designing something as a hobbyist then taking it to market is a different ball game to an experienced designer designing for mass production and manufacturing tolerances etc.

One of the key differences is testing. As a 'hobby designer' I'd consider ten or so prototypes tested by friends (or worse, the first dozen or so unlucky punters - were you one of those I wonder) as adequate. As a manufacturer I'd want to build, and evaluate to destruction if need be, several hundred at least before letting them loose...