design help

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Aha! A rare occasion. You actually ask a cogent question rather than baiting.

Flyback diodes DO increase the time it takes for the field to collapse. I don't know what effect it has on _opening_time_of_contacts_ (slew rate), but it certainly inserts a _delay_ in opening.

In CMOS relay driver chips that I designed for Ethernet use many years ago I did the following (for two reasons):

(1) Diodes, for flyback use, don't exist on a CMOS process that don't also have nasty parasitic (and destructive) current paths.

(2) Speed was of the essence for releasing the relay.

So I devised a scheme where the voltage was allowed to rise as much as safely possible on the output device, then turn it back on to prevent further rise (in essence an active clamp).

Since this allows significant reverse voltage on the coil, the field collapses much more quickly than with a flyback diode.

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Jim Thompson
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I used to use both drum and chain printers, back when I ran a PDP-11 based "computer center" (RSTS/E timeshare OS, lots of local and dial-in dumb terminals.) Yeah, they were a kick. Some of the higher-end printers shot out paper so fast they needed power paper folders. Huge and noisy! Cost lots more than a good car, back then.

John

Reply to
John Larkin

As in...

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Done so long ago I was using OrCAD Capture under DOS ;-)

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Jim Thompson

I recently did...

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which has over 250 distinct serial ascii commands, and I'm just finishing a serious upgrade to this,

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which is code I hadn't touched for about two years. Organization and commenting are a lot more important than languages and tools.

We're advertising for an embedded products programmer now. I got about

100 resumes from a Craigslist ad. Most are high-level types, Windows/Linux/Ruby-on-rails/SQL/Web/C++ types, totally abstracted from the CPU and hardware itself.

About 5 of the applicants look worth interviewing, and they are all old farts like me. Kids these days!

John

Reply to
John Larkin

When I was a kid, I tried making a transistor from two diodes. I bet lots of people have done that.

I wonder if you could make a point-contact transistor from rusty razor blades or something.

John

Reply to
John Larkin

Brilliant observation. Why didn't I think of that?

John

Reply to
John Larkin

We used the Data Products drum printers at Cincinnati Electronics for the SATE booths for the PRC-77 man pack radios. The tests were run by some four bit Data General computers, and we used model 33 teletypes for data entry. When the engineer from Data General did a memory dump, the paper hit the ceiling, and spilled out the door open of the computer room.

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Michael A. Terrell

Even to an indecent font.

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Michael A. Terrell

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Jim Thompson

On a sunny day (Sat, 28 Feb 2009 09:55:21 -0800) it happened John Larkin wrote in :

A question, just to break in here, but relevant to this discussion.: Do you also provide the PC side, with some sort of GUI, or does the customer have to learn ad dig all RS232 commands to be able to for example create a simple pulse?

In my view both are always together, unless fro very very specific cases where the customer does not _want_ the GUI.

All other projects I have done had both a PC side software and an embedded side. The PC side can be very very complex, I like to put as much there as possible, because it has no constraints as far as memory and speed is concerned.

A simple example is 'col_pic', the embedded side drives the LEDs, and is controlled via RS232 from a GUI, or audi processor:

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Without the PC side where would the user be? Like a car with engine but without dashboard :-)

Reply to
Jan Panteltje

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What a liar you are.

I clearly remember the first problem you had with relays (here) was that
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John Fields

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

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You\'re not _asking_ anything, you\'re _asserting_ that not using flyback
diodes will increase the armature\'s acceleration.
Reply to
John Fields

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Jim Thompson

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Yeah.

I\'ve used it before as a switch debouncer.
Reply to
John Fields

TWO old hens.

John

Reply to
John Larkin

| James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

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| 1962 |

Actually, endless, content-free repetition is often an earlier sign.

John

Reply to
John Larkin

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Who cares?

JF
Reply to
John Fields

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I read an article a few years ago where some guys achieved the same
results using Zener diodes rated somewhat below the transistor\'s
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Reply to
John Fields

How did that get to be an issue? Of course it doesn't need a flyback diode; that's 200% obvious.

And, as previously noted, several other people posted very similar "crummy" circuits, so go cluck and peck at them them, too. You posted a series of ever-more complex 555 things, most of which had problems.

For sure. It shows the contact closing threshold as zero coil current. It absolutely does not illustrate or explain the GOOD/NOT GOOD concept. Clearly made-up stuff by careless people. So, useless as an authority reference.

Since I've only asked questions, I can't be "right or wrong." I can maybe get answers and learn stuff.

I've got a few serious problems to work through this weekend (some exploding power resistors, more firmware, cleaning up downstairs and The Ratmobile for a visitor, some family stuff in Sausalito) but I may play with it. If not, next week maybe.

It's like the Variac thing. As Wernher von Braun famously said, "One experiment is worth a thousand expert opinions."

John

Reply to
John Larkin

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