Help Please -- very strange oscillator problem

[snip]

We need to see your _actual_ circuit.

If you will follow my previous instructions... send me an E-mail via the envelope icon (NO ATTACHMENT)... I will reply with an address you can use to send the attachment.

Once I receive your schematic I will post to my S.E.D/Schematics page for all to see and comment on. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson
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Me: But if it ever gets into state 14, it hangs up.

Them: It can't get into state 14.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

I'm with Jim here, we need a schematic.

One thing that always bothers me with this circuit is the base-emitter breakdown, where the circuit can shovel amps into the opposite base-emitter junction.

The fact you mention 10V spikes and 12V centre tapped coils suggests you haven't taken into account of the 7V BE maximum rating.

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Mike Perkins 
Video Solutions Ltd 
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Reply to
Mike Perkins

Yep. Some people just can't handle "what ifs". ...Jim Thompson

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

Limited understanding. They only get as far as how they think it oughta wor k.

Them (I don't remember exact phrases, it was a long time ago): It's complet ely secure, there's no way in. We've gone over it all. Me: If you cycle the power on the server it assumes all connected machines have authorisation to access whatever account they say they have access to. And due to the slightly odd electrical layout end users can remotely cycle the power. And are now doing so.

NT

Reply to
tabbypurr

OP didn't notice that the schematic I posted was more or less the same one as his, except in his version he probably has the coils taps on either side of the center connected as the collector loads.

Also the one I posted has some extra resistors and diodes and if the circuit is going to work at all with an inductive load those are kinda important.

Reply to
bitrex

I use GMail for all personal communications and the project I am discussing here is my side work, quite different from what I do at work (telecommunication equipment firmware). I have tried using Dropbox before, but found it very wierd. I would load files, but the intended receiver would not be able to download them.

Please send me a one word email to my GMail address( snipped-for-privacy@gmail.com) and then we can ' start exchanging emails.

Reply to
dakupoto

In my implementation, each 2N3055's emitter is grounded SEPARATELY via a 10 Ohm 10 Watt resistor to limit the collector current. So, the issue of one transistor emitter shovelling current into the other does not arise. Please also note that a copy implemetation of the misbehaving circuit works fine.

Reply to
dakupoto

Please also note that a

start swapping parts and report back when you have identified the swapped part that "follows" the problem.

m
Reply to
makolber

There are some FIR filter implementations, done in an FPGA, that assume years of high-clock rate (trillions) of absolutely correct adds and subtracts. Any errors or glitches make permanent offset or end-around errors.

They seem to work.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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Reply to
John Larkin

Fixed-point adds and subtracts are error-free. Floating-point multiplication introduces quantization error, and of course floating-point adds and subtracts lose the LSBs of the smaller operand.

Cheers

Phil Hobbs

Reply to
pcdhobbs

A fir boxcar (sinc filter) has a FIFO and a subtractor and an accumulator. You initialize everything to zero and start clocking. Nothing can go wrong, someone said.

That one bothers me, but it seems to always work. Emotionally, I prefer an IIR filter with some feedback.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

Well, if you want it normalized to another gain, you're likely to lose LSBs in that conversion. (Hopefully you perform the multiplication after the accumulator, so the error does not also accumulate.)

If you want a better filter profile than sinc, you'll lose bits. A 1-3-3-1 is about as good as you can get with integer coefficients. Beyond that, you need arbitrary multiplications, and either a double width accumulator or acceptance of rounding.

IIR must lose bits because of the repeated multiplications.

But I suppose DSP theory isn't "worth reading".

Tim

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Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
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Reply to
Tim Williams

Integer adds and subtracts are exact modulo 2**N. Multiplication and division produce results with more bits than they start with, so even with extended precision FP registers, you have to round at some point. It's the rounding that produces the LSB/sqrt(12) RMS additive noise, and that's why accurate long-term numerical simulations of chaotic systems (exponential noise amplifiers) are impossible even in principle.

Symmetric FIR filters are pretty useful. IIRs can have limit cycles and stuff, so you have to be careful with them.

Sometimes you can usefully factor a filter into an IIR part and a FIR part. The Footprints sensor's actual measured quantity was the first finite difference of the temperature of each pyroelectric pixel with 5 Hz sampling. There was a thermal rolloff caused by the thermal mass of the suspended film and the very low thermal conductance, so it had a weird peak with rolloffs on both sides.

I was using a MCU with 902 bytes of RAM (PIC17C756A), and the inverse filter for that transfer function needed to be over 20 samples long, for each of 96 pixels, so it wouldn't fit. I worked out how to factor it into a 4-sample FIR followed by a one-pole IIR lowpass, so it all fit, though not by much.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

The problem was with a bad 4 cm long wire. As the most popular variety of 2n#055 comes in a

1 mm thick metal case, a thicker heat shield must be used, and it is difficult to mount the two pairs of this combination on the PCB. in my case, the two transistor-heat shield pairs are mounted on a small strip of phenolic. There are short wires connecting the capacitor-diode-resistor network with the two 2N3055s. The wire to the base of one 2N3055s was bad. No bad transistors or incorrectly connected diodes.
Reply to
dakupoto

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