Bread Board Backers

[tggzzz]

Oh, come on! the TIS1040 puts out 3kV at 160kHz, probably a nasty waveform at that. 

You and tooki may get off on this constant argument but it's getting kind of tedious for the rest of us. That 'demonstration' has put you down in my estimation.


P.S. It only takes a couple of pF inter-strip capacitance to pass enough current (the TIS1040 is limited to 7uA) to perform that little trick without needing any insulation breakdown.

You omit to mention he other very important characteristic: the source impedance. That is what will determine the voltage seen at the device terminal. The manual, such as it is, is unclear about the source impedance. Certainly touching the exposed termjnal with ringers produces no sensation whatsoever.

Of course the leaf capacitance is of to be of the order of a few pF. That's obvious from simple school physics. But that is sufficient to cockup many analogue circuits, especially those with high internal gain reduced by heavy feedback.

I've no idea why you've invoked insulation breakdown; that never been suggested as relevant.

[tggzzz]

3kV into a breadboard!?!?

No, much less than that, depending on the very poorly defined source impedance, and the dynamic impedance of the neon during breakdown, and interleaf capacitance.

I get much much higher voltages (and currents) from clothing and HiFi equipment. ( I used the latter to make my daughter realise that electricity can bite)

[Gyro]

Oh, come on! the TIS1040 puts out 3kV at 160kHz, probably a nasty waveform at that. 

You and tooki may get off on this constant argument but it's getting kind of tedious for the rest of us. That 'demonstration' has put you down in my estimation.


P.S. It only takes a couple of pF inter-strip capacitance to pass enough current (the TIS1040 is limited to 7uA) to perform that little trick without needing any insulation breakdown.

You omit to mention he other very important characteristic: the source impedance. That is what will determine the voltage seen at the device terminal. The manual, such as it is, is unclear about the source impedance. Certainly touching the exposed termjnal with ringers produces no sensation whatsoever.

Of course the leaf capacitance is of to be of the order of a few pF. That's obvious from simple school physics. But that is sufficient to cockup many analogue circuits, especially those with high internal gain reduced by heavy feedback.

I've no idea why you've invoked insulation breakdown; that never been suggested as relevant.

Please don't make it worse...

Source impedance of the TIS1040 is irrelevant in this situation, it's designed to be effectively a current source (for safety reasons). The voltage would have been the breakdown of the Neon (or LED) plus the drop across the reactance of the inter-strip capacitance at that the operating frequency.

What is the reactance of a 1pF capacitor at (go on, I'll be generous) 150kHz pure sine wave? Take your time. Now how much reactance, and so, how big a fraction of a pF do you need to pass the entire current limit (7uA at 0-5Meg) of the TIS1040 output at 3kV?

I mentioned breakdown, subsequently, because Omega Glory expressed surprise at the 3kV, it's likely that he was thinking about insulation breakdown.

Posting you little neon demonstration without indicating the magnitude of the source was unforgivable. Credit to him for asking the question.

Just for fun, yesterday I was inspired to spend 5 minnutes demonstrating the fun effects solderless breadboards can have. Getting the photo took another 5 mins

This is an unmodified solderless breadboard, a power source, and a neon bulb. As you can see, the power source is connected the left side side of the neon, but not to the right side. The neon bulb is getting enough power to light up, despite being unconnected to the power source.

Such power transfer is more than sufficient to screw up an op-amp feedback loop, etc, etc, etc.

You may claim it was "Just for fun" but you posted it to make some sort of dramatic demonstration of how bad breadboards were, otherwise why bother, when a simple fractional-pF series capacitor would have achieved exactly the same result.

Why did you use emotive language like "power transfer" and "the neon bulb getting enough power to light up, despite being unconnected to the power source." when what you actually meant was, there is a tiny bit of capacitance, as there is in anything. You intended to deceive.

[coppercone2]

highly sensitive circuits are like a small portion of electronics people work on anyway.

you won't get far if you treat everything like that. it's counter productive to just assume everything is super sensitive. This falls into the realm of high impedance electronics.

guess what, in the real world, its often considered a luxury. Real things have lots of wires, murphy goes out and puts nasty wiring thats hard to deal with everywhere. If you learn how to work with it your designs and skills become alot more practical.

[tggzzz]

If you think that "high impedance" and "high voltages" in that demo mean the demo is unrealistic, then let's consider a low-voltage low-impedance circuit that you ought to have studied when learning electronics: a one transistor common-emitter amplifier.

The BJT's collector-base capacitance (C_cb) is, as the excerpt from TAoE notes (p114), usually around 4pF. That is similar to the parasitic capacitors in solderless breadboards.

TAoE goes on to note that C_cb "often dominates the rolloff characteristics of amplifiers, because a typical feedback capacitance of 4 pF can look like several hundred picofarads to ground"

Essentially the capacitance is being "multiplied" by the amplifier's gain. That kind of phenomenon occurs in many circumstances where there is amplification/gain. It is one of the sources of the wry aphorism "amplifiers oscillate, oscillators won't".

Small capacitances do matter, even in simple circuits.

[tggzzz]

I mentioned breakdown, subsequently, because Omega Glory expressed surprise at the 3kV, it's likely that he was thinking about insulation breakdown.

OK; that wasn't clear. Putting the wire on the plastic right next to the strip containing the neon doesn't illuminate the neon, whereas into a strip several rows away does. Hence I don't think breakdown is involved

Posting you little neon demonstration without indicating the magnitude of the source was unforgivable. Credit to him for asking the question.

The large voltages are needed to fire a neon, so a large source is required

Much lower voltages can (and do) bugger up high gain circuits.

Just for fun, yesterday I was inspired to spend 5 minnutes demonstrating the fun effects solderless breadboards can have. Getting the photo took another 5 mins

This is an unmodified solderless breadboard, a power source, and a neon bulb. As you can see, the power source is connected the left side side of the neon, but not to the right side. The neon bulb is getting enough power to light up, despite being unconnected to the power source.

Such power transfer is more than sufficient to screw up an op-amp feedback loop, etc, etc, etc.

You may claim it was "Just for fun" but you posted it to make some sort of dramatic demonstration of how bad breadboards were, otherwise why bother, when a simple fractional-pF series capacitor would have achieved exactly the same result.

Why did you use emotive language like "power transfer" and "the neon bulb getting enough power to light up, despite being unconnected to the power source." when what you actually meant was, there is a tiny bit of capacitance, as there is in anything. You intended to deceive.

Thanks for including and acknowledging the caveat; a less honest person would have snipped and ignored it

Why "power transfer"? Because power is needed to illuminate the neon or LED, and it is transferred!

Much lower power and voltages are sufficient in active circuits, even those that beginners might use. Photodiode amps will often have ~1pF feedback capacitors to get the frequency response[1], and there's the standard common-emitter amp example.

[1] see, e.g. TAoC chapter 4x.3 for many examples, including Fig4x.22 which has a 1pF capacitor around a "jellybean" LF411 op amp, and 1.3pF around a OPA656.

[watchmaker]

Just for fun, yesterday I was inspired to spend 5 minnutes demonstrating the fun effects solderless breadboards can have. Getting the photo took another 5 mins

This is an unmodified solderless breadboard, a power source, and a neon bulb. As you can see, the power source is connected the left side side of the neon, but not to the right side. The neon bulb is getting enough power to light up, despite being unconnected to the power source.

Such power transfer is more than sufficient to screw up an op-amp feedback loop, etc, etc, etc.

Very interesting. What was the applied voltage/frequency, and did you measure how much current was passing through the bulb?

It would be wrong to read too much into this demonstration; its principal purpose is a visually gripping demonstration of power transfer between insulated conductors.

Frequency apparently around 150kHz, voltage and internal resistance are unclear but both are "high" (I hate adjectives ). The "power supply" was a TIS1040 lamp tester. No, I didn't measure the current, either with a meter or my tongue

It also works with a modern high-efficiency LED, but not with old LEDs.

I just got my breadboard from Assembly Specialist.  The weight and contacts are pretty nice.  Because of these posts, I measured the capacitance (w/ my Shannon tweezers) between adjacent rows. The Assemby Specialist (3M) have the highest (10 kHz) at 4.2 pF.  Believe it or not the cheap ones and an older Global Specialty are lower at the same 3.3 pF.

It does not change much if you skip rows.  I can see how these details matter.

[tggzzz]

I just got my breadboard from Assembly Specialist.  The weight and contacts are pretty nice.  Because of these posts, I measured the capacitance (w/ my Shannon tweezers) between adjacent rows. The Assemby Specialist (3M) have the highest (10 kHz) at 4.2 pF.  Believe it or not the cheap ones and an older Global Specialty are lower at the same 3.3 pF.

It does not change much if you skip rows.  I can see how these details matter.

Thanks for the measurements; always better than handwaving!