push-push on/off switch

Well, I posted a simple circuit that does interesting things. Some people dispute that it can work as an on/off switch, so I guess they think that I'm delusional or that I'm lying. Some people have simulated it, couldn't get the sim to work, ditto. Some people claim it's no good because it doesn't meet their standards of whatever. Some people claim it will fry the fet, without consideration of the load impedance or fet size.

What nobody seems to have done is tried it. Or even thought about it very hard.

I'm not ruffled, I'm amused. Both by the simple circuit, and the very complex reactions to it. Like I said, I take business away from people who refuse to think. That's not a threat, that's a fact.

No.

John

[snip] [snip]

But John, You didn't answer my question regarding its application in any product you ship.

"Working" and good engineering practice are two different animals.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

The 100K resistor and input charge should provide adequate protection. A spark gap is included as part of the PCB design.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

I never said I use it in a product I ship.

As far as I can tell, "Good engineering practice" seems to mean "that's the way I'd do it."

John

"that's the way I'd do it." In a product? You're being a sore loser, John. You know you'd never "engineer" that "design" into a product ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

Good grief, I posted a cute little circuit with four parts, and everybody is getting mad at me because they can't understand it.

John

[snip]

I understood the "cute little circuit with four parts", saw the flaws, and said so.

Why don't you elaborate on your "cute little circuit with four parts" and make it bullet proof?

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

So what would make you happier, a Pic driving an ssr?

John

On a sunny day (Mon, 22 Oct 2007 19:14:36 -0500) it happened Spehro Pefhany wrote in :

Yes, but sound a bit tricky. I have had inch like sparks after walking on the carpet in the reception and then touching a PC. I estimate 10kV is *possible*.

10kV in 100k is 100mA. Will the spark gap be fast enough? Perhaps not a simple spark gap, but a neon bulb, to limit at about 70V? Not sure how fast a neon is though.

Or you could just go to 1M or 10M.

--

John Devereux

I know it works. I've been playing with MOSFETs myself. It still make a good "April's Fools" circuit.

robert

Larkin

It builds up from noise like any other oscillator. Just kT/C noise is enough--if you're epsilon volts off equilibrium to start with, on the second press you're Av*epsilon, on the third press you're Av**2 * epsilon, and so on. If you have voltage gain as low as 10, it'll take a dozen pushes or so to get to full scale. A bit of hum pickup will get you started a bit faster.

Cheers,

Phil Hobbs

Fast isn`t much of a factor when you have power MOSFET gate with a large resistor in series with the gate. There`s something like a 10n capacitor equivalent in there in terms of charge. It`s a much more challenging thing to make the gate change rapidly when you have to.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

On a sunny day (Tue, 23 Oct 2007 09:21:46 -0400) it happened Spehro Pefhany wrote in :

Yes, you are right! Should have seen this :-)

On a sunny day (Tue, 23 Oct 2007 09:21:46 -0400) it happened Spehro Pefhany wrote in :

But now the next problem: I hold my finger on the middle pad, the hum switches the load at 50 Hz (or 60 in the US).

Perhaps just the flip flop is a safer idea... Dirt, moisture, can cause problems too.

Philips once had TV with 'touch' buttons to select a channel, flee lands on it ..... I have seen them auto-change channel too. Those were like this -- - -- where the finger was supposed to connect the center electrode to the outer ones. They had some chips to drive that, use to break down....

I prefer buttons that need a real force, click, and give some motion feedback. Good PC keyboards I have not seen since the old IBM ones with springs in it.

Hardly, I'd replace the whole thing with a real push-on/push-off switch, and forget all the exotic electronics ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

in the US).

Of course it`s a safer idea, but what I suggest will work on the bench. A 2 cent BAV99 will absolutely protect the gate with a reasonable series resistor (physically large and large value) if you want to make it bulletproof. Or use a MOSFET with an internal zener.

A feature.

Anything that comes into contact with an operator is a candidate for damage- physical or electrical.

The current ones are amazingly good considering how cheap they are. But nothing compared with the IBM keypunch keyboards.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

I posted the circuit because it's interesting, at least to me. The follow-on interesting thing is people's reaction to it, specifically hostility, and inability to understand how it works.

I'm sure glad I posted it.

John

Larkin

In open air, with stray e-fields, and a bit of temperature driven gate threshold change, 5 hits will usually rail it.

If you hold down the button, to bias the fet partly on, and release it, it can take days for the drain current to drift very much.

With an spdt switch, the external cap can be quiescently in parallel with the fet g-s thingie (I almost said "junction") so it could be made to be stable for months at least.

John