Unusual functions of cheap parts

[Henry Kiefer]

Can you give details?

- Henry

 

[John Larkin]

Can you give details?

- Henry

I posted some opamp schematics to abse a while back. I guess I could
do it again if they're no longer available.

The others chould be fairly obvious.

John

 

[Boris Mohar]

And optocouplers can do interesting things:

Very simple high-voltage opamp, up to 400 volts p-p.

Isolated totem-pole driver, from a few volts up to 400.

Current limiter.

Low-leakage diode, sort of like an LED painted black.

John

A latch.

 

[Martin]

As an addition to the various mentions of common diodes as varactors
there is a well publicized British design for a frequency tripler that
will put out 2 watts at 1.3 GHz and uses five 1N914's in parallel.

I once built an HF transceiver that used CMOS logic chips for all
functions except an audio low noise amp and a voltage regulator...with
further thought those two could likely be done with CMOS logic too.

At least the audio amp, this is nice to build with some Inverters (4069)
with resistive Feedback.

 

[Martin]

Am Fri, 25 Nov 2005 22:13:38 -0500 schrieb Phil Hobbs

As a boy, I used an electric teakettle as a ballast for a two-D-cell
carbon arc lamp--worked great.

An electric arc with just 3V from two D-cells? I thought the arc needs at
lesat 20V burning voltage.

 

[Phil Hobbs]

Am Fri, 25 Nov 2005 22:13:38 -0500 schrieb Phil Hobbs

An electric arc with just 3V from two D-cells? I thought the arc needs
at lesat 20V burning voltage.

It ran off 120 V. Parse the sentence as "two D-cell-carbon arc lamp." An
earlier poster talked about building AC-powered arc lamps using the carbon
rods from dry cells.

Cheers,

Phil Hobbs

 

[John Larkin]

A latch.

Right, if CTR > 1.

John

 

[Martin]

Am Sat, 26 Nov 2005 16:16:27 +0000 (UTC) schrieb Matthias Weingart

To save power, use the LEDs of a backlight to measure the ambient light
to decide to switch the backlight on or not.

But how to decide to switch it off? I think there you have to sample -
switch of for a short time and test. This could give a flickering
backlight.

 

[David DiGiacomo]

Bob Pease of National Semi mentioned a ONE AND ONLY transistor circuit
above/under voltage rail converter (with detailed theory). I cannot remember
the details. But interesting if sometime a slightly voltage behind the power
rail is needed. For example to power a CMOS Opamp now doing rail-input.

For a good discussion of Bob Pease's "April Fool" negative voltage
generator, see:

http://www.edaboard.com/viewtopic.php?p=423522

Unfortunately you have to log in to the site to see the drawings & photos.

I don't think it produces nearly enough current to power an opamp.

 

[Matthias Weingart]

But how to decide to switch it off? I think there you have to
sample - switch of for a short time and test. This could give a
flickering backlight.

Ok, you found the skeleton in the closet. You can not use
this method to switch it off - but it is not required in most cases.
Think of a cell phone - the backlight goes on every time you press a
key, and it is going off after 10 seconds.

M.

 

[Martin]

Am Sun, 27 Nov 2005 09:57:23 +0000 (UTC) schrieb Matthias Weingart

Ok, you found the skeleton in the closet. You can not use
this method to switch it off - but it is not required in most cases.
Think of a cell phone - the backlight goes on every time you press a
key, and it is going off after 10 seconds.

OK, so you can decide to not switch it on and save some mAs.

 

[Fred Abse]

Did you know that a carbon arc acts as a negative resistance? Run the
arc on DC and put an LC tuned circuit in series with the arc (coil of
heavy copper tubing) and you have a powerful oscillator.

Early marine transmitters did it that way.

 

[Fred Abse]

In the silent film era, actors had eye problems due to the UV
radiation from arc studio lamps.

Known as "Klieg Eyes", (from "Klieg Lamp")

 

[[email protected]]

At least the audio amp, this is nice to build with some Inverters (4069)
with resistive Feedback.

Most of the audio section was done that way. But the product detector
had low impedance output and the CMOS amp was too noisy at 50 ohms. A
transformer might have done the job but a common-base amp seemed more
practical and less prone to picking up hum.

Steve

 

[Martin]

Am Sat, 26 Nov 2005 22:35:18 -0500 schrieb Phil Hobbs

It ran off 120 V. Parse the sentence as "two D-cell-carbon arc lamp."
An earlier poster talked about building AC-powered arc lamps using the
carbon rods from dry cells.

OK I liked to do that myself, but not from our 230V mains power, but
with a transformer, 22V, and 30A short circuit.

 

[Winfried Salomon]

Hello Jim,

Jim Thompson wrote:
[...]

btw, do you know a standard complementary pnp-transistor for the 2N2369,
such like 2N3905 but with higher ft and less feedback capacitance? It
seems that the manufactorers have almost no data on their internet pages.

[...]


A 2N2369 is a gold-doped NPN, gold-doped to kill storage time and
improve recovery from saturation. I don't recall any PNP device with
gold-doping... or the equivalent.

thank you, then I suppose the 2N3905 oder 2N2905 are fitting for a large
signal amplifier.

mfg. Winfried

 

[Rich the Newsgroup Wacko]

Take apart a couple of D cell carbon-zinc batteries.

Wash off the carbon rods. Put each in a wooden clothes pin and connect the
attached ends to the mains voltage (US customers only, please).

Tap the free ends of the rods together. Move them apart as necessary. Very
bright! Much brighter than you are.

I put mine in series with Mom's iron, but the thermostat kept turning
it off.

 

[Rich Grise]

One of the MIT EE course videos on the web shows a demonstration of AC
across a pickle... it is an interesting effect. Not sure how the pickle
tastes afterward. Cooking hotdogs with AC is similar, but the pickle gives
off a much nicer translucent flickering glow. Very pretty.

But who wants a cooked pickle? ;-)

Thanks,
Rich

 

[John Perry]

...

But who wants a cooked pickle? ;-)

My ethnic Russian daughter-in-law, just arrived from Tatarstan, made a
Russian soup, into which she chopped several dill pickles.

Wonderful stuff!

John Perry

 

[[email protected]]

Jim Thompson skrev:

I've used a light bulb in series with a rectifier to charge a car
battery (just make sure that line ground goes to chassis ground ;-)

I've seen several speakers where there was a light bulb, in series with
the tweeter, as a power limiter

-Lasse