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KC9UDX
July 21st, 2015, 07:17 PM
If you ever needed a mains frequency stroboscope for adjusting motor speed, here is something you can do in a pinch.

Assuming you have an AC wallwart somewhere, an appropriate resistor, and an LED, connect them in series and power up.

I find this very helpful in areas flooded with various light sources where a simple fluorescent bulb won't work so well. I use my AC bench supply, but it occurs to me that a wallwart would work just as well.

Chuck(G)
July 21st, 2015, 08:05 PM
...or a simple NE-2 lamp and a 33K resistor on the AC line.

KC9UDX
July 21st, 2015, 08:16 PM
Very true.

Chuck(G)
July 21st, 2015, 09:26 PM
You can still find neon night lights in just about any hardware, big box, or drugstore.

If one is determined, it's possible to build an optical tachometer with an old PC and a few parts feeding a parallel port. Or build one from just about any small MCU--even the 8 pin ones would work. I used to calibrate my film camera shutter speeds with an IR LED and phototransistor connected to a parallel port on a PC.

That's one of things that's fast disappearing from today's PCs--the plain old parallel port (and access to it). A darned useful and very simple thing.

g4ugm
July 21st, 2015, 11:06 PM
Not an FPGA , MOS FET and LED? Mind I did want 120 FPS for a teleprinter...

Doug G
July 22nd, 2015, 01:14 PM
I plead ignorance. What's a wallwart?

KC9UDX
July 22nd, 2015, 01:22 PM
Wallwart courtesy Wikimedia:

25480

griffk
July 22nd, 2015, 01:53 PM
If you ever needed a mains frequency stroboscope for adjusting motor speed, here is something you can do in a pinch.

It wouldn't be 60Hz in Europe -- probably 50Hz, and not really adjustable without a PLL and a bunch of esoteric divider/harmonic choosing circuitry, but it could come in real handy to tune a clock motor, or something that locks to the mains freq. -- very nice!

gwk

KC9UDX
July 22nd, 2015, 02:04 PM
Right, it will be whatever your mains frequency is, or, double with the neon.

Most things I've found that need to be adjusted this way have both separate rings for 50Hz and 60Hz. Some turntables are even this way, especially ones manufactured within Europe.

A simple microcontroller, like a BASIC Stamp, or Arduino, or the likes would make a very simple and nice adjustable one.

griffk
July 22nd, 2015, 02:09 PM
If one is determined, it's possible to build an optical tachometer with an old PC and a few parts feeding a parallel port.
That's one of things that's fast disappearing from today's PCs--the plain old parallel port (and access to it). A darned useful and very simple thing.

You're right - and it's so sad that as PCs have become more "sophisticated", their I/O has been dumbed-down to the point that they are MUCH less useful, as general purpose devices. Even though the lay population probably uses/used these ports only for traditional peripherals, they are essential for things like 3D printers/CNC, PLC control, talking to many HH devices, etc, etc., and specially - INSPIRING CREATIVE USE BY YOUTHFUL EXPERIMENTERS/ENTREPRENEURS!

Even today, RS232 and Parallel I/O have so many generally useful attributes, that I actually LOOK for their inclusion on a PC (specially a laptop), and it becomes a deal maker or breaker, if I can or can't find a model with these I/O inclusions...

gwk

njroadfan
July 23rd, 2015, 03:59 AM
I still insist on having a real parallel and serial port. It comes in handy for things like this. Good thing is they still come on new motherboards. I even spotted them on previews of the latest crop of Skylake Z170 chipset motherboards!

Doug G
July 24th, 2015, 04:56 PM
Wallwart courtesy Wikimedia:

25480
Thanks. That was my guess, but never had heard that name before.

roberttx
August 13th, 2015, 05:29 AM
If one is determined, it's possible to build an optical tachometer with an old PC and a few parts feeding a parallel port. Or build one from just about any small MCU--even the 8 pin ones would work. I used to calibrate my film camera shutter speeds with an IR LED and phototransistor connected to a parallel port on a PC.

I already have two optical tachometers, a digital one that I use in my day job to check centrifuge speeds and a clockwork one that I have just because. Despite that, I'm still tempted to have a go at this!

The comments about RS232 & parallel ports are very true. In some areas, it goes further than that - 286 & 386 PCs, running DOS, are sought after in the ham radio world because they're used to program older 2 way radios, like the Motorola Jedi series. The programming depends on precise timing in the UART and Windows screws it up.

KC9UDX
August 13th, 2015, 06:17 AM
. The programming depends on precise timing in the UART and Windows screws it up.

Careful, I got blasted for blaming Windoze for that. :o

g4ugm
August 13th, 2015, 07:39 AM
Its more complex than "windows screws it up". Firstly its DOS software that assumes its running on slow old hardware. So not only won't it work under windows, it won't work in real DOS on a quick(ish) machine. I believe Motorola will supply more modern software at a price that makes it cheaper to buy new radios. A sort of corporate RansomWare perhaps? Just like the games in windows/10 & android where yu have to pay to remove the adds....