## Search found 106 matches

Mon Oct 06, 2008 4:26 am
Forum: General Discussion
Topic: Can not find spiral
Replies: 16
Views: 5240
If you've been trying a search for the math, try using "helix" rather than "spiral". Helix is the analytical geometry term for what we usually call a spiral. Dean Dean: I tried helix but they keep stating that helix is a space curve. What i am looking at here is a 2 dimensional curve, if we can act...
Thu Sep 18, 2008 12:02 pm
Forum: General Discussion
Topic: Stringed Instrument Tuner, Ideas?
Replies: 30
Views: 7415
Hi again, ...... The tone output BTW is so the user can tune the string close to the right frequency to start with, then fine tune with the LED strobe. That'a a very good idea, espacially if the instrument is "very out of tune" (like when you change a string). The strobe method can give false readi...
Thu Sep 18, 2008 11:40 am
Forum: General Discussion
Topic: Incandescent lamp longevity at half rated voltage
Replies: 18
Views: 5310
It is allways better to use, for example, two 220 V bulbs in parallel on a 110 V line (at half their nominal voltage) than to use two 110V bulba in series on the same 110 V line.

Plus when one of the bulbs dies the other one stays lit.
Thu Sep 18, 2008 9:34 am
Forum: General Discussion
Topic: Stringed Instrument Tuner, Ideas?
Replies: 30
Views: 7415
Hi again, Little Update here... I tried a 10 percent duty cycle and it seems to help a lot. It appears that the main problem was with a 50 percent duty cycle the eye picked up too much of the vibration and so it became a bit confusing. With only 10 percent the eye only sees a fraction of the string...
Thu Sep 18, 2008 8:49 am
Forum: General Discussion
Topic: Incandescent lamp longevity at half rated voltage
Replies: 18
Views: 5310
Hi there, There might be something to be said about resistance vs Triac phase control vs Diode. ...... whereas the pure resistance method ( two bulbs in series ) would not. This could make a big difference. ------ These three techniques are all different and need to be evaluated separately. Puting ...
Thu Sep 18, 2008 8:18 am
Forum: General Discussion
Topic: Digital television broadcasting frequencies ?
Replies: 10
Views: 3298
Externet wrote:Yes, the FM 3 metre band stays as is. If FM goes full digital will occupy the same band.
Miguel
Thank you.
Mon Sep 15, 2008 10:00 am
Forum: General Discussion
Topic: Digital television broadcasting frequencies ?
Replies: 10
Views: 3298

### Re: Digital television broadcasting frequencies ?

Externet wrote:Hello all
Anyone knows how will the aired RF spectrum look like next year ?

(MHz) --- 30 to 50 stays ? 50 to 88 gone, 88 to 108 stays; 108 to 174 stays, 174 to 220... 220 to 470.... 470 to 900 .... 900+...

Miguel
Thu Dec 20, 2007 6:12 am
Forum: General Discussion
Topic: Merging / splitting DC/AC signals sharing a conductor...
Replies: 16
Views: 5352
Thanks. Did not know the inserters were available commercially. As even the small ones are somewhat bulky for my application, I still prefer to calculate my own. The consumption of the camera is 150mA. The wire gauge of the coil should not drop more than a volt in insertion (~10%). Am fine there. A...
Thu Oct 25, 2007 6:50 am
Forum: General Discussion
Topic: Can I dim a switching power supply?
Replies: 5
Views: 2394
Some "electronic transformers" made for low voltage incandescent lamps (ie 12 V 50 W ) are dimmable (not all of them) An "electronic transformer" is just another name for a switching power supply :grin: If the supply has a fixed duty cycle oscilator it should work, BUT if there is any feedback to re...
Mon Oct 22, 2007 6:03 am
Forum: General Discussion
Topic: Universal motor...
Replies: 5
Views: 2009
Now, 120 VDC is another story! No, at 120VDC it may take too much current and / or overspeed. An universal motor is just a series wound DC motor (that is, the field winding is connected in series with the armature), but it has two small differences: >> As the field winding will have AC, the magneti...
Thu Oct 18, 2007 6:13 am
Forum: General Discussion
Topic: 480VAC Indicator Panel LED
Replies: 22
Views: 7930
Three phase indicator lights are ussually wired in a "Y" configuration (live to neutral) and so they receive only 58% of the line voltage. (58 % = 1/square root of 3 is the relation between "line" and "phase" voltages) In a 480 VAC system the phase voltage would be 277 V. Just wire the three (277V) ...
Tue Oct 16, 2007 6:34 am
Forum: General Discussion
Topic: Automatic voltage selecting transformer
Replies: 7
Views: 2629
You can replace the 110VAC relay with a low voltage DC one, and power it with a regulated supply. It may be something like a 220V/24V transformer, rectifier, filter and 1812 regulator (or, if the relay uses a "low enough" :grin: current, resistor and zenner). With 22V the transformer will output 24V...
Fri Oct 12, 2007 6:13 am
Forum: General Discussion
Topic: 240V transformer on 277V line?
Replies: 17
Views: 5506
As a side note, as the input voltage to a transformer is increased the excitation current increases, causing the copper and the core to heat up more than at lower input voltage. At some point it becomes impractical to use the transformer at that voltage. The current that the transformer takes under...
Tue Sep 25, 2007 6:28 am
Forum: General Discussion
Topic: Amp meter for 1Hp motor
Replies: 12
Views: 3610
The only time I've seen an ammeter permanently mounted on woodworking equipment was on a surface planer where the ammeter indicated if you were taking too large of a bite out of the material being planed. The same machine had a regular magnetic motor starter involved, so had overload protection. I ...
Mon Sep 10, 2007 5:41 am
Forum: Computer Programming
Topic: Protecting PIC inputs?
Replies: 16
Views: 10348
If the input pin can go to +10V then the current may be 10V/1k = 1 mA into a 0V supply or (10V-5V)/1k = 500 microA if the supply goes up to 5V. If tte minmum current used is more than the number of inputs times 500 microA there is no problem. If not, you can add a zenner (perhaps 5.5V or 6V) across ...