Search found 28 matches

by smariotti
Tue Nov 06, 2007 10:42 am
Forum: General Discussion
Topic: Hey Al, try Allied...
Replies: 11
Views: 2508

Yeah, these catalogs are ridiculous. Is there a way to get them to just NOT send them any more? They really should have a checkbox on their online ordering form: [X] Please send me ENORMOUS PHONE BOOK SIZED CATALOG four times a year. that you can uncheck before issuing your order. Or maybe one like:...
by smariotti
Mon Nov 05, 2007 6:57 pm
Forum: General Discussion
Topic: Price too high for four channel AD chip???
Replies: 15
Views: 3239

2 layer boards in Qty 50 should be very cheap per piece. Lots of PCB fabs have online quote calculators so you can do some what-ifs without getting formal quotes. I've never sent anything out to be fabbed, but I look foward to doing so once I'm more confident in my designs. This may be a useful res...
by smariotti
Fri Nov 02, 2007 2:57 pm
Forum: General Discussion
Topic: Problems with Futurlec
Replies: 21
Views: 5488

This is the worst company i have ever dealt with. My first order from them took a long time to come. Longer than I'd have expected, but it did arrive, and it did arrive in toto. My second order from them was a much larger order, and I paid for 3 day shipping and it arrived three days from when they...
by smariotti
Fri Oct 26, 2007 11:41 am
Forum: General Discussion
Topic: Electronics Beginner
Replies: 14
Views: 3095

i mean i collect junk as it is i have several old 3.5 floppy disk drives i can scrap for parts and some old cdroms as well Scrap parts are a great way of pursuing an electronics on the cheap. I pull parts out of a bunch of old salvaged crap all of the time, though doing it requires some soldering /...
by smariotti
Fri Oct 19, 2007 11:07 am
Forum: General Discussion
Topic: Comp USA out of business?
Replies: 16
Views: 3904

SETEC_Astronomy wrote:If it is the case I say goodbye and good riddance. Oh and Comp USA take Radioshack with you.
But without Radio Shack where will I go to pay $2 for a single resistor?
by smariotti
Fri Oct 19, 2007 9:18 am
Forum: General Discussion
Topic: Half-watt resistors in parallel?
Replies: 23
Views: 5889

Well, here's the device. As per normal I'm posting pictures and follow-up to projects I engage in with the help of the N&V/Servo forums crew! http://www.postimage.org/aV1UFZAA.jpg I ended up using four 1.8MOhm 1-watt resistors (I found a great electronics store about 20 minutes north of here that se...
by smariotti
Wed Oct 03, 2007 10:56 am
Forum: General Discussion
Topic: Half-watt resistors in parallel?
Replies: 23
Views: 5889

It's interesting to me that resistors in series are preferred over in parallel. Is this primarily to prevent arcing over the (smaller wattage) resistors? While the voltage IS very high (20kV is likely, on the top end) woiuldn't putting smaller wattage resistors in parallel dissipate current better a...
by smariotti
Tue Oct 02, 2007 2:17 pm
Forum: General Discussion
Topic: Half-watt resistors in parallel?
Replies: 23
Views: 5889

Half-watt resistors in parallel?

I want to discharge a CRT through a 1M Ohm resistor so as not to damage the cascade rectifier that's possibly holding some of the charge. I only have 1/2 watt resistors at 1M Ohm, however, and it's advised to use 3W or higher rated resistors. It would make sense to me intuitively to be able to use s...
by smariotti
Wed Sep 19, 2007 12:04 pm
Forum: General Discussion
Topic: Charging While Wall-Warting
Replies: 45
Views: 8759

The tab on 7805s is the same as the common reference pin, so one on one side of heatsink, and other on other side, shouldn't be a problem. From the schematic, only one 7805 works at a time. I suspect (without doing the math) that if the 3.3V regulator input is moved from 5V to 12V/8.2 (via addition...
by smariotti
Tue Sep 18, 2007 10:11 am
Forum: General Discussion
Topic: Charging While Wall-Warting
Replies: 45
Views: 8759

the cell pack voltage, which is 9.8, which means you would use 9.8 in your charge calculation, not 8.4 volts. 12v - 1.0v for diode - 9.8 for target cell pack charge voltage = 1.2v / 0.050 = 24 ohm resistor, then. I've got a 47 ohm in there from overnight that's charging today. It looks like the cel...
by smariotti
Mon Sep 17, 2007 10:06 am
Forum: General Discussion
Topic: Charging While Wall-Warting
Replies: 45
Views: 8759

I get 16mA charging through 220 Ohms (you forgot to subtract the voltage across the batteries from 12V) :) Cheers, D'oh! I'm getting 48 ohms now. 12v - 1.0fv - 8.4v = 2.5v. 2.5v / 0.050mA = 48 ohms. Your new pack voltage (nominal) is 8.4 volts, but the charge voltage should be calculated first: v=8...
by smariotti
Sun Sep 16, 2007 8:08 pm
Forum: General Discussion
Topic: Charging While Wall-Warting
Replies: 45
Views: 8759

It's too bad you cant use NiMH cells here, as they have a bit more capacity. I'm going to find a place on line that has inexpensive NiMH AA cells (I need to stick with AA because of their size.. I need that thickness for my case) that are rated at 2500mAh-ish. I see AA's for sale on eBay and on som...
by smariotti
Sun Sep 16, 2007 7:48 pm
Forum: General Discussion
Topic: Charging While Wall-Warting
Replies: 45
Views: 8759

If you didn't file, or emory cloth, the battery ends first; and used a BIG soldering iron you probably "cooked" at least one of the cells. I have a flux pen I salvaged from some trash when a neighboring company cleared out of their office space. I can practically make solder stick to teflon with th...
by smariotti
Sun Sep 16, 2007 7:30 pm
Forum: General Discussion
Topic: Charging While Wall-Warting
Replies: 45
Views: 8759

dyarker wrote:"My cells are 700mAh each, with 7 in series for 4900mAh?"

No, with cells in series it is still 700mAH at a higher voltage.
Ahh, Ok. Well, I'd think I'd probably only get an hour's operation if my total charge is never more than 700mAh. :-/
by smariotti
Sat Sep 15, 2007 10:48 pm
Forum: General Discussion
Topic: Charging While Wall-Warting
Replies: 45
Views: 8759

well, the first thing I would try to answer is "what's the current draw of your 3.3 regulator?" Secondly, what's the capacity of your batteries? that should tell you a lot. Now, I hate to say it but your approach is seriously inefficient. Basically, you are using 8.4V to derive 3.3V for an efficien...