Search found 82 matches

by jimmy101
Sun Apr 03, 2011 1:02 pm
Forum: General Discussion
Topic: GEIGER MULLER TUBES, WHERE DO I FIND ONE THESE DAY
Replies: 5
Views: 2157

Re: GEIGER MULLER TUBES, WHERE DO I FIND ONE THESE

Electronics Goldmine has several tubes and counters. You can also check Ebay for surplus CV (Civil Defense) counters, e.g., CDV-700. Up until recently a working one could be had for about $50. Since the events in Japan I suspect the prices have probably tripled. Ebay often also has (or used to have)...
by jimmy101
Sat Mar 12, 2011 11:51 am
Forum: General Discussion
Topic: Thermocouple Switching
Replies: 15
Views: 4207

Re: Thermocouple Switching

Actually though, the voltages are not generated across junctions, the voltages are generated across the lengths of wire. Actually, the electromotive force (EMF) is generated across and by the junction. Therefore the voltage is across the junction, not the wire. There is only a voltage across the wi...
by jimmy101
Sun Feb 20, 2011 9:36 am
Forum: General Discussion
Topic: Physics Puzzle
Replies: 16
Views: 3825

Re: Physics Puzzle

Dang, multiple cases of confudling "whole" with "hole"!
by jimmy101
Sun Feb 20, 2011 9:35 am
Forum: General Discussion
Topic: Physics Puzzle
Replies: 16
Views: 3825

Re: Physics Puzzle

As a starting point for calculating the impedance of a hole in air this particular example is actually trying to calculate the "resistance" of the hole. The impedance of the whole won't be the same. The impedance of a hole can be darn near infinity even for cases where the resistance of the whole is...
by jimmy101
Sat Feb 19, 2011 12:07 pm
Forum: General Discussion
Topic: Physics Puzzle
Replies: 16
Views: 3825

Re: Physics Puzzle

The velocity of the air is not constant so question #2 doesn't make any sense. The pressure in the box as given is the gauge pressure and not the absolute pressure. The absolute pressure would be assumed to be 1 ATM + the 1kg/m^2. Since the air stays in the box the actual pressure in the box is 1 AT...
by jimmy101
Thu Jan 20, 2011 10:01 am
Forum: General Discussion
Topic: Thermocouple Switching
Replies: 15
Views: 4207

Re: Thermocouple Switching

If you are doing logic switching I would think you might as well use an analog mux/demux instead of a relay. Use a pair of MUXs, one for the reading thermocouples and another for the cold junctions. That should largely cancel any EMFs generated by the wire junctions.
by jimmy101
Mon Jan 10, 2011 10:35 am
Forum: General Discussion
Topic: Question about relays..
Replies: 9
Views: 2212

Re: Question about relays..

Are there incandescent bulbs in the strings? If there are, the startup current will be much higher than the rating of the string. IIRC, the resistance of an incandescent bulb can swing by a factor of 10. For example, a typical 100 watt 120V light bulb is about 10~20 ohms at room temperature but ~150...
by jimmy101
Fri Sep 17, 2010 3:18 pm
Forum: General Discussion
Topic: Can anyone define a 14 pin DIP NS 20968L1?
Replies: 3
Views: 1004

Re: Can anyone define a 14 pin DIP NS 20968L1?

"20968" comes up on DigiKey as "PCA9546APWR 296-20968-1-ND 4-Channel I2C and SMBus Switch". Actually, there are a couple, all appear to be of the same function (4 channel I2C bus switches.)

No idea if that is actually what you have.
by jimmy101
Sat Aug 28, 2010 11:24 am
Forum: General Discussion
Topic: Help to build a Ion Detector, please....
Replies: 7
Views: 3504

Re: Help to build a Ion Detector, please....

http://www.techlib.com/science/ion.html http://www.sciencebuddies.org/science-fair-projects/project_ideas/Elec_p064.shtml If you want a Geiger Counter type setup then check Ebay. You can usually find simple (cheap) Russian made counters that use a tiny Geiger-Muller tube for about $20. You can also ...
by jimmy101
Thu Aug 26, 2010 2:53 pm
Forum: General Discussion
Topic: Infrared detector Pen.
Replies: 2
Views: 954

Re: Infrared detector Pen.

Or, just point the remote at a digital camera. The camera has no problem seeing the IR of the remote. Or, connect just about any solid state light detector (phototransistor, photodiode...) across the mic input of a PC or laptop (maybe with a 1K-10K series resistor), fire up your favorite audio recor...
by jimmy101
Tue Jul 20, 2010 4:11 pm
Forum: General Discussion
Topic: CELL PHONE BLOCK
Replies: 17
Views: 4158

Re: CELL PHONE BLOCK

All true, a good faraday cage is a lot of work. But, steel framed buildings are often enough to severely inhibit cell phone signals. A bit of shielding might be enough.
by jimmy101
Mon Jul 19, 2010 5:32 pm
Forum: General Discussion
Topic: Need accurate temperature display
Replies: 17
Views: 3374

Re: Need accurate temperature display

One more thing (ya, there is always at least one more thing...) Are you sure there isn't something confudling the thermostat? It might be working correctly for the cubic foot or so of house around the thermostat but that might be a poor representation of the rest of the house. Sun on the thermostat ...
by jimmy101
Mon Jul 19, 2010 5:25 pm
Forum: General Discussion
Topic: Connector Identification
Replies: 5
Views: 1304

Re: Connector Identification

Another possibility is to just measure the diameter (or length + width) of the individual pins. You can then buy bare matching receptacles form Mouser, Digikey etc. and make up your own cable without any shell at all. To keep the pins from shorting together install them into the connector on the boa...
by jimmy101
Mon Jul 19, 2010 5:21 pm
Forum: General Discussion
Topic: CELL PHONE BLOCK
Replies: 17
Views: 4158

Re: CELL PHONE BLOCK

If you want to keep it legal, and not risk the legal ramifications of broadcasting, or blocking other signals, or interfering with someone's pacemaker :shock: ... A Faraday cage greatly attenuates radio waves. If you have a building with foil faced insulation and that insulation happened to be groun...
by jimmy101
Sun Jul 18, 2010 10:51 am
Forum: General Discussion
Topic: Need accurate temperature display
Replies: 17
Views: 3374

Re: Need accurate temperature display

I don't even want to think about what Reloadron's set of thermometers is worth. Heck, the last research chemistry lab I worked in we removed all the mercury containing thermometers and replaced them with digital ones. (Spilled mercury is just to dangerous and to much of a PITA to clean up.) I really...