Search found 71 matches

by bobsRAC
Tue Jan 28, 2003 2:31 am
Forum: General Discussion
Topic: cheap (and maybe dirty) quadrature oscillator
Replies: 1
Views: 854

Re: cheap (and maybe dirty) quadrature oscillator

You need a clock, 3 inverters, and 2 d-latches.<p>` ` ` ` ` +----o<|---+ ` ` ` ` ` | +-----+ `| ` ` ` ` ` +-|D ` Q|--+---Q0 ` ` ` ` ` ` | ` ` | clock-+-|>o-|> `` | ` ` ` |` ` `+-----+ ` ` ` | ` ` ` | ` ` ` | ` +----o<|---+ ` ` ` | ` | +-----+ `| ` ` ` | ` +-|D ` Q|--+---Q1 ` ` ` | ` ` | ` ` | ` ` ` ...
by bobsRAC
Tue Jan 28, 2003 2:10 am
Forum: General Discussion
Topic: Hello! Newbie to electronics
Replies: 8
Views: 2052

Re: Hello! Newbie to electronics

"The Art of Electronics" is likely the best book on my shelf for discrete circuits, though it's probably not the quick intro you're looking for. Are you looking to get into embedded systems or analog stuff or ???
by bobsRAC
Tue Nov 12, 2002 11:26 am
Forum: General Discussion
Topic: JFET vs BJT
Replies: 4
Views: 1197

Re: JFET vs BJT

Also... here's a fun one...<p>Look up the data-sheet for a JFET and look at the data sheet for a typical N-ch JFET the MPF102 (I've got a link below). Look for Idss and look at the min and max values. You'll notice that the min is 2mA and the max is 20mA. This means that some large percentage of the...
by bobsRAC
Tue Nov 12, 2002 11:10 am
Forum: General Discussion
Topic: JFET vs BJT
Replies: 4
Views: 1197

Re: JFET vs BJT

Another really important design consideration is the tolerance of the manufacturing process. FETS and JFets in particular have very poor manufacturing tolerances, on the order of 10 times worse than BJTs. FETs also have poorer noise characteristics.<p>To get an idea, browse through the data sheets f...
by bobsRAC
Tue Nov 12, 2002 10:52 am
Forum: General Discussion
Topic: Microphones
Replies: 9
Views: 3379

Re: Microphones

Generally, you'll want to use a JFet pre-amp stage to accomodate the very high output impedance of the piezo crystals. There are numerous examples across the web.
by bobsRAC
Tue Nov 12, 2002 10:46 am
Forum: General Discussion
Topic: Microphones
Replies: 9
Views: 3379

Re: Microphones

Piezo-electric mics convert the mechanical energy carred by the sound waves into an electrical energy. Therefore, a volage is generated by the microphone, but the impedance is high (10ish of Meg-ohms I believe). Piezo crystals are used to generate power for roadway flashers in Japan (the yellow ligh...
by bobsRAC
Tue Oct 29, 2002 10:30 pm
Forum: General Discussion
Topic: antenna length
Replies: 5
Views: 2136

Re: antenna length

c = 3x10^8 m/s (300,000,000 m/s)<p>1/4 wave whip antenna<p>length = c/(4*f) meters<p>example:<p>2.4 GHz - (3x10^8)/(4*(2.4x10^9)) = 3.125 cm<p>900 MHz - (3x10^8)/(4*(9x10^8)) = 8.333 cm<p>27 MHz - (3x10^8)/(4*(2.7x10^7)) = 2.778 m
by bobsRAC
Fri Oct 11, 2002 7:02 pm
Forum: General Discussion
Topic: capacitor types
Replies: 19
Views: 5349

Re: capacitor types

I'm from an entirely different school of though. I'm a much newer member of the electronics community than many of our valve-lovers, and therefore I am focused on modular and digital techniques.<p>The most appealing approach to me is a clean amp (having characteristics approaching ideal) and adding ...
by bobsRAC
Thu Oct 10, 2002 10:00 am
Forum: General Discussion
Topic: PIC/Stamp Microcontroler Where to Start
Replies: 9
Views: 2025

Re: PIC/Stamp Microcontroler Where to Start

I started out with Microchip's PicStart programmer, and it works rather well for assembly projects. I've done a fair amount of programming (20 or 30 projects each) in c and assembly on the PIC, and have found that Microchip's dev tools are somewhat unstable at times and that the chips aren't as powe...
by bobsRAC
Thu Oct 10, 2002 9:37 am
Forum: General Discussion
Topic: Relay for water cool system
Replies: 4
Views: 1071

Re: Relay for water cool system

You could build a board with a microController to PWM some SCRs. This would allow the board to vary the power without dissipating a plethora of heat.
by bobsRAC
Thu Oct 10, 2002 9:25 am
Forum: General Discussion
Topic: Voice Recognition
Replies: 8
Views: 1378

Re: Voice Recognition

I'm believe that most of the successful voice recognition software uses a time-domain analysis.<p>For an example of a cheap boars that recognizes a few commands, goto...<p>SensoryInc.com
by bobsRAC
Sat Oct 05, 2002 10:51 pm
Forum: General Discussion
Topic: diode
Replies: 19
Views: 3161

Re: diode

Tunnel diodes have a operating region in which the device exhibits a negative resistance.<p>The first radio transmitters were operated without the use of a three terminal device. The US military even used 1 MegaWatt transmitters before the invention of the vacuum tube. This was made possible by the ...
by bobsRAC
Tue Sep 24, 2002 7:37 pm
Forum: General Discussion
Topic: New style 3rd brake light
Replies: 4
Views: 972

Re: New style 3rd brake light

Just to throw it in there... MOSFET switches are cheaper and more effective than big BJTs for simple on-off, low-speed switching.<p>As an example, for $2.52 in quantities of (1), the IRF1404 from International Rectifier has an on resistance of 0.007 Ohms max at 160dC. Therefore, at 100A, there is a ...
by bobsRAC
Sun Sep 08, 2002 11:15 pm
Forum: General Discussion
Topic: Defining a cathode
Replies: 7
Views: 1811

Re: Defining a cathode

Jeeves told me:<p> cathode 1 : the electrode of an electrochemical cell at which reduction occurs: a : the negative terminal of an electrolytic cell b : the positive terminal of a galvanic cell<p> IversonSoftware.com told me:<p> Electrolytic cell , an apparatus in which chemical change is caused to ...
by bobsRAC
Sun Aug 25, 2002 11:03 am
Forum: General Discussion
Topic: Switch debouncing
Replies: 9
Views: 1615

Re: Switch debouncing

the lowpass filter is proned to making the problem worse... The lowpass makes the signal rise and fall more slowly, keeping the signal around the switching point for a longer period. any spike or noise that occurs around this region can cause another trigger.<p>The simplest scheme is a pair of inver...