Project for interested 10 yr old

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terri
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Re: Project for interested 10 yr old

Post by terri » Mon Dec 06, 2004 10:13 pm

Used to be that all the transistor manuals and tube manuals had full-blown circuits in the backs of the books showing their products' applications. I built a hi-fi mono amp using 6V6's for finals from one of the old RCA tube manuals (ca 1952 or so) and a couple of other things from these sources.<p>I acquired a HW-8 HF Code rig which someone had built from the kit and could not get it to work, and I had to re-vamp the whole thing.... sloppy wiring, poor soldering... the usual. Got it put together right and it turned out to be a neat little qrp code rig, after I busted the hum out of the power supply.<p>One hint: whatever you decide on, make sure you will be able to help out with the diagnostics if it doesn't work on first power-up.
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Re: Project for interested 10 yr old

Post by Mike6158 » Tue Dec 07, 2004 4:24 am

Mike-<p>Your site has good info on it and you aren't "selling" anything so I don't know why anyone would mind if you mention it in posts that you make. I'm a newb here but I don't... Besides... I get the feeling that the gentlemen that have been here awhile won't hesitate to tell you if they mind :D
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Re: Project for interested 10 yr old

Post by John Paul » Tue Dec 07, 2004 5:39 pm


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Re: Project for interested 10 yr old

Post by philba » Thu Dec 09, 2004 8:12 pm

I took a slightly different tack for my 9 year-old (last year, he's 10 now). I got him a minisumo markIII robot but I assembled the controller board, mod'd the servos and wrote an initial program for him. He build the rest of it with some guidance from me. It was a good experience working together on it. <p>It was a great way to get him thinking about how to go beyond the basic kit (better traction, smarter program, more power). He's pretty proud of it.<p>It's a really great price for a mini sumo robot kit. It can also do line following and there are lots of cool additional things you can do with it.<p>http://www.junun.org/MarkIII/Info.jsp?item=1

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CeaSaR
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Re: Project for interested 10 yr old

Post by CeaSaR » Sat Dec 11, 2004 7:23 pm

OK, here's the scoop. I looked through my junk "pile" and came up with several Jim-Paks of 2n3904/06's, tons of resistors (mostly 1/4 watt, various values), many electrolytic and ceramic caps (also various values and voltages). Looked in Radicle Slack and found that the single most prevalent transistor is a TO-92 2n2222 (15 for $2.95). All others are either in the 1 count range or are horribly overpriced. Oh, I also have a 9v 800ma dc wallwart to throw in the mix.<p>Now, does anyone have a schematic to use the 2n3904/06 combo to drive the 2n2222(s) as a transformerless audio amplifier (4-8 ohm output)using 9 volts? Or maybe some help using one of the previously referenced schematics as a base and modifying to use said combo? <p>Thanks in advance.<p>CeaSaR
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philba
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Re: Project for interested 10 yr old

Post by philba » Sat Dec 11, 2004 8:32 pm

check out discover's audio amp section. I noticed several transistor based amp circuits. Also, I wouldn't fixate on circuits that only show 3904/06s and 2222s. These are general purpose transistors so you could substitute them for most other general purpose transistors. http://www.discovercircuits.com/A/a-audioamp.htm<p>Also, you can get the parts a lot cheaper than radio shack. Goldmine and All have them much cheaper. My favorite, Glitchbuster has them really cheap (12/$.98) with really cheap shipping and fast turn around. You just need to use paypal. http://www.glitchbuster.com/ I have no relationship with him other than as a satisifed customer.

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CeaSaR
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Re: Project for interested 10 yr old

Post by CeaSaR » Sun Dec 12, 2004 8:34 pm

Paul,
I like what Qkits has there - I just wish they published the schematic they reference. Circuit: complimentary pair feeding an emitter follower - output at the emitter... Hmmm, an idea is fomenting...<p>Philba,
Great link! Got a few pages printed out. I know RS is more expensive than most anywhere, but I want to be able to surprise him - he normally looks at the mail before I do and would wonder what was being delivered.<p>Still working on it...
CeaSaR<p>Oh, and Mike,
Don't feel bad about trying to help. That's what we are here for - help, in one way or another :) As long as the link is relevant (yours is) then there should be no problem. Thanks.<p>[ December 12, 2004: Message edited by: CeaSaR. ]</p>
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CeaSaR
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Re: Project for interested 10 yr old

Post by CeaSaR » Tue Dec 14, 2004 7:29 pm

I believe I found the schematic for the Qkits project here,only it's a KitsRus.com PDF on www . electronics123 . com! Go figure.<p>Looking over all the info I've come across (thanks to all who have pointed the way!), I have realized that what I am actually looking for is a quasi-complementary topology. You know, using the PNP/NPN pair to drive higher power NPN's on either side of the rail. Do I have that right? It's been , oh , probably 10 or so years since I've read my "big book of electronics" that is hidden somewhere up in the dark recesses of atticdom. Any help/hints/pictures/schematics/true stories/blatant lies etc... :D <p>Thanks again everyone.
CeaSaR<p>Hey, if you are looking for some old amp schematics check this out: http://www.hilberink.nl/amps/amps.htm<p>[ December 14, 2004: Message edited by: CeaSaR. ]</p>
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CeaSaR
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Re: Project for interested 10 yr old

Post by CeaSaR » Tue Dec 14, 2004 7:53 pm

OK, I started a search and found Len's PSPICE Circuit Attic. His first PDF has a schematic I might just be able to scale for my requirements. Does anyone have any suggestions about what might need to be changed for 9-12 volt operation and using 2n2222's for the outputs? I would appreciate any help. Also, what do you think the output power might be at max 12v, 1 amp?<p>Thanks again.
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rshayes
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Re: Project for interested 10 yr old

Post by rshayes » Tue Dec 14, 2004 11:04 pm

Real 2N2222 transistorss are in a metal TO-18 case. They can probably dissipate about 100 milliwatts. Yes, I know the data sheets give a rating of 300 milliwatts dissipation in free air. What the data sheets fail to mention is that the case is over 100 degrees centigrade (ie, boiling water) under this condition. Adding a heat sink would help to some extent.<p>The efficiency of a class B output stage delivering a maximum amplitude sine wave is at best about 67 percent. Output power with two transistors would be less than 400 milliwatts at best. Think of driving headphones rather than speakers.<p>A 12 volt supply would probably allow a peak output voltage of about 10 volts peak to peak. This would be about 3.5 volts RMS. An output power of 300 milliwatts would be delivered into a load of about 40 ohms. The peak current would be about 88 milliamps, which can probably be handled by 2N2222's.<p>Connecting two 8 ohm elements in series (the two sides of a stereo earphone) would give a load impedance of 16 ohms. Delivering 300 milliwatts into this load would require about 6.2 volts peak to peak. This would imply a supply in the 8 volt range, probably a 9 volt battery. The peak current would be about 193 milliamps, which might require paralleling two 2N2222's. This still might be a reasonable project.

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Re: Project for interested 10 yr old

Post by peter-f » Wed Dec 15, 2004 3:04 am

stumbled into htis site today--
may help with some kits... many parts.<p>http://www.circuitspecialists.com/level.itml/icOid/192<p>Hoping we're still on time!

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CeaSaR
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Re: Project for interested 10 yr old

Post by CeaSaR » Wed Dec 15, 2004 10:31 am

The 2n2222's that I looked at had ratings of 60v and 800ma, that's why I thought of using them. Not sure if they had any suffix or not. Plus, they come in a 15 pack, so if something happens they can be changed without a trip to the store. I'll have to look again to make sure what I read. You know how well the help at RS keeps their stock organized (It goes in that drawer there somewhere. OK, that's close enough... :roll: ). Maybe I ought to stick with the 2n3055's, but only singles. They ought to run cool enough without heatsinks on 12v 1amp. BTW, the input will more than likely be from the headphone jack of a CD player. Should I add a preamp stage?<p>Thanks again.<p>CeaSaR
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Edd
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Re: Project for interested 10 yr old

Post by Edd » Wed Dec 15, 2004 11:17 am

Your initial reference to 2222 based outputs tended to sway towards a higher output power level a bit later….also most of the supplied schematic references tended to utilize heftier TO-220 cased units being utilized for the output discretes.
In lieu of using the TO-18 cased 2N2222/2N2907 pair an intermediate quantum jump in power could be obtained with their big brother counterparts TO-5 encased 2N2221/2N2905 pairs.
Also,how about looking at Sir Charles site and see if any of his circuits might be usable in your application.<p>http://www.techlib.com/electronics/audi ... transistor <p>Hail CeaSaR!....hi....hi<p>73's de Edd
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Re: Project for interested 10 yr old

Post by rshayes » Wed Dec 15, 2004 2:43 pm

The maximum current rating of the 2N2222 is given as 800 milliamps on the data sheet. This is probably based on a defined drop in current gain compared to its peak value. This isn't a very practical number.<p>The data sheet specifies minimum current gains at several points. The current gain at 10 milliamp is indicated as a DC measurement. Current gains at higher currents (such as 150 milliamps) are measured under pulsed conditions (300 microsecond, 2% duty cycle).<p>The collector-base voltage is given as 60 volts. The collector-emitter voltage is 30 volts. In most circuits, the collector-emitter voltage is the applicable rating. The collector-base voltage rating might apply in special circumstances, such as a cascode circuit.<p>The free air dissipation rating is 500 milliwatts. This is derated to zero at 175 degrees degrees (3.33 milliwats per degree centigrade). The case temperature rating is 1.8 watts. This is derated to zero at 175 degrees centigrade (12 milliwatts per degree centigrade). When the transistor is dissipating 500 milliwatts in free air at 25 degrees centigrade, the junction temperature will be 175 degrees. The junction to case temperature drop will be about 42 degrees, leaving the case at 133 degrees centigrade (271.4 degrees farenheit).

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