Temp. circuit on page 66 of July N&V

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Mike
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Temp. circuit on page 66 of July N&V

Post by Mike » Sun Jun 27, 2004 3:33 am

I want to build this circuit, but want it to trigger a relay. Can I do this directly from the output? If so, would all I need to do is connect the relay between output and ground?<p>What I want it to do is trigger at a certain temperature and turn off when its below it. The relay is connected to a fan.

hp
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Re: Temp. circuit on page 66 of July N&V

Post by hp » Sun Jun 27, 2004 6:23 pm

Since the LM339 is a logic level output chip, all you would need is to stick a transistor and resistor on the output of the opamp. I would use a general purpose NPN (such as the 2N3904) and a 10k resistor on the base. Make sure you stick a diode on the relay coil so the kickback won't kill your transistor.<p>Harrison

Mike
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Re: Temp. circuit on page 66 of July N&V

Post by Mike » Mon Jun 28, 2004 4:55 am

so the base of the transistor connects through a 10K resistor to the output of the lm339, then where do the collector and emitter go? I would assume the emitter goes to the relay, but what about the collector? Finally, about the relay, does it connect between the transistor and ground? And the diode connects across the two coil termanals, right?

hp
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Re: Temp. circuit on page 66 of July N&V

Post by hp » Mon Jun 28, 2004 7:20 am

Take a look at this schematic:<p>Image<p>Harrison<p>[ June 28, 2004: Message edited by: hp ]</p>

perfectbite
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Re: Temp. circuit on page 66 of July N&V

Post by perfectbite » Mon Jun 28, 2004 9:44 am

I am having trouble visualizing what happens when a coil field collapses. My understanding is that the electrons go 'shooting off 'en masse but my understanding is also that an equal number of 'holes' are created. How are these holes filled? Does the diode direct them, in their mad rush, back to fill their own vacated 'holes' or does it stop them in their tracks?<p>If there were absolute synergy between electrons and their holes there could be Voltage (EMF) but there wouldn't be any Amperage because the electrons wouldn't be able to leave their orbits so imbalances between moving electrons and their vacated voids must exist.<p>Without the diode, when the electrons went to ground, in this case smoking the transistor along the way, what stress (if any) would that put on the positive source (or does it have 'holes' in abundance waiting for such an opportunity) and how would replenishing such a large number of holes transiently affect both the power supply and the circuit's values?<p>[ June 28, 2004: Message edited by: perfectbite ]</p>

Tommy volts
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Re: Temp. circuit on page 66 of July N&V

Post by Tommy volts » Mon Jun 28, 2004 12:27 pm

HP,<p>That is a nice schematic. How did you get it on your post?<p>I think you must have put the drawing on a website and then posted it as a URL with a UBB code? <p>Ive tried to paste in schematics directly but have never been able to do it.

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haklesup
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Re: Temp. circuit on page 66 of July N&V

Post by haklesup » Mon Jun 28, 2004 12:53 pm

Forget about holes and electrons, they apply mainly to semiconductor components. If electrons "went flying off" you would either see a corona (plasma) or be able to detect a radio pop.<p>In a coil, when the power is switched off the magnetic field lines (which loop around the coil from pole to pole) rapidly shrink to zero. as the field lined pass through the coil windings (as they disappear) they cause a voltage to appear across the terminals of the coil. This transient voltage has the opposite polarity as the voltage used to energize the coil in the first place. Its magnitude is effected by the components attached but can be as high as the supply V in the opposite direction. This is generally not a problem for the coil or supply but it can damage the semiconductor components around it.<p>Note that in the schematic the diode is reverse biased to the supply which means it will be forward biased during the transient pulse. This limits the magnitude of the V pulse to the voltage drop across the diode (about half a volt)

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Re: Temp. circuit on page 66 of July N&V

Post by Ron H » Tue Jun 29, 2004 7:15 pm

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by haklesup:
Forget about holes and electrons, they apply mainly to semiconductor components. If electrons "went flying off" you would either see a corona (plasma) or be able to detect a radio pop.<p>In a coil, when the power is switched off the magnetic field lines (which loop around the coil from pole to pole) rapidly shrink to zero. as the field lined pass through the coil windings (as they disappear) they cause a voltage to appear across the terminals of the coil. This transient voltage has the opposite polarity as the voltage used to energize the coil in the first place. Its magnitude is effected by the components attached but can be as high as the supply V in the opposite direction. This is generally not a problem for the coil or supply but it can damage the semiconductor components around it.<p>Note that in the schematic the diode is reverse biased to the supply which means it will be forward biased during the transient pulse. This limits the magnitude of the V pulse to the voltage drop across the diode (about half a volt)<hr></blockquote><p>The magnitude can be much higher than the supply voltage in the opposite direction. <p>V=L*di/dt<p>Meaning that the voltage is equal to the inductance times the rate of change of current.<p>In the absence of low shunt impedance (capacitance, diode,etc.), di/dt can be very high, leading to hundreds or even thousands of volts. This is what causes arcing between switch contacts in the absence of snubber networks.

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Re: Temp. circuit on page 66 of July N&V

Post by perfectbite » Wed Jun 30, 2004 9:13 pm

Thank you Haklesup and Ron H. I've reached the edge of calculus in electric theory, Phew! And understood it's significance. Double Phew! <p>Mike, I'm glad you got the answer with the schematic so that I could ask another of my dumb, some would say inane, questions. Thank you for asking the question.<p>Just in case you weren't aware, July 2004's Scientific American, which hasn't had the amateur scientist for a very long time now, has an article on EMR (extraordinary magnetoresistance) which I think you would find interesting. That is if you don't already know about it. (Worth buying the issue for? I don't know)

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Re: Temp. circuit on page 66 of July N&V

Post by Mike » Thu Jul 01, 2004 5:31 pm

Wow, i never expected a relay's operation to be so complicated. I'll let everybody know how this turns out (when i get around to it)

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Edd
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Re: Temp. circuit on page 66 of July N&V

Post by Edd » Thu Jul 01, 2004 6:53 pm

Tommy der Voltster:<p>Well, looking at “hp’s” post , seems this might approximate the situation: First he prepared a schematic GIF for Mike/you meeting your requested needs and since he would want it available for you /others 24/7 he mirror hosted it to a “fwd” web site. In these hereabouts fwd would be indicative of Ft Worth/Dallas but in his case, we can suspect FriendsWooD, Tex.
Unless your computer being used is an old kluge, get on the web page with that hp post page showing. Look up at the top and L-click on View and then drop down to Source and L-click and then the web page HTML encoding should show up on a notepad. Take note, that would be the case, if the amount of text encompassed was within the set parameters selected at the source, in this case, this string of posts has become so long that you might need to go to the condensed text that is normally presented at the bottom of the page when you make a “Reply to this post” entry. So go ahead and make that request to add to the post…..which you will actually not do…..but that will get the condensed info on screen for you. So again, look up at the top and L-click on View and then drop down to Source and L-click and then the web page HTML encoding should show up on a notepad. At this posting time the string is just on the borderline of length so you may not have to do the second procedure. Any case, I have covered U in either situation.
Top corner click to max its size and then select some non repetitive/distinct text within the text of the message in the particular text area of interest. E.G. let’s take “at this schematic:” which was the very last wording before the schematics appearance. So now you hold control and hit “F” and the dialog box for an info search should pop up and then you put in the prior info agreed upon above. Then Left click on Find next, trying both down/and/or/ up and the scrolling should zip down to the worded area of interest.and highlight those words.
I excerpted this snippet from around the area of interest:
Take a look at this schematic:<p><img src="http://mirror.fwdweb.com/misc/images/re ... Harrison<p>[ June 28, 2004: Message edited by: hp ]</p>
</FONT>
so…..you can see his reference to this above which I have further excerpted and made active for you to click on…….
http://mirror.fwdweb.com/misc/images/relayschem.gif
bam …!!! .see…. that goes to his schematic "image source".<p>I would have to consult my archives , but there are a few circuit sites that store their individual GIF schematics separate from their text and that can be accessed and just the schematics lifted and placed as pictoral references in further posts.
Also, oftimes I go into HTML Web structuring and extract forms, borders, outlining, shadowboxing and other initially time consuming creations that I can merely lift with a cut 'n paste and then slightly HTML modify them in their structuring or colorization to meet my final needs/desires.<p>73's de Edd
[email protected] .........(Interstellar~~~~Warp~~~Speed)
[email protected].........(Firewalled-Spam*Cookies*Crumbs)
;) :p<p>[ July 01, 2004: Message edited by: Edd Whatley ]</p>

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Re: Temp. circuit on page 66 of July N&V

Post by dyarker » Thu Jul 01, 2004 9:02 pm

Tommy volts,<p>Short answer to "I think you must have put the drawing on a website and then posted it as a URL with a UBB code?" is yes. Images are not uploaded to Nuts & Volts' server when you click "Add Reply".<p>Edd,<p>For images (.gif, .jpg, .png, etc) try putting mouse cursor over the image, right click, left click "Save Picture As...". For background images, javascript (.js) and style (.css) files linked in the < h e a d >, and the other items you mentioned, the long method you described is needed.
Dale Y

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