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       <title>CircuitDB News</title>
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       <description>Free electronics circuits &amp; schematics!</description>
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          <item>
             <title>LM35 termometer</title>
             <link>http://www.CircuitDB.com/circuits/id/268</link>
             <pubDate>Fri, 18 Jul 2008 16:05:53 +0200</pubDate>
             <guid><guid>http://www.CircuitDB.com/circuits/id/268</guid></guid>
             <description><![CDATA[an adjustment termometer by LM35
this file simulated by Proteus 7.2 and micro program is on Bascom]]></description>
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          <item>
             <title>Universal Ding-Dong</title>
             <link>http://www.CircuitDB.com/circuits/id/267</link>
             <pubDate>Fri, 23 May 2008 07:42:20 +0200</pubDate>
             <guid><guid>http://www.CircuitDB.com/circuits/id/267</guid></guid>
             <description><![CDATA[One frequently finds gongs or chimes for sale in antique shops or Eastern markets.  But supposing one would want to wire these to a pushbutton at the front door to create a ding-dong doorbell?  How would this be done?  Or consider, for a moment, more creative possibilities.  How would one e.g. cause wine-glasses or African drums to resonate when a doorbell is pressed?

The circuit shown in Fig. 1 provides a mechanical means of striking two gongs or chimes in sequence -- one when the doorbell is pressed, the other when it is released.  This it does by briefly activating two solenoids in succession -- or even two motors to which suitable hammers are attached. It is a circuit which was rejected by a publisher, for the reason that it was thought to be too complex -- which really it is.  I had been designing various embodiments of the same idea, and this embodiment was not the most elegant.  Having said this, it works perfectly well.

The circuit is unusual from the point of view that it is based on two pulse shorteners, IC1a and IC1b.  These are essentially two monostable timers with special arrangements at their inputs.  Of critical importance, in these circuits, is that the potential between S1 and R1 should change fairly rapidly when S1 is pressed, and that the trigger inputs of IC1a and IC1b should be suitably biased. 

C2 serves to debounce pushbutton switch S1 – however, its value cannot be too high, due to the requirements of the pulse shortener circuit.  TR1 and R2 serve as an inverter.  IC1a is effectively a negative-edge-triggered monostable timer, so that when pushbutton switch S1 is pressed, IC1a's output goes “high”, TR2 conducts, and solenoid SOL1 is activated.  D1 suppresses back-EMF, which could potentially destroy the IC. 

When pushbutton S1 is released, C2 rapidly discharges through R1.  IC1b is effectively a positive-edge-triggered monostable timer, so that when IC1b's output goes &quot;high&quot;, TR3 conducts, activating solenoid SOL2.  D2 is again provided to suppress back-EMF.  R9 and R10 are not strictly necessary in the circuit, but limit damage in the unlikely event of the failure of TR2 or TR3.

Unless a large battery is used for B1, C1 is needed to provide the &quot;whack&quot; required for solenoids SOL1 and SOL2.  If the pulses which activate SOL1 and SOL2 seem to be too long or too short (they are less than a tenth of a second each as shown), the values of R7 and C5, respectively R8 and C6, may be adjusted according to the formula t = 1.1 R C seconds.  TR1 is a miniature MOSFET.  If an equivalent is required, it may be replaced with the same MOSFET as is used for TR2 and TR3.  If TR2 and TR3 are not to be found, rough equivalents may be used, on condition that their gate voltage is at least a quarter below the supply voltage. 

Ideally, solenoids SOL1 and SOL2 would be 12V push-action types, or pull-action types which have a thrust pin at the back.  However, plain pull-action types should work if they are touching the chimes or gongs when the circuit is at rest (they would then pull back, bounce, and strike).  Small DC motors may be used with hammers attached, with suitable series resistors if required.  These would likely need longer timing periods for monostable timers IC1a and IC1b.

The circuit may use the (original) bipolar version of the 555 timer IC, or its more recent CMOS equivalents.  If a CMOS equivalent is used, standby current is likely to be below 2mA.  That is, an AA alkaline battery pack would last about two months on standby.  For longer periods, a regulated power supply is recommended.  The supply voltage will ideally be 12V, but may be reduced to 9V. 

Copyright Rev. Thomas Scarborough
[Contact the author of this article at scarboro@iafrica.com]]]></description>
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          <item>
             <title>Fonera patch  version 0.2 released</title>
             <link>http://www.CircuitDB.com</link>
             <pubDate>Thu, 08 May 2008 16:09:06 +0200</pubDate>
             <guid><guid isPermaLink="false">news 20 at CircuiDB.com</guid></guid>
             <description><![CDATA[Today we released a new patch for the Fon firmware. We have included OpenVPN in the firmware so your Fonera can now act as an VPN server! <a href="http://www.circuitdb.com/articles/11/5" target="_blank" class="postlink">Download and read more here</a>.]]></description>
          </item>
          <item>
             <title>Tone Control Circuit</title>
             <link>http://www.CircuitDB.com/circuits/id/266</link>
             <pubDate>Sun, 04 May 2008 05:25:46 +0200</pubDate>
             <guid><guid>http://www.CircuitDB.com/circuits/id/266</guid></guid>
             <description><![CDATA[Based on the classic Baxendall tone control circuit, this provides a maximum cut and boost of around 10dB at 10K and 50Hz.
The first [url=http://www.chinaicmart.com/suppliers/174/BC109C.html]BC109C[/url] transistor (left hand side) is acting as a buffer. It provides the circuit with a high input impedance, around 250k has a voltage gain of slightly less than unity. As the Baxendall tone control circuit is a passive design, all audio frequencies are attenuated. The position of the controls and reactance of the capacitors alters the audio response. The last transistor provides a slight boost of about 3x. The output is designed to feed an amplifier with input impedance of 10k to 250k. Both tone controls should be linear type potentiometers.]]></description>
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          <item>
             <title>3 seconds to 2 minutes timer</title>
             <link>http://www.CircuitDB.com/circuits/id/265</link>
             <pubDate>Tue, 22 Apr 2008 08:33:02 +0200</pubDate>
             <guid><guid>http://www.CircuitDB.com/circuits/id/265</guid></guid>
             <description><![CDATA[This timer makes a LED be on for a certain amount of time after pressing the switch.
This time is adjustable from 3 seconds to 2 minutes using the potmeter.
Instead of a LED other load can be connected to this circuit, a relay for instance.

[url=http://www.circuitdb.com/download.php?fileID=217]TinyCAD file of this circuit[/url]]]></description>
          </item>
          <item>
             <title>Fun with La Fonera</title>
             <link>http://www.CircuitDB.com/articles/11</link>
             <pubDate>Mon, 21 Apr 2008 23:03:18 +0200</pubDate>
             <guid><guid>http://www.CircuitDB.com/articles/11</guid></guid>
             <description><![CDATA[Building a serial port interface. Mount network shares. Build your own modifed firmware for La Fonera while keeping the original Fonera functionality. ]]></description>
          </item>
          <item>
             <title>And the winner is.....</title>
             <link>http://www.CircuitDB.com</link>
             <pubDate>Mon, 31 Mar 2008 13:12:53 +0200</pubDate>
             <guid><guid isPermaLink="false">news 19 at CircuiDB.com</guid></guid>
             <description><![CDATA[CircuitDB is proud to announce that <a href="http://www.circuitdb.com/profile.php?mode=viewprofile&u=369" target="_blank" class="postlink">saurabhparashar</a> is the winner of the <a href="http://www.circuitdb.com/contest/" target="_blank" class="postlink">CircuitDB Design Contest 2008!</a> He sent in his <a href="http://www.circuitdb.com/circuits/id/234" target="_blank" class="postlink">Programmable path navigator Robot project</a>. Congratulations saurabhparashar! You win 100 US dollar and eternal fame!]]></description>
          </item>
          <item>
             <title>New WiiKey firmware (1.9S) available</title>
             <link>http://www.CircuitDB.com</link>
             <pubDate>Wed, 26 Mar 2008 23:46:49 +0100</pubDate>
             <guid><guid isPermaLink="false">news 18 at CircuiDB.com</guid></guid>
             <description><![CDATA[Here is some good news for WiiKey owners, <a href="http://wiikey.cn" target="_blank" class="postlink">http://wiikey.cn</a> is up again! They also have released an update that should fix the problem with original Super Smash Bros Brawl disc and add a DVD update blocker to prevent a NTSC disc to ruin your PAL Wii.


Just to be sure CircuitDB will continue hosting the files <a href="http://www.circuitdb.com/articles/8" target="_blank" class="postlink">here</a>.]]></description>
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             <title>Quick Draw</title>
             <link>http://www.CircuitDB.com/circuits/id/264</link>
             <pubDate>Thu, 28 Feb 2008 12:51:31 +0100</pubDate>
             <guid><guid>http://www.CircuitDB.com/circuits/id/264</guid></guid>
             <description><![CDATA[The object of Quick Draw is to test your reaction time against your opponent's. A third person acts as a referee and begins the duel by pressing S1, which lights LED1. Upon seeing LED1 go on, you try to outdraw your opponent by moving S2 from &quot;Holster&quot; position to &quot;Draw&quot; position before your opponent moves S3 from &quot;Holster&quot; to &quot;Draw&quot; position. Who ever gets there first will light the corresponding LED and will automatically prevent the other LED from lighting, clearly indicating a winner.

Copyright 2001 [url=http://home.maine.rr.com/randylinscott/index.html]Randy Linscott[/url]]]></description>
          </item>
          <item>
             <title>Touch 'N Flip</title>
             <link>http://www.CircuitDB.com/circuits/id/263</link>
             <pubDate>Tue, 26 Feb 2008 09:05:50 +0100</pubDate>
             <guid><guid>http://www.CircuitDB.com/circuits/id/263</guid></guid>
             <description><![CDATA[This circuit will give you a feel for how the touch plate works in a circuit and you can expand on the circuit to suit your project needs. The touch plate can be a small piece of metal or aluminum foil. Start the circuit by moving S2 to the set position and then back to the previous position. Now press S1. One of the LED's will light. Now touch the touch plate and the LED's will flip on the opposite way. The sensitivity of the plate will vary depending on the humidity. Adjust the VR and capacitor that is connected to S2 to adjust the sensitivity.

Copyright 2001 [url=http://home.maine.rr.com/randylinscott/index.html]Randy Linscott[/url]]]></description>
          </item>
          <item>
             <title>Automotive Speed Indicator</title>
             <link>http://www.CircuitDB.com/circuits/id/262</link>
             <pubDate>Sun, 24 Feb 2008 18:02:35 +0100</pubDate>
             <guid><guid>http://www.CircuitDB.com/circuits/id/262</guid></guid>
             <description><![CDATA[The speed of an automobile can be indicated by detecting the pulses generated by the ignition system and causing an LED to light. The circuit utilizes a quad NOR gate IC chip. Two of the gates are configured as a one shot multivibrator which produces a fixed duration pulse each time the primary circuit of the automobile ignition system opens the circuit to the ignition coil. The other 2 gates are used as buffers which provide an accurate rectangle pulse. As the number of pulses per second increases, the voltage fed to the base of of the NPN transistor becomes high enough to cause it to conduct and turn on the LED. The speed at which the LED lights is set by R4. The input of the circuit is connected to the distributor side of the ignition coil or to the tachometer connection on those cars that are equipped with electronic ignition.

Copyright 2001 [url=http://home.maine.rr.com/randylinscott/index.html]Randy Linscott[/url]]]></description>
          </item>
          <item>
             <title>American police car siren</title>
             <link>http://www.CircuitDB.com/circuits/id/261</link>
             <pubDate>Fri, 22 Feb 2008 08:19:53 +0100</pubDate>
             <guid><guid>http://www.CircuitDB.com/circuits/id/261</guid></guid>
             <description><![CDATA[This circuit simulates the siren of an American police car. It uses two 555 timers in the circuit. The 555 on the right is wired as an alarm tone generator and the second 555 timer on the left is wired as a low frequency astable timer which generates a ramp waveform of about 6 seconds that is buffered by the transistor and again used to frequency modulate the tone generator. The transistor is used to help strengthen the signal to the speaker.

Copyright 2001 [url=http://home.maine.rr.com/randylinscott/index.html]Randy Linscott[/url]]]></description>
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          <item>
             <title>Star Trek "Red Alert" siren</title>
             <link>http://www.CircuitDB.com/circuits/id/260</link>
             <pubDate>Wed, 20 Feb 2008 06:55:45 +0100</pubDate>
             <guid><guid>http://www.CircuitDB.com/circuits/id/260</guid></guid>
             <description><![CDATA[This circuit simulates the &quot;Red Alert&quot; siren from the TV show Star Trek. It uses two 555 timers in the circuit. The 555 on the right is wired as an alarm tone generator and the second 555 timer on the left is wired as a 1.5 second non-symmetrical astable that generates a fast rising but slow falling saw tooth waveform. This waveform is buffered by the transistor and used to frequency modulate the tone generator and making its frequency rise slowly during the falling parts of the saw tooth but collapse rapidly during the rising part of the saw tooth. The output starts as a low frequency, rises for 1.15 seconds to a high tone, ceases for .35 seconds and then repeats the cycle.

Copyright 2001 [url=http://home.maine.rr.com/randylinscott/index.html]Randy Linscott[/url]]]></description>
          </item>
          <item>
             <title>British police car siren</title>
             <link>http://www.CircuitDB.com/circuits/id/259</link>
             <pubDate>Tue, 19 Feb 2008 21:32:14 +0100</pubDate>
             <guid><guid>http://www.CircuitDB.com/circuits/id/259</guid></guid>
             <description><![CDATA[This circuit simulates the siren of a British police car. It uses two 555 timers in the circuit. The 555 on the right is wired as an alarm tone generator and the second 555 timer on the left is a 1 Hz astable multivibrater. The output of the left timer is to frequency modulate the right timer. This causes the right timers frequency to alternate between 440Hz and 550Hz at a 1 Hz cyclic rate. The transistor is used to help strengthen the signal to the speaker.

Copyright 2001 [url=http://home.maine.rr.com/randylinscott/index.html]Randy Linscott[/url]]]></description>
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          <item>
             <title>12 Volt to 120 Volt Inverter</title>
             <link>http://www.CircuitDB.com/circuits/id/258</link>
             <pubDate>Sat, 09 Feb 2008 07:53:03 +0100</pubDate>
             <guid><guid>http://www.CircuitDB.com/circuits/id/258</guid></guid>
             <description><![CDATA[Ever needed a low power 120volt AC  power source for your car, van or truck? Well this circuit should do the trick for you. It will supply 15 watts of AC power to a device. It should power lamps, shavers, small stereos and small appliances. If you draw to much power the circuit will shut down all by itself. The output of this circuit is a square wave so there may be some noticeable hum on audio units plugged into it. To reduce some of the hum increase the value of the output capacitor which is at .47uf now. That transistor in the circuit are high power PNP transistors. Radio Shack part number 276-2025 are good ones to use or TIP32. The transformer is a 24 volt 2 amp center tapped secondary Radio Shack part number 273-1512 or equivalent.

Copyright 2001 [url=http://home.maine.rr.com/randylinscott/index.html]Randy Linscott[/url]]]></description>
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