{"id":5559,"date":"2012-12-30T20:58:26","date_gmt":"2012-12-31T04:58:26","guid":{"rendered":"http:\/\/rustybolt.info\/wordpress\/?p=5559"},"modified":"2013-01-02T05:49:43","modified_gmt":"2013-01-02T13:49:43","slug":"2012-12-30-light-deactivated-alarm","status":"publish","type":"post","link":"https:\/\/rustybolt.info\/wordpress\/?p=5559","title":{"rendered":"2012-12-30 Light Deactivated Alarm"},"content":{"rendered":"<p><a href=\"http:\/\/rustybolt.info\/wordpress\/?attachment_id=5594\" rel=\"attachment wp-att-5594\"><img loading=\"lazy\" decoding=\"async\" class=\"alignright size-medium wp-image-5594\" title=\"DSC_0009S\" src=\"http:\/\/rustybolt.info\/wordpress\/wp-content\/uploads\/2012\/12\/DSC_0009S-300x220.jpg\" alt=\"\" width=\"300\" height=\"220\" srcset=\"https:\/\/rustybolt.info\/wordpress\/wp-content\/uploads\/2012\/12\/DSC_0009S-300x220.jpg 300w, https:\/\/rustybolt.info\/wordpress\/wp-content\/uploads\/2012\/12\/DSC_0009S.jpg 800w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a>This light deactivated alarm (or should it be called a dark activated alarm?) might be used as a detector when a light beam is broken.\u00a0 I would use a red LED and restrict the light to a narrow beam so that it would be hard to see.\u00a0 When the CdS cell is illuminated and the circuit is deactivated the current drawn is only a few tens of microamps depending on where the 1 meg pot is set.<\/p>\n<p>The two middle transistors are basically an astable multivibrator, with the 100k base bias resistor of the left transistor going to the collector of the PNP transistor, which acts as a switch to turn\u00a0 it on when the photocell is unlit.\u00a0 The right transistor is driven through the 100nF and directly drives the 9 ohm speaker.\u00a0 This transistor has no base bisa; it is running as a switch so it should not get hot.\u00a0 The 33 ohm resistor in series with the speaker limits the current through the speaker so that it doesn&#8217;t sound too loud and so it doesn&#8217;t overheat.<\/p>\n<p>I once built a similar circuit using a small 1.5 inch speaker rated at about 0.2 watts.\u00a0 After a short time, the speaker voice coil went open, probably from excessive current and temperature.\u00a0 So if you decide to leave out the 33 ohm resistor, you should consider using a speaker capable of handling much more than 0.2 watts.\u00a0 Also, the 2N3053 is expensive and not easily obtained.\u00a0 I would suggest using a BD135 and small heatsink if it gets hot.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>This light deactivated alarm (or should it be called a dark activated alarm?) might be used as a detector when a light beam is broken.\u00a0 I would use a red LED and restrict the light to a narrow beam so that it would be hard to see.\u00a0 When the CdS cell is illuminated and the<a href=\"https:\/\/rustybolt.info\/wordpress\/?p=5559\"> <\/p>\n<p> (Read More&#8230;)<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[13,129],"tags":[],"class_list":["post-5559","post","type-post","status-publish","format-standard","hentry","category-lighting","category-security-and-safety"],"_links":{"self":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/5559","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5559"}],"version-history":[{"count":14,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/5559\/revisions"}],"predecessor-version":[{"id":5592,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/5559\/revisions\/5592"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5559"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5559"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5559"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}