{"id":2521,"date":"2012-05-01T08:00:39","date_gmt":"2012-05-01T15:00:39","guid":{"rendered":"http:\/\/rustybolt.info\/wordpress\/?p=2521"},"modified":"2012-06-08T00:21:32","modified_gmt":"2012-06-08T07:21:32","slug":"2012-05-01","status":"publish","type":"post","link":"https:\/\/rustybolt.info\/wordpress\/?p=2521","title":{"rendered":"2012-05-01 Light Sensor Circuit"},"content":{"rendered":"

I watched this video on Youtube called Light Sensor Making Steps<\/strong><\/a>.\u00a0 He shows a schematic at the beginning.\u00a0 The problem is that when the light is bright, the CdS “LDR ” photocell’s resistance can go well below 1000 ohms, and then the photocell is passing as much or more current as the LED is using.\u00a0 The total current to the circuit is much more than the LED current, and it is very wasteful, especially if the circuit is being powered by a battery, which will be drained much faster.<\/p>\n

So I thought I should come up with a better circuit \"\"<\/a>.\u00a0 And it doesn’t have to use a CdS photocell.\u00a0 Instead, it will use a red LED as a light sensor (see the schematic).<\/p>\n

Another<\/strong> alternative solution is to put a resistor in series with the CdS photocell, to limit the amount of current it passes.\u00a0 The transistor needs only a fraction of a milliamp to turn on and light the red LED.\u00a0 I would say insert a 3.3k resistor in series with the photocell, and see how it works.<\/p>\n

Also,<\/strong> remember that you do not have to source current through R2, you can sink current.\u00a0 Swap the Q1 and Q2 transistors.\u00a0 Put the BC557 first, with the cathode or flat spot of red LED connected to the base and the anode connected to +6V along with the BC557’s emitter.\u00a0 The BC557’s collector then connects to the 47k, which then connects to the BC547’s base.<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

I watched this video on Youtube called Light Sensor Making Steps.\u00a0 He shows a schematic at the beginning.\u00a0 The problem is that when the light is bright, the CdS “LDR ” photocell’s resistance can go well below 1000 ohms, and then the photocell is passing as much or more current as the LED is using.\u00a0 <\/p>\n

(Read More…)<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6,12,13],"tags":[],"class_list":["post-2521","post","type-post","status-publish","format-standard","hentry","category-electronics","category-led","category-lighting"],"_links":{"self":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/2521","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=2521"}],"version-history":[{"count":17,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/2521\/revisions"}],"predecessor-version":[{"id":3042,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/2521\/revisions\/3042"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2521"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2521"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2521"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}