{"id":699,"date":"2011-11-02T17:04:29","date_gmt":"2011-11-02T17:04:29","guid":{"rendered":""},"modified":"2017-12-10T17:07:56","modified_gmt":"2017-12-10T17:07:56","slug":"annunciator-control-circuit-ve","status":"publish","type":"post","link":"http:\/\/jasonbeaver.com\/rv7\/2011\/11\/02\/annunciator-control-circuit-ve\/","title":{"rendered":"Annunciator Control Circuit (Version 2)"},"content":{"rendered":"

I mentioned a few weeks ago that there was a flaw in my annunciator control circuit. \u00a0I redesigned it to provide a pull down resistor for the transistor base and a pull up resistor for the transistor collector. \u00a0I received the circuits yesterday and quickly assembled one, but it was not working as expected. \u00a0It was late, so I put it off until tonight.<\/p>\n

I got started tonight trying to diagnose the misbehaving circuit. \u00a0The first three annunciator lights were working as expected, but all of the others (both some high and some low triggers) were misbehaving. \u00a0I measured the voltages at various points in the circuit, but they really didn’t make sense. \u00a0It was almost as if I had installed PNP transistors instead of NPN transistors. \u00a0I checked the bag from Radio Shack and they were indeed NPN. \u00a0I breadboarded a single light control circuit and still<\/b>\u00a0couldn’t get it to work properly. \u00a0At this point, I was beginning to wonder if I had completely forgotten my circuit design skills from university. \u00a0I was disassembling the breadboard circuit and noticed that the transistor was smoking hot. \u00a0This shouldn’t have happened because the transistor should either be fully off or fully saturated. \u00a0In either case, the power dissipated in the transistor should have been essentially zero.<\/p>\n

It was really starting to seem like the only explanation was that it was a PNP transistor. \u00a0I looked up the part number on the transistor, and sure enough it was a PNP. \u00a0I went through the whole bag from Radio Shack and sure enough, every transistor was a PNP despite the bag indicating they were NPN. \u00a0I started desoldering the transistors off of the board and noticed the first three (the circuits that worked) were NPNs that I had left over from the first circuit I built. \u00a0This really pissed me off. \u00a0I wasted hours trying to diagnose a problem caused by Radio Shack’s mislabeled transistors.<\/p>\n

Anyway, I replaced all of the incorrect transistors and unsurprisingly, the circuit worked flawlessly. \u00a0All of the annunciator lights have nice sharp on\/off transitions and work exactly as expected.<\/p>\n

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

I mentioned a few weeks ago that there was a flaw in my annunciator control circuit. \u00a0I redesigned it to provide a pull down resistor for the transistor base and a pull up resistor for the transistor collector. \u00a0I received the circuits yesterday and quickly assembled one, but it was not working as expected. \u00a0It … Read More<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8],"tags":[],"class_list":["post-699","post","type-post","status-publish","format-standard","hentry","category-avionics"],"_links":{"self":[{"href":"http:\/\/jasonbeaver.com\/rv7\/wp-json\/wp\/v2\/posts\/699","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/jasonbeaver.com\/rv7\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/jasonbeaver.com\/rv7\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/jasonbeaver.com\/rv7\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/jasonbeaver.com\/rv7\/wp-json\/wp\/v2\/comments?post=699"}],"version-history":[{"count":4,"href":"http:\/\/jasonbeaver.com\/rv7\/wp-json\/wp\/v2\/posts\/699\/revisions"}],"predecessor-version":[{"id":3273,"href":"http:\/\/jasonbeaver.com\/rv7\/wp-json\/wp\/v2\/posts\/699\/revisions\/3273"}],"wp:attachment":[{"href":"http:\/\/jasonbeaver.com\/rv7\/wp-json\/wp\/v2\/media?parent=699"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/jasonbeaver.com\/rv7\/wp-json\/wp\/v2\/categories?post=699"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/jasonbeaver.com\/rv7\/wp-json\/wp\/v2\/tags?post=699"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}