{"id":38,"date":"2010-11-02T00:40:42","date_gmt":"2010-11-02T07:40:42","guid":{"rendered":"http:\/\/www.mjblythe.com\/hacks\/?p=38"},"modified":"2021-12-22T00:01:01","modified_gmt":"2021-12-22T07:01:01","slug":"modifying-a-camera-flash-part-1","status":"publish","type":"post","link":"http:\/\/www.mjblythe.com\/hacks\/2010\/11\/modifying-a-camera-flash-part-1\/","title":{"rendered":"Modifying a camera flash &#8211; part 1"},"content":{"rendered":"<h2 id=\"Content\">WARNING<\/h2>\n<p>A camera flash uses high voltage, and a large capacitor. Even if the camera has been sitting around for a &#8220;long time&#8221;, the capacitor can still hold enough juice to give a good shock. In order to avoid this, be sure to fully discharge the capacitor by shorting the 2 terminals with a screwdriver or something. (But not your nice screwdriver&#8230;the arc can actually pit the metal)<\/p>\n<h2>Procurement<\/h2>\n<p>I was about to buy a disposable camera just to dismantle it, but it seemed a waste of $10 (or whatever it cost). I remembered a couple people mentioning that sometimes you could get them for free from photo labs, so I figured I&#8217;d give that a shot first.<\/p>\n<p>So I went to my local grocery store&#8217;s photo department, and asking if they had any &#8220;spent&#8221; disposable cameras. I felt a little foolish asking for what was essentially trash, so I described how I wanted the circuitry from them. I don&#8217;t really think it mattered, though. The guy behind the counter just brought the bin out for me and told me to have at it. Awesome!<\/p>\n<p>I ended up with 2 Kodaks and 1 Fuji.<\/p>\n<p><!--more--><\/p>\n<h2>Reverse engineering<\/h2>\n<p>Since I had 2 of the Kodaks (i.e. one extra to screw up), I figured I&#8217;d start there.<\/p>\n<p>The case pried apart easily enough, and it was easy to identify the main components of the circuit&#8230;Xenon tube, storage capacitor, battery, switches, etc. Most importantly, I found the contact that was made to trigger the flash. It was actually quite clever&#8230;the leaf shutter itself was part of the circuit, and when it was fully open, it would touch the other contact, closing the circuit and triggering the flash. I measured the voltage across this contact, and quickly realized why others that I&#8217;d found had used <a href=\"http:\/\/en.wikipedia.org\/wiki\/Silicon-controlled_rectifier\">SCRs<\/a>&#8230;it was about 300 volts!<\/p>\n<h2>My design<\/h2>\n<p>I had a couple requirements that I had in mind while designing my circuit:<\/p>\n<ul>\n<li>be able to turn it on and off\n<ul>\n<li>The original circuit was mysterious&#8230;if you kept taking pictures, it would keep recharging the flash. However, if you let it sit for a while, it would stop charging the flash, and the capacitor would gradually discharge. I wanted to control specifically when it is and is not charging.<\/li>\n<\/ul>\n<\/li>\n<li>be able to run off batteries or an external power source\n<ul>\n<li>It seems wasteful to keep replacing batteries on the thing&#8230;<\/li>\n<\/ul>\n<\/li>\n<li>be able to trigger a flash from a microcontroller pin\n<ul>\n<li>this also implies that I&#8217;d connect the flash&#8217;s ground to the same ground as a microcontroller, and I&#8217;d expect the flash to trigger from a +5VDC pulse with respect to that ground.<\/li>\n<\/ul>\n<\/li>\n<li>be able to trigger a flash manually\n<ul>\n<li>for testing &amp; to discharge the storage capacitor most of the way after turning it off to put it away or hack on the circuit some more<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p>Here&#8217;s what I came up with:<\/p>\n<p>FIXME: insert schematic here<\/p>\n<p>As you can see, there are 4 wires that I patched into from the original flash cirtuit:<\/p>\n<ul>\n<li>battery +<\/li>\n<li>power input\n<ul>\n<li>these two were formerly connected, but I removed the jumper wire so I could switch the power on &amp; off<\/li>\n<\/ul>\n<\/li>\n<li>ground (i.e. battery &#8211; )<\/li>\n<li>flash trigger\n<ul>\n<li>will activate when connected to ground<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p>Aside from removing the jumper between &#8220;battery +&#8221; and &#8220;power in&#8221;, I made one other change to the camera&#8217;s curcuit board: to make sure that the flash is always charging, I soldiered a jumper across the &#8220;flash charge&#8221; button contacts.<\/p>\n<p>Next, I wired it up, I put in a battery, and turned it on&#8230;<\/p>\n<h2>Results<\/h2>\n<p>After switching it on, I could hear the flash charge (the boost converter to charge the storage capacitor creates a lot of audible noise), so I knew I hadn&#8217;t screwed up too badly. However, when I pushed the button, nothing happened. After some frustrating debugging, I found the problem: I had the polarity wrong on the &#8220;trigger&#8221; wire. I had thought that it was +300VDC with respect to the &#8220;battery -&#8221; wire, but it was in fact at -300VDC. My SCR needed to go the other way around.<\/p>\n<p>Additionally, I found that when I hooked up an external power supply, the flash wouldn&#8217;t charge completely. I did some more measurements with a battery, and found that the flash drew about 2 Amps from the battery! My Linear regulator was only rated for 1A.<\/p>\n<p>Unfortunately, at this point, I gave up for a while. Switching the SCR around was non-trivial, and Halloween was arriving soon&#8230;too soon. I did manage to get it working when I tried again the next year.<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>WARNING A camera flash uses high voltage, and a large capacitor. Even if the camera has been sitting around for a &#8220;long time&#8221;, the capacitor can still hold enough juice to give a good shock. In order to avoid this, be sure to fully discharge the capacitor by shorting the 2 terminals with a screwdriver [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[7],"tags":[],"class_list":["post-38","post","type-post","status-publish","format-standard","hentry","category-howto"],"_links":{"self":[{"href":"http:\/\/www.mjblythe.com\/hacks\/wp-json\/wp\/v2\/posts\/38","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.mjblythe.com\/hacks\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.mjblythe.com\/hacks\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.mjblythe.com\/hacks\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.mjblythe.com\/hacks\/wp-json\/wp\/v2\/comments?post=38"}],"version-history":[{"count":6,"href":"http:\/\/www.mjblythe.com\/hacks\/wp-json\/wp\/v2\/posts\/38\/revisions"}],"predecessor-version":[{"id":190,"href":"http:\/\/www.mjblythe.com\/hacks\/wp-json\/wp\/v2\/posts\/38\/revisions\/190"}],"wp:attachment":[{"href":"http:\/\/www.mjblythe.com\/hacks\/wp-json\/wp\/v2\/media?parent=38"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.mjblythe.com\/hacks\/wp-json\/wp\/v2\/categories?post=38"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.mjblythe.com\/hacks\/wp-json\/wp\/v2\/tags?post=38"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}