{"id":123,"date":"2014-01-13T16:45:07","date_gmt":"2014-01-13T16:45:07","guid":{"rendered":"http:\/\/192.168.3.4\/?p=123"},"modified":"2018-01-09T06:48:22","modified_gmt":"2018-01-09T14:48:22","slug":"sniffing-the-planet-bike-blaze-1w-headlight","status":"publish","type":"post","link":"https:\/\/www.cloudacm.com\/?p=123","title":{"rendered":"Sniffing the Planet Bike Blaze 1W Headlight"},"content":{"rendered":"

I decided to see if the Planet Bike Blaze 1W Headlight<\/a> had some PWM going on behind the scenes. It seemed to me that the logic analyzer would be perfect for this task.\u00a0 I was actually surprised by the results.\u00a0 One thing that I did decide on was using different test equipment in succession so nothing got smoked.<\/p>\n

First test was using the voltmeter.\u00a0 It could handle it, since the headlight was powered by 2 AA batteries in series, aka 3vdc.\u00a0 The voltmeter read 2.78vdc at the battery terminals of the source pack.\u00a0 Next I tested the low beam voltage, it read 2.65vdc.\u00a0 The high beam was 2.98vdc, interesting since the source pack was lower.\u00a0 Finally, the strobe beam measured in at 2.3vdc.\u00a0 Nothing fantastic here.<\/p>\n

\"VoltMeter\"<\/a><\/p>\n

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Next up was my Propscope (USB Oscilloscope made by Parallax)<\/a>.\u00a0 It confirmed that the off voltage was 0vdc and the high beam was 2.98vdc.\u00a0 However, the Low and Strobe beams had more interesting wave forms.<\/p>\n

\"LowOnDutyCycle\"<\/a><\/p>\n

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The low beam was a 164hz square wave 50% duty cycle.\u00a0 The artifacts in the square wave show some RC circuit in the mix.\u00a0 One other thing to note is the off portion of the duty isn’t really off, it hovers just above 2vdc.<\/p>\n

\"Strobe_FullDutyCycle\"<\/a><\/p>\n

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The strobe beam revealed some interesting on off blocks.\u00a0 There are 2 long strobes followed by 4 short strobes.\u00a0 The pulse width following each short strobe was 100ms.\u00a0 The pulse width between the rising edge of the first long strobe and the falling edge of the second long strobe was 200ms.\u00a0 It total time for each strobe loop measured 715ms.\u00a0 There is considerable amounts of noise that appears in the off state.\u00a0 Also, the short strobes are not even.<\/p>\n

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\"Strobe_ShortOffCycle\"<\/a><\/p>\n

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Zooming in to the short strobe showed that they are actually comprised of 3 pulses measuring 1.93ms each that are gaped with two 787us of off cycle.\u00a0 The total on time of the short strobe is 7.36ms.\u00a0 The low levels show a sawtooth pattern typical of a RC circuit.\u00a0 I’m assuming that this is some kind of charge pump<\/a> to maintain the voltage level on the LED.<\/p>\n

\"screenshot\"<\/a><\/p>\n

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It was a let down to find nothing detected on the logic probe.\u00a0 I had to cycle the headlight on and off just to get this measurement.\u00a0 I assumed that it would at least get the pulses from the strobe.\u00a0 The only thing I can conclude is that the logic probe needed a true low, not something hovering around 2vdc.\u00a0 It didn’t seem practical to add a bias just to get the logic probe to show the same thing the oscilloscope already had.<\/p>\n","protected":false},"excerpt":{"rendered":"

I decided to see if the Planet Bike Blaze 1W Headlight had some PWM going on behind the scenes. It seemed to me that the logic analyzer would be perfect for this task.\u00a0 I was actually surprised by the results.\u00a0 One thing that I did decide on was using different test equipment in succession so nothing got smoked. First test was using the voltmeter.\u00a0 It could handle it, since the headlight was powered by 2 AA batteries in series, aka…<\/p>\n

Read More Read More<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3],"tags":[],"class_list":["post-123","post","type-post","status-publish","format-standard","hentry","category-rd"],"_links":{"self":[{"href":"https:\/\/www.cloudacm.com\/index.php?rest_route=\/wp\/v2\/posts\/123","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.cloudacm.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.cloudacm.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.cloudacm.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.cloudacm.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=123"}],"version-history":[{"count":11,"href":"https:\/\/www.cloudacm.com\/index.php?rest_route=\/wp\/v2\/posts\/123\/revisions"}],"predecessor-version":[{"id":141,"href":"https:\/\/www.cloudacm.com\/index.php?rest_route=\/wp\/v2\/posts\/123\/revisions\/141"}],"wp:attachment":[{"href":"https:\/\/www.cloudacm.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=123"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.cloudacm.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=123"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.cloudacm.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=123"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}