{"id":159,"date":"2015-05-01T19:28:41","date_gmt":"2015-05-01T17:28:41","guid":{"rendered":"http:\/\/tronche.com\/blog\/?p=159"},"modified":"2019-01-20T13:39:26","modified_gmt":"2019-01-20T12:39:26","slug":"satellite-modem-mcu-communication-problem-solved","status":"publish","type":"post","link":"https:\/\/tronche.com\/blog\/2015\/05\/satellite-modem-mcu-communication-problem-solved\/","title":{"rendered":"satellite modem &#8211; MCU communication problem solved"},"content":{"rendered":"\n<p>I started by replacing the modem with a trusty GPS, so\n<\/p>\n\n\n\n<ol class=\"wp-block-list\"><li>I have a continuous flow of data<\/li><li>with a checksum (GPS lines are checksumed)<\/li><li>from a device that I know is working.<\/li><\/ol>\n\n\n\n<p>By counting the checksum errors, I have a huge number of them \n=&gt; this is not the modem, at least not alone, nor a problem with \nfloating input.\n<\/p>\n\n\n\n<p>By reading the TX line with a small oscilloscope, I can see the signal is very noisy.\n<\/p>\n\n\n\n<p>I now power both the GPS and the Teensy from the same source: the\n Teensy as a 3.3v output line which I&#8217;m using to power the GPS =&gt; \neverything is ok.\n<\/p>\n\n\n\n<p>So the problem was that, by powering the two devices from two \ndifferent sources, they got different 0 volt levels, making the signal \nvalue unpredictable. \n<\/p>\n\n\n\n<p>I tried again with different power sources, but by linking the \ntwo 0 volt lines together. I can now see on the oscilloscope that I got I\n nice square signal, but the serial data are corrupted from the uC point\n of view, so I&#8217;ll need to investigate this part further.\n<\/p>\n\n\n\n<p>For the balloon, this is not a problem, since everything will be \npowered from the same source. This isn&#8217;t done for the Teensy yet, \nbecause I need a USB cable that I can salvage and that I haven&#8217;t yet.<\/p>\n","protected":false},"excerpt":{"rendered":"<div class=\"mh-excerpt\"><p>I started by replacing the modem with a trusty GPS, so I have a continuous flow of data with a checksum (GPS lines are checksumed) <a class=\"mh-excerpt-more\" href=\"https:\/\/tronche.com\/blog\/2015\/05\/satellite-modem-mcu-communication-problem-solved\/\" title=\"satellite modem &#8211; MCU communication problem solved\">[&#8230;]<\/a><\/p>\n<\/div>","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[20],"tags":[60,51,61,56,52],"class_list":["post-159","post","type-post","status-publish","format-standard","hentry","category-almabraxas","tag-electronic-noise","tag-gps","tag-power-source","tag-satellite-modem","tag-teensy"],"_links":{"self":[{"href":"https:\/\/tronche.com\/blog\/wp-json\/wp\/v2\/posts\/159","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/tronche.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/tronche.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/tronche.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/tronche.com\/blog\/wp-json\/wp\/v2\/comments?post=159"}],"version-history":[{"count":1,"href":"https:\/\/tronche.com\/blog\/wp-json\/wp\/v2\/posts\/159\/revisions"}],"predecessor-version":[{"id":160,"href":"https:\/\/tronche.com\/blog\/wp-json\/wp\/v2\/posts\/159\/revisions\/160"}],"wp:attachment":[{"href":"https:\/\/tronche.com\/blog\/wp-json\/wp\/v2\/media?parent=159"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/tronche.com\/blog\/wp-json\/wp\/v2\/categories?post=159"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/tronche.com\/blog\/wp-json\/wp\/v2\/tags?post=159"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}