{"id":8780,"date":"2007-05-14T18:12:00","date_gmt":"2007-05-14T22:12:00","guid":{"rendered":"https:\/\/nuxx.net\/blog\/2007\/05\/14\/electronics-help-current-loop\/"},"modified":"2026-07-01T11:35:28","modified_gmt":"2026-07-01T15:35:28","slug":"electronics-help-current-loop","status":"publish","type":"post","link":"https:\/\/nuxx.net\/blog\/2007\/05\/14\/electronics-help-current-loop\/","title":{"rendered":"Electronics Help: Current Loop"},"content":{"rendered":"<p>Staying late at work today I set about turning <a href=\"https:\/\/nuxx.net\/blog\/wp-content\/uploads\/2026\/06\/IMG_7204-scaled.jpg\">this PCB<\/a> into <a href=\"http:\/\/nuxx.net\/images\/cl_schem_firstdraft.png\">this schematic<\/a>. (I also replaced the MC1488 \/ MC1489 combo with a MAX232, eliminating the need for a bunch of diodes and feeding the board +\/-15VDC.)<\/p>\n<p>It supposedly turns RS232 into current loop, where amperage is used to signal 0 or 1 instead of voltage. This makes the signal more robust in noisy environments or with long wire runs.<\/p>\n<p>The thing is, when I look at this, I can&#8217;t quite see it as being anything more than a device which takes RS232 serial and converts it to be 0V or 30V (for low or high), and optically isolates data going back to the PC. I don&#8217;t see any way it actually varies the amperage while keeping the voltage steady.<\/p>\n<p>Can someone correct me, or confirm what I&#8217;m seeing? The schematic, as made from the board, is <a href=\"http:\/\/nuxx.net\/images\/cl_schem_firstdraft.png\">here<\/a>.<\/p>\n<p>(Also, I need to remove the 7486 part. Each currently grounded leg of the gate was originally set to a jumper to select if it should be high or low, but the needs of this board are fine having them all grounded. As it&#8217;s XOR on all of them, and one leg is always pulled low, the output will always be whatever the input is. So, I think I can eliminate the 7486. I believe the jumpers serve to invert the signal, should it be needed. But it&#8217;s not. And I didn&#8217;t remove the 7486 while removing the jumpers because I wasn&#8217;t certain of it was used for anothing else. But now I know. And knowing is half the battle.)<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Staying late at work today I set about turning this PCB into this schematic. (I also replaced the MC1488 \/ MC1489 combo with a MAX232, eliminating the need for a bunch of diodes and feeding the board +\/-15VDC.) It supposedly turns RS232 into current loop, where amperage is used to signal 0 or 1 instead\u2026<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6,34],"tags":[],"class_list":["post-8780","post","type-post","status-publish","format-standard","hentry","category-electronics","category-moved-from-livejournal"],"_links":{"self":[{"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/posts\/8780","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/comments?post=8780"}],"version-history":[{"count":1,"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/posts\/8780\/revisions"}],"predecessor-version":[{"id":12850,"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/posts\/8780\/revisions\/12850"}],"wp:attachment":[{"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/media?parent=8780"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/categories?post=8780"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/nuxx.net\/blog\/wp-json\/wp\/v2\/tags?post=8780"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}