{"id":7667,"date":"2013-06-19T07:53:25","date_gmt":"2013-06-19T14:53:25","guid":{"rendered":"http:\/\/rustybolt.info\/wordpress\/?p=7667"},"modified":"2013-06-22T08:41:59","modified_gmt":"2013-06-22T15:41:59","slug":"2013-06-19-simple-inductance-meter-uses-dmm-for-readout","status":"publish","type":"post","link":"https:\/\/rustybolt.info\/wordpress\/?p=7667","title":{"rendered":"2013-06-19 Simple Inductance Meter Uses DMM for Readout"},"content":{"rendered":"

Kirk sent me a link to a simple, inexpensive L meter that uses your DMM as the readout<\/a> (see side note below).\u00a0 I should say that eBay has more than one seller that sells the LC meter that’s on a small PC board with its own display, and runs off of the USB port.\u00a0 The cost is about $30 U.S., so it may be easier to just buy one of these already assembled.<\/p>\n

That said, here’s my two cents’ worth of what I found by looking at the schematic.\u00a0 First off, the schematic shows the regulator chip s LM7805, which is the full size version which is wasteful of battery power.\u00a0 It should be the LM78L05, which is the small, low power version which will save a lot of battery current.\u00a0 And it’s shameful that the author did not include a 0.1 uF bypass capacitor at both the input and output of the 78L05, as is required<\/span> in the data sheet.\u00a0 As a result, the circuit could become unstable – timing is critical for an accurate reading.\u00a0 So add a ceramic bypass cap to both.<\/p>\n

There are four gates on the ‘LS132, and all four have one of the gates tied to +5V, which means that all four are being used as simple Schmitt inverters.\u00a0 So a Hex Schmitt Inverter would work just as well, with two gates left over.<\/p>\n

The two timing capacitors C1 and C3 should be 102J and 103J, the J meaning that the tolerance is 5%.\u00a0 Or even better, use 1% capacitors if you can find them.\u00a0 The capacitors should be stable when the temperature changes, so the readings will stay accurate.<\/p>\n

Another thing<\/strong> I don’t think is necessary.\u00a0 The regulated 5V goes through R5, a 100k resistor to D1, a 1N4148 diode.\u00a0 This acts as a second regulator, with a voltage drop of about a half volt.\u00a0 Then it goes through another resistor, the 33k R2.\u00a0 By the time it gets to R1, the zero adjust pot, it is only a few millivolts.\u00a0 Why should there be a need for the D1?\u00a0 The 5V is already regulated and stable, so why not just put one larger resistor in place of R5, D1 and R2?\u00a0 The voltage at the R1 pot would be just as stable.\u00a0 The only thing I can think of is that the D1 diode forward voltage varies with the temperature, so it gives some temperature compensation.\u00a0 But the amount of voltage change at the wiper of R1 must be very small, only microvolts.\u00a0 I would try it without the D1 and with just a single resistor.\u00a0 And I would also put a 0.1 uF bypass capacitor from the wiper of R1 to negative.<\/p>\n

A side note: the link above is to a website of “rstevew”, AKA R. Steven Walz.\u00a0 In the 1990s, I used to hang out on the Usenet newsgroups sci.electronics.* and alt.binaries.schematics.electronics.\u00a0 The newsgroups were unmoderated, and no one could keep the bad people out of them.\u00a0 There were a few very knowledgeable and helpful people, such as Winfield Hill and Jim Thompson, and I forget his name, from Austin Instruments. \u00a0 But there were a few irascible trolls, one of them being Walz, who took no prisoners when it came to giving people a hard time.\u00a0 I think the others tolerated Walz because he kept a lot of good stuff on his website.\u00a0 But other than that, I refused to return the bad words he threw out at people, because if you respond to the trolls, they want attention and only respond with more of the same.\u00a0 After a few years, I quit visiting those newsgroups because of the trolls, and stayed away for more than five years.\u00a0 Then I happened to have a PC that could access the newsgroups, and I revisited them again.\u00a0 What did I find?\u00a0 The same rubbish, from the same trolls.\u00a0 So I promptly left, and I haven’t been back since.\u00a0 That was more than ten years ago, and I have since saved a huge amount of time by quitting.\u00a0 Now there are thousands of forums out there that are moderated, and other blogs like mine that are administered by someone who filters out all of the trash.\u00a0 The Usenet newsgroups were a treasure trove of information in their time, but the spammers and trolls made them intolerable and one never hears about them nowadays, most likely for those reasons.\u00a0 Good riddance, I say.<\/p>\n

As another side note, I joined a Yahoo group, and they have banned any Grouply members.\u00a0 Apparently the Grouply member has to give his Yahoo user name and password to Grouply.\u00a0 Then Grouply uses it to do its thing, which apparently isn’t to the liking of some, and most probably violates the Yahoo Terms of Service.\u00a0 I’m not a Grouply member so I don’t all the details, but check this out before you decide to join.<\/p>\n","protected":false},"excerpt":{"rendered":"

Kirk sent me a link to a simple, inexpensive L meter that uses your DMM as the readout (see side note below).\u00a0 I should say that eBay has more than one seller that sells the LC meter that’s on a small PC board with its own display, and runs off of the USB port.\u00a0 The <\/p>\n

(Read More…)<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17],"tags":[],"class_list":["post-7667","post","type-post","status-publish","format-standard","hentry","category-meters-and-test-equipment"],"_links":{"self":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/7667","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=7667"}],"version-history":[{"count":11,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/7667\/revisions"}],"predecessor-version":[{"id":7669,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/7667\/revisions\/7669"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=7667"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=7667"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=7667"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}