Often an experimenter needs a variable resistance and adds a trimpot to the circuit.\u00a0 For instance I want a resistor that can be varied between 220 and 330 ohms.\u00a0 The easiest solution would be a 220 ohm resistor and a 100 ohm trimpot in series.\u00a0 But I don’t have a 100 ohm trimpot, which is a very uncommon value.\u00a0 I have a 1000 ohm trimpot, so can I use that instead?<\/p>\n
Let’s see how we can do that.\u00a0 The circuit doesn’t say that the resistor or trimpot has to be a single part.\u00a0 You can put two resistors in parallel and get 220 or 330 ohms.\u00a0 Let’s try this: leave the 220 ohm resistor to be the minimum, and replace the 100 ohm trimpot (that would have been in series) with two resistors that can be varied between 0 and 100 ohms.<\/p>\n
I take a guess at the resistor that I want to go in parallel with the 1000 ohm pot.\u00a0 I guess 150 ohms.\u00a0 So I take my calculator and enter 150 and press the 1\/X key.\u00a0 Then I press + and enter 1000 and pres the 1\/X key.\u00a0 Then I press the = key and 1\/X key and I get 130.43 ohms.<\/p>\n
That’s a bit too high, so I take another guess, and enter 120 into the calculator and press the 1\/X key and + key.\u00a0 Then I enter 1000 and press 1\/X key, press the = key and then 1\/X key.\u00a0 I get 107.14 ohms.\u00a0 That’s just about right for the maximum.<\/p>\n
As I vary the 1000 ohm trimpot, which is in parallel with the 120 ohm resistor, it is going to give a resistance that is between 0 and 107 ohms.\u00a0 The linearity of the pot will be affected.\u00a0 The resistance will change less at the high resistance end of the trimpot, and change more at the low end of the trimpot.\u00a0 But we can now use a 1000 ohm trimpot to do the job of a 100 ohm trimpot.<\/p>\n
Any two resistors in parallel can be found by adding their conductances.\u00a0 The conductance is equal to 1 divided by the resistance.\u00a0 So before adding the resistance you entered, you press the 1\/X key to change it to conductance.\u00a0 The unit of conductance is the Siemens, which at one time was called the Mho.\u00a0 This procedure also works for capacitors in series.\u00a0 But if you have two resistors or capacitors of the same value, just divide that value by two.\u00a0 Two 1000 ohm resistors in parallel equal 500 ohms, etc.<\/p>\n
Back to experimenting…<\/p>\n","protected":false},"excerpt":{"rendered":"
Often an experimenter needs a variable resistance and adds a trimpot to the circuit.\u00a0 For instance I want a resistor that can be varied between 220 and 330 ohms.\u00a0 The easiest solution would be a 220 ohm resistor and a 100 ohm trimpot in series.\u00a0 But I don’t have a 100 ohm trimpot, which is <\/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":[1],"tags":[],"class_list":["post-7955","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/7955","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=7955"}],"version-history":[{"count":7,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/7955\/revisions"}],"predecessor-version":[{"id":8022,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/7955\/revisions\/8022"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=7955"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=7955"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=7955"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}