(More about analogReference<\/span> can be read at https:\/\/www.arduino.cc\/en\/Reference\/AnalogReference)<\/p>\n The simple voltmeter described in a previous article<\/a> has been modified here. It is now supplied with a precise reference voltage at the AREF pin.<\/p>\n The 5K resistance is not a necessity, it has been added for safety (switching to the INTERNAL while external power is given to AREF can damage the board with that resistance<\/em>). If the resistance is used then the voltage at AREF will not be exact as supplied. That is because internally there is a 32k resistor connected to the AREF pin.<\/p>\n So in above case the voltage that the AREF actually getting is 3.3*32\/(32+5) = 2.8540 (the actual will vary due to tolerance of components, so for cases where high precision is needed, the values of the resistors will have to be measured and also the voltage of the zener, and the voltage in the code nees to be changed accordingly).<\/p>\n On some Arduino boards there is a Pin labelled as AREF or Analog Reference. This pin is very useful in cases where a stable and precise voltage reference is needed for the ADC. Practically the supplied voltage to the board can vary a bit, specially it can fall below the rated voltage depending on the… Continue reading Arduino Voltmeter – 2 (more precise)<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[10],"tags":[74],"class_list":["post-470","post","type-post","status-publish","format-standard","hentry","category-arduino","tag-arduino-voltmeter","entry"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.kolkataonweb.com\/code-bank\/wp-json\/wp\/v2\/posts\/470","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.kolkataonweb.com\/code-bank\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.kolkataonweb.com\/code-bank\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.kolkataonweb.com\/code-bank\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.kolkataonweb.com\/code-bank\/wp-json\/wp\/v2\/comments?post=470"}],"version-history":[{"count":5,"href":"https:\/\/www.kolkataonweb.com\/code-bank\/wp-json\/wp\/v2\/posts\/470\/revisions"}],"predecessor-version":[{"id":497,"href":"https:\/\/www.kolkataonweb.com\/code-bank\/wp-json\/wp\/v2\/posts\/470\/revisions\/497"}],"wp:attachment":[{"href":"https:\/\/www.kolkataonweb.com\/code-bank\/wp-json\/wp\/v2\/media?parent=470"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.kolkataonweb.com\/code-bank\/wp-json\/wp\/v2\/categories?post=470"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.kolkataonweb.com\/code-bank\/wp-json\/wp\/v2\/tags?post=470"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}Please note the voltage at AREF can 0-5 volts only and the input voltage at the I\/O pin (here A0) cannot exceed that of the AREF pin.<\/pre>\n
![\"Volt](\"https:\/\/www.kolkataonweb.com\/code-bank\/wp-content\/uploads\/2016\/08\/Volt-Meter-Precise-1024x633.png\")
<\/a><\/p>\n#define<\/span> READINGS <\/span>5<\/span>\r\n\r\nint<\/span> sensorPin <\/span>=<\/span> A0<\/span>;<\/span>\r\nshort<\/span> int<\/span> readingsTaken <\/span>=<\/span> 0<\/span>;<\/span>\r\nfloat<\/span> voltage <\/span>=<\/span> 0.0<\/span>,<\/span> readingTotal <\/span>=<\/span> 0.0<\/span>;<\/span>\r\n\r\nvoid<\/span> setup<\/span>()<\/span> {<\/span>\r\n\u00a0 <\/span>\/\/ put your setup code here, to run once:<\/span>\r\n\u00a0 pinMode<\/span>(<\/span>sensorPin<\/span>,<\/span> INPUT<\/span>);\r\n analogReference(EXTERNAL);<\/span>\r\n\u00a0 <\/span>Serial<\/span>.<\/span>begin<\/span>(<\/span>9600<\/span>);<\/span>\r\n}<\/span>\r\n\r\nvoid<\/span> loop<\/span>()<\/span> {<\/span>\r\n\u00a0 <\/span>\/\/ put your main code here, to run repeatedly:<\/span>\r\n\u00a0 readingTotal <\/span>=<\/span> 0.0<\/span>;<\/span>\r\n\u00a0 readingsTaken <\/span>=<\/span> 0<\/span>;<\/span>\r\n\u00a0 \r\n\u00a0 <\/span>\/\/ we will take 5 readings at 1 sec interval and then do an average of that<\/span>\r\n while<\/span>(<\/span>readingsTaken <\/span><<\/span> READINGS<\/span>)<\/span> \r\n\u00a0 <\/span>{<\/span>\r\n\u00a0\u00a0\u00a0 readingTotal <\/span>+=<\/span> analogRead<\/span>(<\/span>sensorPin<\/span>);<\/span>\r\n\u00a0\u00a0\u00a0 readingsTaken<\/span>++;<\/span>\r\n\u00a0\u00a0\u00a0 delay<\/span>(<\/span>1000<\/span>);<\/span> \/\/at every 1 second interval<\/span>\r\n\u00a0 <\/span>}<\/span>\r\n\r\n\u00a0 voltage <\/span>=<\/span> (<\/span>readingTotal<\/span>\/<\/span>READINGS<\/span>)<\/span> *<\/span> (<\/span>2.8540<\/span>\/<\/span>1024<\/span>);<\/span> \/\/ 2.8540 is the ref voltage being used. \/\/the value in voltage at this point is what Arduino read based on input from voltage divider network. Need to calculate the original<\/span> -- see below\r\n\r\n<\/span> voltage <\/span>=<\/span> (<\/span>20<\/span>\/<\/span>2.609)<\/span> *<\/span> voltage<\/span>;<\/span> \/\/unitary method to calculate the actual voltage that is read. When voltage read is 2.609, the input is 20v. With the above voltage divider used at input (100K ohm and 15k ohm) the input voltage at the I\/O (pin A0) will be 2.609 when 20v is applied. \r\n<\/span> \u00a0 \r\n<\/span> Serial<\/span>.<\/span>println<\/span>(<\/span>voltage<\/span>);<\/span> \r\n}<\/span><\/pre>\n","protected":false},"excerpt":{"rendered":"