tag:blogger.com,1999:blog-7294135473370786875.post1067572808113811237..comments2014-07-17T18:57:29.528-04:00Comments on Project Potpourri: Temperature Logging Part IDUhttp://www.blogger.com/profile/15427884103652875815noreply@blogger.comBlogger3125tag:blogger.com,1999:blog-7294135473370786875.post-4664061459847958222009-08-04T20:17:51.346-04:002009-08-04T20:17:51.346-04:00Heh, checking in again, almost exactly a year late...Heh, checking in again, almost exactly a year later. This blogonet is turning out pretty useful...DUhttps://www.blogger.com/profile/15427884103652875815noreply@blogger.comtag:blogger.com,1999:blog-7294135473370786875.post-80329542807662443602008-08-07T21:51:00.000-04:002008-08-07T21:51:00.000-04:00Further note to self: Measure the voltage across t...Further note to self: Measure the <B>voltage</B> across the photoresistor, not the resistance.DUhttps://www.blogger.com/profile/15427884103652875815noreply@blogger.comtag:blogger.com,1999:blog-7294135473370786875.post-42997625728810857512008-08-07T20:00:00.000-04:002008-08-07T20:00:00.000-04:00Me, checking in again! I needed this and looked i...Me, checking in again! I needed this and looked it up on my own blog!<BR/><BR/>Va = V * (r2/(r1+r2))<BR/><BR/>Where Va is the voltage at A1, V is 5V, r1 is the top resistor and r2 is the resistor I'm trying to measure.<BR/><BR/>The Arduino is going to read the input port and tell me, in increments of 1024, how close it is to 5V. So ideally, I'd like the max value of r2 to render r2/(r1+r2) = 1, meaning r1 should be small. The min value of r2 should give a total of close to 0, meaning r1 should dominate for r2 on the small end.<BR/><BR/>For my current needs, the varying resistor (a photoresistor) registers around 25k in the dark and around 200 in the light. If I use a 1k resistor for r1, then Va should vary from...5 * 200/1200 = .8V to 5 * 25000/26000 = 4.8V. OK.DUhttps://www.blogger.com/profile/15427884103652875815noreply@blogger.com