{"id":58,"date":"2010-09-21T11:36:24","date_gmt":"2010-09-21T11:36:24","guid":{"rendered":"http:\/\/www.mariarabinovich.com\/physcomp\/?p=58"},"modified":"2011-02-05T17:54:07","modified_gmt":"2011-02-05T17:54:07","slug":"58","status":"publish","type":"post","link":"http:\/\/www.mariarabinovich.com\/blog\/archives\/58","title":{"rendered":"Analog Input Lab"},"content":{"rendered":"

[wpvideo TuIRJuC8]<\/p>\n

I was experimenting a little with putting several LEDs in series and parallel circuits controlled by the potentiometer, and I think this is true: with three LEDs wired serially, the same current is divided among them, so the more there are, the dimmer they get. The voltage is divided by all of the LEDs evenly because the current moves through each LED on its way to the next. This is the part that is less intuitive. I know that electricity flows in a path of least resistance, but why do the LEDs light up simultaneously at the same dimmer level instead of the first LED sucking up the maximum power and lighting up to its full potential, its like they know what is to come ahead for the entire length of the circuit. I guess maybe on an electron level its not simultaneous, and as the LED begins to light up it creates some kind of resistance, at which point the current wants to move on through the wire toward the next LED.<\/p>\n

When they are wired in parallel, this doesn’t happen because each LED gets the max amount of voltage, since it has a direct path to the power source.<\/p>\n

Also, in trying to think about the circuit, where the potentiometer as a variable resistor, as opposed to the constant resistor, I bypassed the micro controller and wired the resistors in series to power an LED, so that the variable resistor controls the current going into the constant resistor, which then keeps the current low enough to be good to the LED. . . so its the same effect without the microcontroller.<\/p>\n

[wpvideo JmId03RV]<\/p>\n

The following variable resistor lab is described as a voltage divider, which I am trying to understand using my electronics book.<\/p>\n

\"\"<\/a><\/p>\n

A voltage divider means that the two resistors are set up in series. When resistors are set up in parallel the current is divided and the voltage remains constant. The voltage drop across each resistor \u00a0in series (here one constant and one variable) is directly proportional to the resistance. It is the ratio of resistances between the two resistors that determines the voltage drop distribution. With a variable resistor, as the resistance drops, the current flowing to the micro controller increases, and it should fluctuate from 0 to 5 Volts I think. The constant resistor should be picked to maintain this range, or a range under 5 Volts, using the Voltage In\/Out equations in the above diagram. Also, resistors have a power rating, that cannot be exceeded by the power they resist and turn into heat, so a resistor with twice the max predicted power loss should be chosen.<\/p>\n

This is one voltage divider (divided by a variable force sensing resistor and a 10k ohm resistor) sending an analog value to ADC to microcontroller to the Red LED.<\/p>\n

[wpvideo A7rJFOoX]<\/p>\n

Then I added the flex sensing resistor to a second voltage divider, and mapped that from 500 to 200, which is a reverse, because otherwise the light was on when the flex sensor was straight.<\/p>\n

[wpvideo aWjfjaVR]<\/p>\n

This time if I bypass the micro controller I think there will be more of a difference, because the mapping feature is providing a nice control for the LEDs. It actually works really well for the force sensor, because the range is pretty much 0 to 1000, but the flex sensor, with a smaller range between 200 and 500 shows up weakly without the arduino code, and I don’t have the option of telling it to reverse the resistor’s effect (to light up when the sensor is bent instead of when its straight) Its really nice for me to get rid of the arduino and see the circuit working.<\/p>\n","protected":false},"excerpt":{"rendered":"

analog input labs<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3,24,1],"tags":[],"class_list":["post-58","post","type-post","status-publish","format-standard","hentry","category-labs","category-physical-computing","category-uncategorized"],"_links":{"self":[{"href":"http:\/\/www.mariarabinovich.com\/blog\/wp-json\/wp\/v2\/posts\/58","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.mariarabinovich.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.mariarabinovich.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.mariarabinovich.com\/blog\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"http:\/\/www.mariarabinovich.com\/blog\/wp-json\/wp\/v2\/comments?post=58"}],"version-history":[{"count":14,"href":"http:\/\/www.mariarabinovich.com\/blog\/wp-json\/wp\/v2\/posts\/58\/revisions"}],"predecessor-version":[{"id":437,"href":"http:\/\/www.mariarabinovich.com\/blog\/wp-json\/wp\/v2\/posts\/58\/revisions\/437"}],"wp:attachment":[{"href":"http:\/\/www.mariarabinovich.com\/blog\/wp-json\/wp\/v2\/media?parent=58"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.mariarabinovich.com\/blog\/wp-json\/wp\/v2\/categories?post=58"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.mariarabinovich.com\/blog\/wp-json\/wp\/v2\/tags?post=58"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}