Gsyfuy

A newer friend of my brother's gave him a load of baseball cards that are supposedly extremely valuable. Is this a scam?

Accidentally leaked the solution to an assignment, what to do now? (I'm the prof)

How do you conduct xenoanthropology after first contact?

The use of multiple foreign keys on same column in SQL Server

I’m planning on buying a laser printer but concerned about the life cycle of toner in the machine

How can I fix this gap between bookcases I made?

whey we use polarized capacitor?

How to type dʒ symbol (IPA) on Mac?

What makes Graph invariants so useful/important?

How does one intimidate enemies without having the capacity for violence?

Is it possible to make sharp wind that can cut stuff from afar?

Concept of linear mappings are confusing me

What is the command to reset a PC without deleting any files

Is there really no realistic way for a skeleton monster to move around without magic?

LED on same Pin as Toggle Switch, not illuminating

What typically incentivizes a professor to change jobs to a lower ranking university?

Copenhagen passport control - US citizen

How do we improve the relationship with a client software team that performs poorly and is becoming less collaborative?

Why is the design of haulage companies so “special”?

What is the meaning of "of trouble" in the following sentence?

Can an x86 CPU running in real mode be considered to be basically an 8086 CPU?

What Brexit solution does the DUP want?

"which" command doesn't work / path of Safari?

Shell script can be run only with sh command

LED on same Pin as Toggle Switch, not illuminating

how to calculate correct resistor value to use with LEDs Potentiometer and other devices?Source power with 2 V and LED with forward voltage of 2 V7-Segment Common AnodeConnecting a switch and a MOSFET to an Arduino?Multi-LED Toggle SwitchWhy adding a LED between Pin 3 and Ground causes LCD display not to show text?Getting more current through an LED arraydigitalRead not reading input pin of ESP8266-01Yellow LED got burned, green LED didn'tProblem : Trigger limit switch to stop DC motor

0

I am trying to do something I think should be relatively simple. I would like to read an input from a toggle switch, and have a red 5mm LED indicate the state of the switch. Rather, however, than have an input for the switch and an output for the LED (controlled by software), I'd like to put them in series on a single circuit. That is, flip the toggle and current flows from the 5v source on the Arduino Uno through an LED and to an input pin on the Arduino. (I would ultimately like to have eight such switches; I am trying to create a sort of simulated byte, with individually flippable bits controlled by toggles; this will be read by a GTK Python program, that can interpret that "byte" in different ways: as a decimal value, a hex value, an ASCII character, a color in 8-bit color space, etc).

So, I have an LED with a 200 Ohm current-limiting resistor. I also have a pull-down resistor (1k) to prevent the toggle from floating.

My results, however, have been inconsistent. Using a breadboard, I've gotten this working. But it seems very fragile, and sometimes when I rebuild the circuit on a breadboard, it doesn't work as expected. Right now, for instance, the switch seems to work, and I am reading the expected value from the Serial Monitor--but the LED is not illuminating.

I had been playing around with different values for the pull-down resistor and the current-limiting resistor. This pair (200-ohm current limiting; 1k pull down) seemed to work, but now isn't. (I have swapped out the LED; and current is passing through the LED, otherwise I wouldn't be able to read the correct pin value--I think.)

Is there something I'm not understanding? Does the position of the current limiting resistor (before/after the LED) make any difference (I assume not)? Does this seem like the correct setup for what I'm trying to achieve? More generally, should, in principle, this approach scale to 8 more toggle/LED pairs? Is there a better/smarter approach? Is there a reason why I see so few Arduino projects that put LEDs in series with an input toggle?

The breadboard looks like this:

arduino-uno led switch

share|improve this question

asked 7 hours ago

cforstercforster

1033

New contributor

cforster is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Do you want to turn the led on and off regardless of the switch as well? Or do you only want to read the switch (and the switch turns the led on and off).
  
  – Jot
  3 hours ago
  

  
  
  
  

add a comment | 

0

I am trying to do something I think should be relatively simple. I would like to read an input from a toggle switch, and have a red 5mm LED indicate the state of the switch. Rather, however, than have an input for the switch and an output for the LED (controlled by software), I'd like to put them in series on a single circuit. That is, flip the toggle and current flows from the 5v source on the Arduino Uno through an LED and to an input pin on the Arduino. (I would ultimately like to have eight such switches; I am trying to create a sort of simulated byte, with individually flippable bits controlled by toggles; this will be read by a GTK Python program, that can interpret that "byte" in different ways: as a decimal value, a hex value, an ASCII character, a color in 8-bit color space, etc).

So, I have an LED with a 200 Ohm current-limiting resistor. I also have a pull-down resistor (1k) to prevent the toggle from floating.

My results, however, have been inconsistent. Using a breadboard, I've gotten this working. But it seems very fragile, and sometimes when I rebuild the circuit on a breadboard, it doesn't work as expected. Right now, for instance, the switch seems to work, and I am reading the expected value from the Serial Monitor--but the LED is not illuminating.

I had been playing around with different values for the pull-down resistor and the current-limiting resistor. This pair (200-ohm current limiting; 1k pull down) seemed to work, but now isn't. (I have swapped out the LED; and current is passing through the LED, otherwise I wouldn't be able to read the correct pin value--I think.)

Is there something I'm not understanding? Does the position of the current limiting resistor (before/after the LED) make any difference (I assume not)? Does this seem like the correct setup for what I'm trying to achieve? More generally, should, in principle, this approach scale to 8 more toggle/LED pairs? Is there a better/smarter approach? Is there a reason why I see so few Arduino projects that put LEDs in series with an input toggle?

The breadboard looks like this:

arduino-uno led switch

share|improve this question

asked 7 hours ago

cforstercforster

1033

New contributor

cforster is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Do you want to turn the led on and off regardless of the switch as well? Or do you only want to read the switch (and the switch turns the led on and off).
  
  – Jot
  3 hours ago
  

  
  
  
  

add a comment | 

I am trying to do something I think should be relatively simple. I would like to read an input from a toggle switch, and have a red 5mm LED indicate the state of the switch. Rather, however, than have an input for the switch and an output for the LED (controlled by software), I'd like to put them in series on a single circuit. That is, flip the toggle and current flows from the 5v source on the Arduino Uno through an LED and to an input pin on the Arduino. (I would ultimately like to have eight such switches; I am trying to create a sort of simulated byte, with individually flippable bits controlled by toggles; this will be read by a GTK Python program, that can interpret that "byte" in different ways: as a decimal value, a hex value, an ASCII character, a color in 8-bit color space, etc).

So, I have an LED with a 200 Ohm current-limiting resistor. I also have a pull-down resistor (1k) to prevent the toggle from floating.

My results, however, have been inconsistent. Using a breadboard, I've gotten this working. But it seems very fragile, and sometimes when I rebuild the circuit on a breadboard, it doesn't work as expected. Right now, for instance, the switch seems to work, and I am reading the expected value from the Serial Monitor--but the LED is not illuminating.

I had been playing around with different values for the pull-down resistor and the current-limiting resistor. This pair (200-ohm current limiting; 1k pull down) seemed to work, but now isn't. (I have swapped out the LED; and current is passing through the LED, otherwise I wouldn't be able to read the correct pin value--I think.)

Is there something I'm not understanding? Does the position of the current limiting resistor (before/after the LED) make any difference (I assume not)? Does this seem like the correct setup for what I'm trying to achieve? More generally, should, in principle, this approach scale to 8 more toggle/LED pairs? Is there a better/smarter approach? Is there a reason why I see so few Arduino projects that put LEDs in series with an input toggle?

The breadboard looks like this:

arduino-uno led switch

share|improve this question

asked 7 hours ago

cforstercforster

1033

New contributor

cforster is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

asked 7 hours ago

cforstercforster

1033

New contributor

cforster is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

asked 7 hours ago

cforstercforster

1033

New contributor

cforster is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 7 hours ago

cforstercforster

1033

New contributor

cforster is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 7 hours ago

cforstercforster

1033

1 Answer
1

active

oldest

votes

3

LEDs have a (fairly) fixed voltage drop across them. The red LED is about 2V.

You can use that to work out the voltage at the input. You basically have a voltage divider, with your 200Ω resistor as R1, and your 1kΩ resistor as R2. The voltage drop of the diode is subtracted from Vin.

So:

Vout = (Vin - Vled) * (R2 / (R1 + R2))



     = (5 - 2) * (1000 / (200 + 1000))



     = 3 * (1000 / 1200) 



     = 3 * 0.833



     = 2.5V

The ATMega328P datasheet states that a HIGH input voltage must be over 0.6*Vcc, and a LOW input voltage must be below 0.3*Vcc. That means to register a HIGH you need more than 3V. To register a LOW you need less than 1.5V.

You're between those two voltages - in the "dead zone".

The simplest way to achieve what you want is to use a douple-pole switch and keep the LED completely separate from the Arduino.

share|improve this answer

answered 6 hours ago

Majenko♦Majenko

69.4k43277

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Using a double-pole switch seems indeed the smarter approach here. Thanks. I see your logic... but it doesn't account for my case, however, where I am getting the correct input on the Arduino--the LED is not illuminating. The dead zone you note would be like a floating pin, no?
  
  – cforster
  22 mins ago
  

  
  
  
  

add a comment | 

Your Answer

StackExchange.ifUsing("editor", function () {
return StackExchange.using("schematics", function () {
StackExchange.schematics.init();
});
}, "cicuitlab");

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "540"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});


}
});

cforster is a new contributor. Be nice, and check out our Code of Conduct.

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name

Email

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2farduino.stackexchange.com%2fquestions%2f63273%2fled-on-same-pin-as-toggle-switch-not-illuminating%23new-answer', 'question_page');
}
);

Post as a guest

Name

Email

Required, but never shown

3

LEDs have a (fairly) fixed voltage drop across them. The red LED is about 2V.

You can use that to work out the voltage at the input. You basically have a voltage divider, with your 200Ω resistor as R1, and your 1kΩ resistor as R2. The voltage drop of the diode is subtracted from Vin.

So:

Vout = (Vin - Vled) * (R2 / (R1 + R2))



     = (5 - 2) * (1000 / (200 + 1000))



     = 3 * (1000 / 1200) 



     = 3 * 0.833



     = 2.5V

The ATMega328P datasheet states that a HIGH input voltage must be over 0.6*Vcc, and a LOW input voltage must be below 0.3*Vcc. That means to register a HIGH you need more than 3V. To register a LOW you need less than 1.5V.

You're between those two voltages - in the "dead zone".

The simplest way to achieve what you want is to use a douple-pole switch and keep the LED completely separate from the Arduino.

share|improve this answer

answered 6 hours ago

Majenko♦Majenko

69.4k43277

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Using a double-pole switch seems indeed the smarter approach here. Thanks. I see your logic... but it doesn't account for my case, however, where I am getting the correct input on the Arduino--the LED is not illuminating. The dead zone you note would be like a floating pin, no?
  
  – cforster
  22 mins ago
  

  
  
  
  

add a comment | 

3

LEDs have a (fairly) fixed voltage drop across them. The red LED is about 2V.

You can use that to work out the voltage at the input. You basically have a voltage divider, with your 200Ω resistor as R1, and your 1kΩ resistor as R2. The voltage drop of the diode is subtracted from Vin.

So:

Vout = (Vin - Vled) * (R2 / (R1 + R2))



     = (5 - 2) * (1000 / (200 + 1000))



     = 3 * (1000 / 1200) 



     = 3 * 0.833



     = 2.5V

The ATMega328P datasheet states that a HIGH input voltage must be over 0.6*Vcc, and a LOW input voltage must be below 0.3*Vcc. That means to register a HIGH you need more than 3V. To register a LOW you need less than 1.5V.

You're between those two voltages - in the "dead zone".

The simplest way to achieve what you want is to use a douple-pole switch and keep the LED completely separate from the Arduino.

share|improve this answer

answered 6 hours ago

Majenko♦Majenko

69.4k43277

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Using a double-pole switch seems indeed the smarter approach here. Thanks. I see your logic... but it doesn't account for my case, however, where I am getting the correct input on the Arduino--the LED is not illuminating. The dead zone you note would be like a floating pin, no?
  
  – cforster
  22 mins ago
  

  
  
  
  

add a comment | 

LEDs have a (fairly) fixed voltage drop across them. The red LED is about 2V.

You can use that to work out the voltage at the input. You basically have a voltage divider, with your 200Ω resistor as R1, and your 1kΩ resistor as R2. The voltage drop of the diode is subtracted from Vin.

So:

Vout = (Vin - Vled) * (R2 / (R1 + R2))



     = (5 - 2) * (1000 / (200 + 1000))



     = 3 * (1000 / 1200) 



     = 3 * 0.833



     = 2.5V

The ATMega328P datasheet states that a HIGH input voltage must be over 0.6*Vcc, and a LOW input voltage must be below 0.3*Vcc. That means to register a HIGH you need more than 3V. To register a LOW you need less than 1.5V.

You're between those two voltages - in the "dead zone".

The simplest way to achieve what you want is to use a douple-pole switch and keep the LED completely separate from the Arduino.

share|improve this answer

answered 6 hours ago

Majenko♦Majenko

69.4k43277

Vout = (Vin - Vled) * (R2 / (R1 + R2))



     = (5 - 2) * (1000 / (200 + 1000))



     = 3 * (1000 / 1200) 



     = 3 * 0.833



     = 2.5V

share|improve this answer

answered 6 hours ago

Majenko♦Majenko

69.4k43277

answered 6 hours ago

Majenko♦Majenko

69.4k43277

answered 6 hours ago

Majenko♦Majenko

69.4k43277