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1  Using Arduino / General Electronics / Strange potentiometer behaviour on: December 12, 2013, 10:07:10 pm
Hello there everyone,

I am in the process of making a small variable voltage power supply using one of these common little LM2596 reference circuit boards, and a 16v DC power supply. It's a DC/DC step down circuit, that can take in anything up to 42v and output anywhere from 1 - 40v, with the upper limit being about a volt less than the input voltage. I've been using these boards for various purposes for a while, mostly bench supplies, but over time the cheap multiturn potentiometers on the board wear out.

I've had good results by replacing that pot with a larger single turn pot from sparkfun, but the tradeoff with that is that now the whole adjustment threshold for 0 - 40v is squashed into the 270 degrees of the single turn pot. It makes getting fine tuned voltages kind of difficult, and I thought I would be able to get around this by springing for one of these more expensive wirewound Bourns potentiometers. However, I'm getting some really weird behavior out of these pot's when I wire them to the board.

If I use my ohmmeter to check the pots beforand, I can verify that they range from 0 - 10K ohm over ten turns. The same ohmmeter shows the single turn pots go from 0 - 10K over one turn. However, when it's hooked up to the board, I can adjust it like normal about halfway through it's range (going from 0 - 10v), but once I get about halfway through it's range, it starts declining as I turn the dial forward.

If this description makes no sense I can try to make a video, but I'd really like to figure out why these potentiometers are doing this.

Thanks

Michael
2  Using Arduino / General Electronics / Re: Probably making a stupid mistake, but need someone to point it out to me on: March 01, 2013, 02:22:13 pm
Yep, I'm just at work at the moment so once I get home I'll be making a schematic. Any particular recommendations for a software package to do that with? Otherwise I'll go with ExpressSCH.
3  Using Arduino / General Electronics / Re: Probably making a stupid mistake, but need someone to point it out to me on: March 01, 2013, 01:54:44 pm
Um, I must respectfully disagree. I know which pin is the common anode, and which ones are the ground for each respective color. What other information should I know about this? The lights work fine on separately, and when all are set to one specific color, and I can flash one between blue and red and green no problem in quick succession. Is there something I am missing here? Because I don't see how this is relevant when we established much earlier in the thread that my issue is probably due to a lack of current control or lack of forward voltage bias separation between the LED's that I have. Sorry if I'm coming across as rude, I'm just genuinely confused.
4  Using Arduino / General Electronics / Re: Probably making a stupid mistake, but need someone to point it out to me on: March 01, 2013, 11:34:37 am
Quote
However, none of my blue lights turn on, only the red ones.
the only way to make any sense out of this whole thing is to take a single
Led in hand, and play with it until you get the pin connections straightened out.

Then, if I truly believed they had built-in Rs, I would take exactly one Led with the
intent that I might be sacrificing it to the gods of thermodynamics, and apply full
voltage to it, and see if it glowed for an instant and then forever flamed out.

ONLY THEN would I hook up the original ckt shown. Better than blowing up $18 worth
of Leds at square one.

Yeah, I did all that. That's how I know that the LED works at full current on 3.3v, at least the 3.3 volts supplied by my Teensy3. That's also how I know I've for sure got the wiring right for this particular model of LED. I know that I am not going to blow these out at this voltage, and my question is why the blue lights aren't turning on when the red ones are on, not whether or not I'm about to blow up 20 bucks of hardware. I'm not.

However, thank you for the recommendation for the three grounds and resistor on Adafruit. I'll be making a better board today and implement protection and such so that when I'm running it at high voltages they don't burn out.

Looking forward to the OP's schematic being posted on this one.

Oh boy... I'm not very good at schematics, but I'll try. Give me a bit.
5  Using Arduino / General Electronics / Re: Probably making a stupid mistake, but need someone to point it out to me on: February 28, 2013, 08:28:06 pm
I know I've got the wiring right on that board for each respective LED. But that makes a lot of sense actually. Are there any good RGB LED's that you know of that won't have this bias issue?
6  Using Arduino / General Electronics / Re: Probably making a stupid mistake, but need someone to point it out to me on: February 28, 2013, 08:15:38 pm
So you think that the reason this isn't working is because I'm missing current flow control? i'll try building another one tomorrow with resistors on it if that is the case.
7  Using Arduino / General Electronics / Re: Probably making a stupid mistake, but need someone to point it out to me on: February 28, 2013, 08:02:25 pm
In my experience, without a current limiting resistor, LED's simply burn out in a couple of seconds. I was under the impression that these ones didn't burn out when I applied 3.3v because they had a built in resistor to the LED. I can't remember who I heard that from, but looking back it's not too plausible. That being said, I'm not sure if that is what is causing the issue because I can run all 9 LED's at full brightness no problem on red but as soon as I throw one blue in the mix, it won't work.
8  Using Arduino / General Electronics / Re: Probably making a stupid mistake, but need someone to point it out to me on: February 28, 2013, 07:53:08 pm
Where are teh current limiting resistors? Are you accounting for the difference in forward voltage between the different colors of LED's?

Built in, and no, I have no idea what that means. Care to elaborate?

This is the LED I'm using

http://www.adafruit.com/products/314
9  Using Arduino / General Electronics / Probably making a stupid mistake, but need someone to point it out to me on: February 28, 2013, 07:15:19 pm
Hey there everyone, I'm trying to set up a 3x3 grid of multicolored LED's that have two sets of jumper banks that I want to use to be able to change the color of each LED. I'm not interested in changing the design unless it's inherent to my issue, so please nobody recommend charlieplexing it. However, I am seeing a strange behaviour out of the board I have made which follows this schematic:



The LED I am using is a knockoff Cree common anode RGB LED.

Basically, I set up my jumpers like this to make five of the LED's go red and four of the LED's go blue.



However, none of my blue lights turn on, only the red ones. But, if I take all of the jumpers out of the red bank, then all of the blue lights will turn on. As soon as even one jumper is bridging the the red grounds, none of the blue grounds will work. Any idea's why this might be?

Thanks

Michael
10  Using Arduino / Networking, Protocols, and Devices / My i2c MCP23017 i/o expander is not working on: December 30, 2012, 03:15:55 pm
As a christmas present I bought myself some MCP23017's (among other things) but I can't get it working. I am new to i2c in general; so i am probably making a simple mistake. I have been following this tutorial over at tronixstuff

Here is a picture of my wiring; since this picture was taken I've added two pull up resistors (2.2o) from both SDA and SCL to the reset pin which is tied to 5v. As well I have ensured that the LED works.


As well, this is the code which I am running on my Teensy2:
Code:
#include <Wire.h>

void setup(){
  Wire.begin();
  delay(100);
  Wire.beginTransmission(0x20);
  Wire.write(0x00);
  Wire.write(0x00);
  Wire.endTransmission();
  delay(100);
  Wire.beginTransmission(0x20);
  Wire.write(0x12);
  Wire.write(11111111);
  Wire.endTransmission();
}

void loop(){
   
}

So any idea's? I'm pretty stuck here. Thanks!

Michael
11  Using Arduino / Project Guidance / Re: Why are all of these buttons acting like they are the same? on: November 04, 2012, 11:05:04 pm
Yes you have improperly followed my instructions (trice times!).

Yeah; great. Thanks. Sorry if my small brain had a hard time comprehending.

It's hard to be sure from the picture, but it looks to me as if you have the resistors wired in series in the line between the switch and the Arduino input. That is not the correct way to wire up pull-up (or pull-down) resistors.

Thanks, I'll rewire and try tomorrow.
12  Using Arduino / Project Guidance / Re: Why are all of these buttons acting like they are the same? on: November 04, 2012, 07:56:20 pm
By gate pin I just meant the pin that is not connected to power.

So I implemented this solution with 10k resistors and I'm still having the same problem. To try to isolate the problem I made a breadboard circuit using similar buttons in the manner you described. Here is a picture of it.



Anyways, the issue is still happening. I will press a button that is not connected to the line that I am reading and get a HIGH. Using the digitalReadSerial example function I read pin 3 and can get HIGH's from most, if not all of the buttons. I am not sure why this is happening but I don't think it is a floating input error unless I've put my resistors on the wrong side.

Anyways, thanks for the help so far. Hopefully we can figure this out

Michael
13  Using Arduino / Project Guidance / Re: Why are all of these buttons acting like they are the same? on: November 03, 2012, 08:12:26 pm
Ok, I didn't think about it that way. So really this is as much a floating input issue as it is a button debouncing problem, because the bounce is returning down to the power board causing noise. That makes a lot more sense now. I'll add resistors to the gate pins on each of my buttons and hopefully that will get it to work.
14  Using Arduino / Project Guidance / Re: Why are all of these buttons acting like they are the same? on: November 03, 2012, 07:56:21 pm
No, it really doesn't. My issue isn't that I'm getting an input that is randomly floating between LOW and HIGH while I'm not pressing a button, it's that when I press any button, even the ones that I'm not reading the lines of; I get a HIGH. So basically all of my buttons are acting like they are wired to the same pin, but really the only common thing they share is a power source.

As well, I'm NOT using the standard four post buttons of which I am used to, I am using panel mounted two post buttons, that don't have positive/negative/signal posts; rather a source and a gate. So in that case; where am I putting the resistor? And is that even my problem at hand here?
15  Using Arduino / Project Guidance / Re: Why are all of these buttons acting like they are the same? on: November 03, 2012, 05:10:30 pm
Here is a diagram of the way that these buttons are wired. The 'Power' board is just a piece of perfboard with every pad connected to the same rail.



The code is inconsequential in this case, I'm just reading pin1 and echoing it to serial in a loop. But here you go anyways

Code:
/*
  DigitalReadSerial
 Reads a digital input on pin 2, prints the result to the serial monitor
 
 This example code is in the public domain.
 */

// digital pin 2 has a pushbutton attached to it. Give it a name:
int pushButton = 1;

// the setup routine runs once when you press reset:
void setup() {
  // initialize serial communication at 9600 bits per second:
  Serial.begin(9600);
  // make the pushbutton's pin an input:
  pinMode(pushButton, INPUT);
}

// the loop routine runs over and over again forever:
void loop() {
  // read the input pin:
  int buttonState = digitalRead(pushButton);
  // print out the state of the button:
  Serial.println(buttonState);
  delay(1);        // delay in between reads for stability
}



If you have any questions then feel free. But I would like to hear thoughts towards needing resistors on the buttons as was discussed earlier.
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