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1  Using Arduino / General Electronics / Re: It works!! Even when others said it wouldn't. on: May 09, 2012, 07:10:32 pm
I posted a circuit awhile back and a number of people said it would never work.  Well because so many implied that I was crazy or worse I went ahead and built the circuit.
There seems to be a number of people that want to insult and degrade people.  So for those just ignore them.  If someone wants to help you, or you want to help, those are the people you need to associate with.  Remember you can always build the circuit and see for yourself.

It would have been nice if you had simply updated your subject
http://arduino.cc/forum/index.php/topic,103413.0.html

You are emotionally over-invested in your "design".
Start drawing some current from that, from both "outputs" -- at the same time.



I didn't update the original thread because I didn't want to rub your nose in your error.  But you just did it yourself.

I never said this was my design.  Actually I said I found it on line so it's difficult to make the point that I am "over-invested" in it.  What I am invested it is something I have seen many times on this forum.  The negativity and degrading comments to others.  I think that is just plain wrong.  Now I am not pointing the finger at you but you didn't have anything to offer except negativity in the original post.  The first comment you made was totally unhelpful and very negative.  If that's how you want to live your life I will just ignore your posts in the future.  But I would hope that you want to be a good person and help others not try and degrade them.
2  Using Arduino / General Electronics / Re: It works!! Even when others said it wouldn't. on: May 09, 2012, 07:01:39 pm
Do the voltages hold when you start drawing current? That's the real test.

I didn't want to put any load on it until it had some heat sinks on it.  And I wanted to flush out the circuit with some caps.  But I am sure it will work.
3  Using Arduino / General Electronics / Re: Teaching myself electrical engineering. on: May 09, 2012, 06:54:22 pm
I am in the same situation.  I have a CS degree, a worthless  scrap of paper these days.  We homeschool and I wanted to do something with my son.  I did the same thing you are doing.  Reading books to find the information.  It's of little value compared with just building stuff.  One of the books I did read and thought it had some value, but only in the first half of the book was:
"Electrical Engineering 101, everything you should have learned in school but probably didn't." By Darren Ashby.
Here is an amazon link:
http://www.amazon.com/Electrical-Engineering-101-Third-Edition/dp/0123860016/ref=sr_1_1?s=books&ie=UTF8&qid=1336605168&sr=1-1

After you read the first half of that book just start making things.  Kits are OK but they don't teach much beyond soldering skills. 

Learn about series and parallel circuits with resistors and capacitors.  Then checkout youtube for more tutorials then you want to watch.  But there are good ones and not so good ones.  For fun I watch Dave Jones' EEVBlog on youtube.

After the few actual books you need it's more important to have good equipment.  Get a good soldering station.  I bought a Hakko fx-888 and I couldn't believe how much easier it was to do good soldering.   I also bought an electric skillet to do surface mount work.  I mounted some hall effect sensors to breakout boards with it and it worked great.  But for fun I bought a hot air rework station for $62 delivered from Ebay.  I only just got it and have only used it for heat shrink tube.  But Dave Jones did a review of the same model and he likes it. One bit of kit I have that is more fun then useful but it is very useful is an oscilloscope.  I bought the Rigol DS1102E for $399.  It used to be about $800 but some people figured out how to hack the firmware on Rigols cheap scope.  So Rigol cut the price of this one in half.  I got mine from  http://www.saelig.com.

I have gotten a lot of stuff from BGMicro.  They are cheap enough that you can blow up a few items and still be ahead.  And don't forget that a lot of companies give out free samples.  I asked Maxim for 4 50 watt class D amps and they sent them to me for free and no shipping.  If I had bought them from digikey it would have been close to fifty bucks.

So good luck it's not hard you just have to keep at it.  If you can write modular software you can make modular circuits.  It's the same principle.
4  Using Arduino / General Electronics / Re: Can you get a negative and positive voltage out of the same source? on: May 09, 2012, 05:55:23 pm
Yes there is and it's very simple.  You need a couple of regulators, lm7809 and lm7909, and a voltage source that is higher then the drop out of the regulators. The dropout voltage of the 7809 and 7909 is about 2 volts.  So you need at least 11 volts but more is better up to a point.  Extra power is released as heat and the max these regulators will go is 35 volts.  Here is a link to a thread I posted showing how this is done:

http://arduino.cc/forum/index.php/topic,105208.0.html

The circuit in the above thread is minimal.  You should consider looking at the data sheet and it will show you how put caps in the circuit.
5  Using Arduino / General Electronics / It works!! Even when others said it wouldn't. on: May 09, 2012, 05:45:49 pm
I posted a circuit awhile back and a number of people said it would never work.  Well because so many implied that I was crazy or worse I went ahead and built the circuit.  Here is the schematic I originally posted:




Now I don't have a 24 volt source but I do have an 18 volt source.  Also I only had 7809 and 7909 regulators not the 7815 and the 7915 in the schematic but the concept is the same.  Here is the circuit working.



The gray meter in the back is the supply voltage.  The meters in the front shows the output of the 7809 regulator and the output of the 7909 regulator (the 7909 is the negative value). Now I probably should throw some caps at the circuit but this shows it works.

So my point here is don't believe the nay sayers.  There seems to be a number of people that want to insult and degrade people.  So for those just ignore them.  If someone wants to help you, or you want to help, those are the people you need to associate with.  Remember you can always build the circuit and see for yourself.
6  Using Arduino / Installation & Troubleshooting / Re: I think I found a bug in arduino. on: May 06, 2012, 09:55:29 pm
Well I thought by including the link from the page I cut the code from it would be clear that it wasn't my code but an idea as to how to work around the problem.

If what James wrote is true then the ISR is NOT stored in flash memory or in sram ( I actually suspected this).  ISR code has to be in EEPROM memory.  It's the only way for what I am talking about to happen.  So walking the EEPROM memory is the way to work around this problem. 

Anybody can try this themselves.  Use one arduino to toggle a pin on and off, say once a second, like the blink sketch.  Then connect a jumper from the pin you used on one board, pin 13 if it's the blink sketch, and connect it to pin 2 on a different board.  This will be external interrupt 0.  Write and ISR to output to the serial port some debug statement when the interrupt fires.  Check this code works and the debuging serial output is there. 

This installs the code for the ISR.  Then write a different sketch that does something without an ISR, like the blink sketch for example.  Then upload the new sketch to the board that had the ISR on it.  While the blink sketch is running toggle pin 2 to fire off the old ISR code and check the serial monitor to see it output code that is not in the sketch that is running.

I'm sure that everybody reading this has more then one arduino board and that's all you need to see this happen.

7  Using Arduino / Installation & Troubleshooting / Re: I think I found a bug in arduino. on: May 06, 2012, 02:54:17 pm
Yes it is repeatable.  The board is an UNO R3.  As far as I know that is the most resent.  But the problem is not in the board but in the uploader.  It should wipe all memory and then load the sketch.  That is not happening.  As far as I can tell it is just writing the new code to the memory on the board.

I suspect there is a work around for this problem but I haven't had the time to test it.  There are a couple of examples on line to check the amount of memory and to clear the memory in the eeprom.  Here is a link to the page that shows how to check the memory:
http://arduino.cc/playground/Code/AvailableMemory
And here is the code from that page:
Code:
/* This function places the current value of the heap and stack pointers in the
 * variables. You can call it from any place in your code and save the data for
 * outputting or displaying later. This allows you to check at different parts of
 * your program flow.
 * The stack pointer starts at the top of RAM and grows downwards. The heap pointer
 * starts just above the static variables etc. and grows upwards. SP should always
 * be larger than HP or you'll be in big trouble! The smaller the gap, the more
 * careful you need to be. Julian Gall 6-Feb-2009.
 */
uint8_t * heapptr, * stackptr;
void check_mem() {
  stackptr = (uint8_t *)malloc(4);          // use stackptr temporarily
  heapptr = stackptr;                     // save value of heap pointer
  free(stackptr);      // free up the memory again (sets stackptr to 0)
  stackptr =  (uint8_t *)(SP);           // save value of stack pointer
}

Notice in this function malloc() is called.  If this is changed to calloc() it will clear the memory at the same time as it is allocated.  Then one just frees the memory and you are good to go.  Then there is this code to clear the EEPROM found here:http://arduino.cc/en/Tutorial/EEPROMClear 
and here is the code from that page:
Code:
/*
 * EEPROM Clear
 *
 * Sets all of the bytes of the EEPROM to 0.
 * This example code is in the public domain.

 */

#include <EEPROM.h>

void setup()
{
  // write a 0 to all 512 bytes of the EEPROM
  for (int i = 0; i < 512; i++)
    EEPROM.write(i, 0);
   
  // turn the LED on when we're done
  digitalWrite(13, HIGH);
}

Notice that in the EEPROM code 512 is hard coded in.  I think that is bad style.  There needs to be a header file that lists the size of the EEPROM by processor type.  So one could use something like SEEPROM_168 or SEEPROM_328P and these would equate to 512 and 1024 respectively.  And so on for other processors. 


Also I don't have much time on micros.  I do have a lot of experience on PCs but it was a long time ago.   I have no idea if calloc() is supported on the micro platform.  If this really is GNU C under the covers it should but don't shoot me if it doesn't.

8  Using Arduino / Installation & Troubleshooting / I think I found a bug in arduino. on: May 06, 2012, 12:01:39 am
I wrote a sketch that has an external interrupt handler on pin 2 interrupt 0.  This worked fine.  I have 5 volts hitting pin 2 to fire the ISP. I had some debugging info output to the serial port in the ISR. This worked no problem.  I then uploaded a completely different sketch that has no ISR.  What a surprise when I was running the new sketch and the debugging info from the old sketch ISR came out the serial port.  I did have the circuit that hit pin 2 with five volts connected but I was running a different sketch with no ISR.  This means that arduino does not wipe the memory when it uploads a new sketch.  So if the new sketch does not overwrite the old it still is there.  I suspect it's only true for ISRs but to have code run from a different sketch then what is currently running is a bug. How should this be handled?

9  Using Arduino / General Electronics / Re: I have a problem with the numbers.. Unusual for me. on: April 27, 2012, 07:44:46 pm
Sorry, joseph_m, but that circuit, as drawn, is dead in the water.

Well that's helpful.  Want to elaborate on that?  It came right out of the data sheet.
10  Using Arduino / General Electronics / Re: I have a problem with the numbers.. Unusual for me. on: April 27, 2012, 07:43:20 pm
Run the number with Vset at -5 volts and that is what you want Vout to be and you get zero for your resistance of R1.  Run the numbers you will see what I mean.
11  Using Arduino / General Electronics / Re: Power Supply and Connection with the Power plug available in Arduino Board on: April 27, 2012, 07:41:18 pm
Just hook up a 9 volt battery to a 2.1mm power jack.
Internally these batteries are built from 6 miniature 1.5V cells connected in series and they're designed for long term use in ultra low power devices. They are popular because of form factor and availability, but not a good choice for a microcontroller project. Due to the limited current capacity and the higher than desired voltage (9V as opposed to 5V or 3V3) they are extremely inefficient as a power source for Arduino. Using a 9V battery for test when nothing else is available is one thing, but designing for it is just silly.

Maybe you didn't read the OP's remark about his desire to run his Arduino from batteries.  So you don't think that running an arduino off a 9-volt is not a good idea.

I am not sure about the use of a 9 volt not working. I did a quick google search on how much an arduino draws.  The result I got was 18.7mA.  And I found that an   Alkaline 9volt batt has 565 mAh and a lithium has 1200 mAh.  So you can expect to get something like 30 to 65 hours of use.  Now if you are sourcing current out of the pins it will be much less.  But that goes to what I said about getting a wall wort.  But it really depends on the usage as to how "silly" it is to run your arduino off of a battery.  If you are going to run your arduino for a couple of hours and then shut it down it's not silly at all.  And if you are building a circuit that will run say in your fishing boat it's not silly at all.  There are far to many unknowns to say it's silly.

12  Using Arduino / General Electronics / I have a problem with the numbers.. Unusual for me. on: April 27, 2012, 07:10:16 pm
I am building a bench supply.  I have a 36 volt 9 amp supply that I was going to use as a voltage source.  But it doesn't have negative voltage.  I came across this circuit for creating negative voltage:


So that's good.  I can use fixed voltage regulators for many voltages but it would be nice to have an adjustable voltage as well.  So I am looking at this from a data sheet for the  LM79xx:
Here is the link to the data sheet:http://www.hep.upenn.edu/SNO/daq/parts/lm7915.pdf
and this is the part I am having some difficulty with:


Look at the bottom of the page.  There is a set of values for R2 at different voltages.  Using these values I need to find R1 but the numbers I am getting are impossible.  So I suspect I don't grok what Vset is and the only place you will find Vset in the data sheet is right there.  I am using 36 volts for the supply, that is what I thought Vset would be, and I want a negative 15 volts out.  How is this done?  I keep coming up with a negative value for R1 and unless things have changed a lot I don't think you can get a negative resistance potentiometer.
13  Using Arduino / General Electronics / Re: Leakage current in a driver IC; how to compensate? on: April 27, 2012, 04:29:08 pm
I don't think the resistor is the correct item to control the 70 volt problem.  I would use a transistor to turn on the lights.  Just wire up the transistor as a switch.  The ground of the Nixie has no voltage until the light is lit.  Use this ground voltage of the nixie to turn on, or open, the transistor to the other light.  Then when the nixies are off all lights will be off.  And when the nixies are on there is voltage going to ground that turns on the transistor and the other lights turn on.  I hope that is clear enough.  Lets see if I can do some ascii art here.

Nixie ground pin
0------|-----------------------ground
        |
        |----------------------base of transistor

Figure out the rest.


Now I have never worked with nixie tubes.  So there might be enough voltage flowing to ground when they are off to open the transistor.  I just don't know.  But a little work with a VOM will tell you if this idea will work.
14  Using Arduino / General Electronics / Re: real music (not tones) on: April 27, 2012, 04:03:29 pm
Everybody gave you good advice but if you want to learn about sound reproduction you might want to start with studying amplifiers. In particular the class D amp.  It is most applicable for use with the arduino.  If you see the class D amp and a motor control using an H-bridge you will see that they are pretty much the same except there is a speaker where the motor would be.  When I first noticed that I thought it was amazing.
15  Using Arduino / General Electronics / Re: Power Supply and Connection with the Power plug available in Arduino Board on: April 27, 2012, 03:30:33 pm
All the answers will work but in my opinion they are overly complicated.  Just hook up a 9 volt battery to a 2.1mm power jack.  You can get both the 9volt batt connector and the  2.1mm power jack at radio shack. Or you can order them from Jameco or Digikey or where ever.  Wire the center positive on the power jack and plug it in.  You're done.  Now if you want something that draws power from the mains and plugs into the board get a wall wort from radio shack or jameco or where ever and you are done. 

I actually keep a supply of wall worts just for this purpose. As they teach in the Boy Sprouts "always be prepared to start a fire anywhere."
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