I saw some circuit diagrams that didn't use the capacitors (as opposed to some that did).  I figured they were just for smoothing the voltage and weren't a hard requirement.

Obviously I was wrong :-)

Thanks for everyone's help.

I rebuilt my LM317 circuit and it works - must have done something wrong before?  The only difference this time is I included the capacitors.

Off to buy some heatsinks now as my LM317 is running super hot.

Thanks again.

I tried the regulator at both ends - but even on an ultra short cable run of 20cm the voltage still drops to 2.2v.  The only thing I didn't use were the capacitors in the circuit - I'll add them in, but I don't see them making any difference.

I tried using a thicker cable and running direct from the 5v on the PSU - this improved the system - the voltage dropped to about 4.5v instead of 4.2v on the thinner cable.  The camera was able to power up, but kept rebooting itself (so I presume 4.5v is not quite enough power).  I could try thicker cable again, but we're starting to talk more money... :-(

Very keen to get the voltage regulator working with the 12v supply on the thinner cable (not to mention the cable is already run through conduit so changing it will be a pain).

Thanks for all the info - but here is one more problem...

I picked up a LM317 voltage regulator.   Can successfully drop the voltage from 12 to 5.   However, using a short cable run of about 20cm, as soon as I plug in the camera, the voltage drops from 5v to about 2.2v.

Not sure what is going on here??  If I plug straight into the 5v output of the PSU using the same 20cm cable run, it works perfectly.  Why does my voltage keep dropping to 2.2v whenever I have some circuitry in place?

Thanks.  I'll give that a go.

Hi all.  I need some help please.  I have an IP Camera that runs off a 5v 1500ma supply.  I'm installing these cameras and running the power back to a central location.  Here's what I'm doing:

From the power source to the camera is approximately 25 metres.

First, I just cut the plug from the supply and re-terminated at each end of the 25m run.  My problem is the 5v drops to about 1.5v over the 25m which is not enough to power the camera
Second, I grabbed an old PC PSU and used the 5v supply.  There was no voltage drop until I plugged the camera in.  It dropped to about 4.2v which was not enough to power the camera
Third, using the 12v supply from the PSU - no voltage drop until plugging in the camera - it drops to about 7v - this fried the camera after a few minutes.
Fourth, using the 12v supply and a simple voltage divider circuit with 2 resistors I halved the voltage to 6v.  When I plug in the camera the voltage drops to 2.2v - not enough to work.  Doesn't matter which value resistors I use, the voltage still drops to 2.2v when I plug in the camera.  I tried the voltage divider at the power source end and the camera end.  Same result.
Fifth, using the 12v supply and a voltage divider circuit, tried dropping the voltage to various levels (10v and 7v) - but the voltage still drops to about 2.2v when plugging in the camera.

So far, my only solution is to run mains power to the camera and use the power supply that came with it - don't want to do this.

Any help please?

Thanks.

Used a 47k and 67k - works great.  No heat whatsoever.

Thank you!  Didn't even think about power/current.... that's my brain freeze moment of the week.

Hi All,

A project I'm working on I need to measure the charge of a 9V battery.  Essentially it's a voltmeter.

Using the analogue inputs on a Uno (the end project will just be a stand alone ATmega328), I need to scale back the 9V to under 5V.  I was told to use a voltage divider as per this site: http://www.raltron.com/cust/tools/voltage_divider.asp

I used the values 6.8 and 4.7 ohm for the resistor.  According to the calculator on the website this would scale back 12V to 4.9V hence allowing for a way overcharged battery to be connected without damaging the input pins.

However, upon connecting the battery to the resistors (arduino not connected), the 6.8ohm resistor started to smoke and burn.  I'm at work right now and don't want to set off the fire alarms (I'm right next to our major data centre!).

Can anyone advise what I have done wrong? Or what I should be doing?

Thanks,
Ross.

I would definitely use the TLC5940.  I'm currently using 8 of them to control 42 RGB LEDs in a project I'm working on.

http://www.raltron.com/cust/tools/voltage_divider.asp

Perfect.  Thank you.

Hi All,

I've tried searching but can't find anything.  I can use my Arduino to act as a voltmeter for up to 5V - but I need to measure up to 9V batteries.  I obviously can't plug 9V directly to the analogue input pins.

Can anyone point me in the right direction to measuring up to 9V?

Thanks,
Ross.

Thanks for the advice.

I'll modify my code as per your suggestions and give it a try.

PS. I was only using the Serial monitor for debugging - it didn't work without the Serial.print commands either.

But I'll try updating a global and processing it in the loop.  I'll also try to do away with Strings.

Thanks.  Will post again if it works or doesn't.

Hi All,

I'm having some trouble communicating via I2C between 2 ATmega328s.

Here is the setup:

I have 2 ATmega328 chips.  I assign one the address 0x0a and the other 0x0b.

I can send commands from either chip to the other without any problems.  However, what I need to do is when a command is received, the chip needs to send a response.  This is where it falls over.  Through debugging, I can see this is the flow:

0x0b sends command "requestID" to 0x0a
0x0a receives "requestID" and tries to send "id1" back to 0x0b

This is where it stops.  0x0b never receives anything back.  And it seems that 0x0a never sends it.  I can't even get a return code from Wire.endTransmission() on 0x0a - it seems to crash on the endTransmission().

I've tried reversing the roles of each chip to rule out a faulty chip, but I have the same problem.  As mentioned, I can send multiple commands and they are all received OK, but as soon as I try to send a response back after receiving a command it crashes.  I have tried adding in delays between sending and receiving, but no luck.

A4 is connected to A4, and A5 to A5, both chips share the same ground.  These are the only two devices on the bus.  I have tried with and without pullup resistors. Any help?

Here is my code on device 0x0a:

Code:

#include <Wire.h>

String i2cBuffer="";
byte buffer=0x00;
 
void setup() {
  Serial.begin(9600);
  Wire.begin(0x0a);
  Wire.onReceive(receiveEvent);
}

void receiveEvent(int howMany){
  i2cBuffer="";
  while (Wire.available() > 0){
    buffer = Wire.receive();
    i2cBuffer=String(i2cBuffer + buffer);
  }
  processBuffer(i2cBuffer);
}


void processBuffer(String processCommand) {
  Serial.print("Command Received: '");
  Serial.print(processCommand);
  Serial.println("'");
  if (processCommand=="requestID") {
    sendCommand(0x0b,"id1");
  }
}
 
void sendCommand(byte device, String command) {
  char sendChar[32]="";
  command.toCharArray(sendChar,32);
  Serial.print("Sending '");
  Serial.print(command);
  Serial.print("' to Device ");
  Serial.println(device,HEX); 
  Wire.beginTransmission(device);
  Wire.send(sendChar);
  int response=Wire.endTransmission();
  Serial.print("Return Code: ");
  Serial.println(response);       
}


void loop()
{

}

Excellent!  Thanks very much.  Works perfectly.  The I2C documentation on the Arduino website wasn't clear on this.

Thanks again.