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1  Using Arduino / Project Guidance / Re: Amp options for remote apps on: September 17, 2014, 02:13:36 am
You can put a refernce voltage into the AREF pin of your Arduino using a voltage divider (trimpot?).

Set the reference referring to this page.

With such low values you may need to look at some filtering for noise.
2  Using Arduino / Programming Questions / Re: SIM900 programming problems, help needed on: September 13, 2014, 08:52:31 pm
looks like I have to learn  how to use string and find words inside a string to give a command.
Got any good sites?

You will see in the my example code a couple of posts back that I used the strtok() function to do just this.

Have a look at the example and look up the command using google.
3  Using Arduino / Networking, Protocols, and Devices / Re: Arduino and GPS - GSM module on: September 13, 2014, 07:53:03 pm
Have a look at the Simcom SIM908 module (and other models/makes) to see if it suits your providers frequencies.
It (and others) have the GPS integrated into the SMS/phone module at no apparent cost penalty and simplifies your code and connections to your Arduino.
4  Using Arduino / Motors, Mechanics, and Power / Re: controlling DC motor forward on: September 13, 2014, 07:42:08 pm
To send keystrokes in the serial monitor in the IDE you need to click the "Send" button.

You  should try another terminal program like the freeware "Putty" which sends the keystrokes  without you having to press enter or "Send". Just check that the typematic capability keeps sending chars when you hold a key on the keyboard. You will need to constantly check the incoming chars in your sketch to determine when the key is released.
5  Using Arduino / Microcontrollers / Re: Can an Arduino UNO output variable a voltage? on: September 13, 2014, 07:27:50 pm
By using a RC combination you will get a voltage drop across the resistor thereby not getting an accurate input into the LM3914.

What would the effect be of just using the capacitor and no resistor in this application?
6  Using Arduino / Programming Questions / Re: SIM900 programming problems, help needed on: August 19, 2014, 07:29:21 am
Here's a routine that I use to store the sms string from the 900 and break it up into its constituent parts. The message ends up in global vairable called "pumpcommand".  I connect to the 900 at 9600 baud so you may have to adjust the delays (to avoid buffer overflow) as you use 19200. I use  software serial to output debug messages.

boolean CheckSMS()
  int BufferLength = 80;
  char InBuffer[BufferLength];
  InBuffer[0] = '\0'; 
  while(Serial.available() > 0); 
  char temp;
  int i = 0;
  unsigned long startTime = millis();
  while(Serial.available() < 10 && ((millis() - startTime ) < 500)); 
  while(Serial.available() > 0 && i < BufferLength)
    temp =;
    if(temp != 0x0A && temp != 0x22)
      if(temp == 0x0D)
        InBuffer[i++] = ',';
        InBuffer[i++] = temp;
  InBuffer[i] = '\0'; 
  SS1.print("InBuffer: ");
  if(strcmp(InBuffer, ",+CMS ERROR: 321") == 0)
    SS1.println("No Messages");
  else if (strlen(InBuffer) < 40)
    SS1.println("No Messages");
  else if(InBuffer[0]==',' && strlen(InBuffer) > 40)
    Command = strtok(InBuffer, delimiters);   
    PhoneNo = strtok(NULL, delimiters);   
    Date = strtok(NULL, delimiters);
    Time = strtok(NULL, delimiters);
    Sundry = strtok(NULL, delimiters);
    Text = strtok(NULL, delimiters);
    Status = strtok(NULL, delimiters);
    SS1.print("Command/Status: ");
    SS1.print("Phone No.: ");
    SS1.print("Date: ");
    SS1.print("Time: ");
    SS1.print("Sundry: ");
    SS1.print("Text: ");
    SS1.print("Status: ");
    SS1.print("Deleting Message..");
    Serial.print("AT+CMGD=1\r");   //("AT+CMGD=1,4"); // delete all SMS
    if(strlen(Text) < 8) strcpy(PumpCommand, Text);
    strcpy(Sender, PhoneNo);
    while(Serial.available() > 0);     // getting rid of "OK" to deletion   
    return true;
  return false;
7  Using Arduino / General Electronics / Re: N-power Mosfet pc fan control. on: August 05, 2014, 12:51:14 am
I think that diode is meant to be a schottky diode. The schotty and zener symbols are a bit similar. The symbol in the diagram in the OP is not strictly a zenner or schottky symbol but is probably meant to be schottky (without the little 'hooks') as the zenner will let the current past.
8  Using Arduino / Programming Questions / Re: Trying to get single button to start / stop a show - non-blocking on: July 14, 2014, 06:58:25 pm
The point that I was trying to make was not the variable names (even though I "corrected" their spelling in my example) but rather the ShowStarted!==showStated is an evaluation type statement. As such it should have something like "if(ShowStarted!==showStated)...." wrapped around it.

However, I had assumed that you made the mistake of using "=="  instead of "=" for the assertion of the value of one variable to another. Right or wrong, that was the point I was making. 
9  Using Arduino / General Electronics / Re: 4-20ma output from Arduino on: July 13, 2014, 06:18:35 pm
Accidently revisited this thread and saw thats its still alive.

but the author (as always on a forum) never gives the thumps up for what he/she did, that actually works.

I put it in the too hard basket and delayed the project, but I am now looking to revive it.
I have done a lot of Googling since and am leaning towards a simple  op-amp/transistor setup. Like the diagram below, but using an analogue pin and smoothing cap instead of the zenner to provide the input voltage.

I will prototype it in the coming days and  will make up my mind then.
10  Using Arduino / Programming Questions / Re: Trying to get single button to start / stop a show - non-blocking on: July 12, 2014, 07:36:47 pm
ShowStarted !== showStated

Is that meant to read "ShowStarted != ShowStarted" ?
11  Using Arduino / General Electronics / Re: 230V hakko FX-888D? on: July 12, 2014, 07:30:18 pm
..most cannot ship to me, or the shipping costs are stupid.

Buy the iron from the link above ( and it will cost $100 US with shipping to NZ of $42.60 economy or $56.60 expedited. Chuck in the transformer that I listed above (from NZ distributor) at $20. Total cost around $170.
Not bad for a quality iron. Sure its not as cheap as if we lived in US but you know that we have to pay more for living around this side of the world.
12  Using Arduino / General Electronics / Re: 230V hakko FX-888D? on: July 12, 2014, 04:48:06 am
Can anyone recommend where I should buy from.

For the Hako try

For the power coverter try Jaycar

Scroll half way down the page.


It seems very cheap but is made in Australia and therefore has to comply with Aus safety standards (probably similar to NZ).
Says at the bottom of page " Servicing online and through outlets in Australia, New Zealand, USA and Canada."
13  Using Arduino / Networking, Protocols, and Devices / Re: simplemodbusslave with linksprite rs485 converter on: July 05, 2014, 08:55:02 pm
Without  source code and how you've wired up the arduino and converter there is not much that we have to work on to help you.
14  Using Arduino / Project Guidance / Re: Indoor Positioning system using Arduino on: June 28, 2014, 02:11:09 am

As long as the robot is not moving....
True. The faster the robot/person moves the less accurate will be the read position. However far the robot moves in 300ms will be the inaccuracy. Through trial and error the delay period can be decreased thereby increasing the accuracy. Again, without knowing the details of the intended application we cannot know whether this inaccuracy is acceptable.

No. The flash of light would reach the corners in a fraction of a microsecond, unless a corner is over 300m away.

I covered this in Reply #18 when I said "...very minor difference (we are talking about the speed of light over a few metres) in the time...".

At that point there would be a very small known delay for the sensors/brain to process an interrupt and ready for the ping.

Thats what I was referring to when I wrote "..the latency involved in the process of sending and receiving the infrared.." The operative word here being "process".  It covers everything from executing the code to turn on the infrared through propagation of the light waves to the receiver, to processing of the received signal by the micro at the other end.

The ping sent by one source, the corners only need to know the relative time post-known-delay to be able to calculate position.

I'm not clear on what you mean here. Are you changing the paradigm to a scenario where the ping is sent from the robot/person and is received by the corner units?

I'd use relative time because speed of sound changes with temperature and to a lesser extent, humidity.
Fast air flow in the room could fuzz that a bit but fast would be percent relative to speed of sound.

I think over a distance of 10 metres in an indoor environment, this will not be an issue. I made an ultrasonic dam level control (using a Maxbotix sensor) for a farm that this year has had temperatures between 42° C to -9° C  and on occassions, thick fog (i.e. 100 humidity).  The water level range was 8 metres. An external data logger used to verify its operation indicated that it was within 2 cm of true reading despite the wide range of environmental conditions.

I think the OP needs to specify his desired level of accuracy. If he/she wants it down to 0.5mm then he/she can spend a few thousand dollars on an autotracking Total Station. Compact, easy to setup (easier than laying down a wire grid on the floor that would require kilometres or wire for the area in question) and highly accurate but as usual, the cost/benefit trade-off.


15  Using Arduino / Project Guidance / Re: Indoor Positioning system using Arduino on: June 27, 2014, 11:02:03 pm
Since the start the OP has been clear that the room should know where the person carrying the tag is, not the other way around. The robot is a strawman.

When I read the OP, I didn't read it that way but you could be right. If my assumption is wrong then hopefully the OP can clarify the intended use of the system. If so it makes the solution easier still which I will bother going into if the OP gets back to us.
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