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16  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: projector - delay function screws rpm measurem on: February 20, 2008, 05:09:05 am
Thanks Chris,

I've never sampled an internal clock , but I'll look for a reference.

also , I will review some non-arduino code which was already written for this task.

thanks again!

17  Forum 2005-2010 (read only) / Frequently-Asked Questions / projector - delay function screws rpm measurement on: February 19, 2008, 09:44:22 am

I am building a laser projector

and have a problem with the RPM measurement --

I use an interrupt , and the loop() only toggles the laser on and off with delay() functions.

so if I remove the delay() lines the RPM measurement is good , if delay() is used -- not in the interrupt itself but in loop() , the RPM goes crazy and deviates about 20% up/down.

checked for optical interference , none

checked for voltage interference between optical sensor and laser diode with oscilloscope , none

also disabled serial communication , no help

any ideas?

 volatile byte rpmcount;
 float rpm;
 float interval;
 unsigned long timeold;
 volatile unsigned long sig;
 long pausebegin;
 long totalpause;

 void rpm_fun()

 void setup()
   attachInterrupt(0, rpm_fun, FALLING);
   rpmcount = 0;
   rpm = 0;
   timeold = 0;


 void loop()
   if (rpmcount >= 20) {
     //Update RPM every 20 counts, increase this for better RPM resolution,
     //decrease for faster update
       rpm = 60000/(sig-timeold)*rpmcount;
       timeold = millis();
       rpmcount = 0;


//    digitalWrite(13, HIGH);  
//    delayMicroseconds(interval/4);
//    digitalWrite(13, LOW);  
//    delayMicroseconds(interval/4);
//    digitalWrite(13, LOW);  
//    delayMicroseconds(interval/4);
//    digitalWrite(13, LOW);    
//    delayMicroseconds(interval/4);


18  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Battery power for arduino on: July 23, 2006, 06:27:26 am
19  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: arduino RPM meter for laser project on: July 24, 2006, 04:32:27 pm
thanks very much!

20  Forum 2005-2010 (read only) / Frequently-Asked Questions / arduino RPM meter for laser project on: July 14, 2006, 10:37:48 am
I am using arduino to make an RPM meter to read the pulses off an ordinary intel cpu fan with 3 leads (+,-, rpm signal)
I tried using digitalread() and pulsein() but I get fuzzy results.
anyone knows how to read those signals reliably?

code examples:

void loop()
  if (scanvalue!=previous_scan) {pulsecount++; previous_scan=scanvalue;}
   if (millis() - previousMillis > interval)
   interval=((millis() - previousMillis)/pulsecount)*50
   previousMillis = millis();    

   //code blinking code here

21  Forum 2005-2010 (read only) / Frequently-Asked Questions / price est. of arduino BT on: July 23, 2006, 06:29:20 am
heard about the new arduino BT !
anyone has an estimated price??
will I be able to interface it from my BT phone using some applet?
22  Forum 2005-2010 (read only) / Frequently-Asked Questions / arduino laser projector wiring on: July 11, 2006, 09:32:59 am
on my first arduino project i will make a simple pov (laser pov)
the first stage is to get a laser led(s) working from arduino out pins.
so i set up a breadboard with uln2003a darlington chip , and connected the board as shown in this link:

the laser led is working when powered directly from 5v out but not when used through pin 13.
also I should ask for directions about current limiting resistor , though it seems there is one inside already (this is a disassembled laser pointer)

23  Forum 2005-2010 (read only) / Frequently-Asked Questions / more on: May 30, 2006, 08:40:40 am
I made a connection to arduino using examples in 'arduino meets processing' and read a potentiometer.
also I used the 'hello world' program in the Flash site

but to see what arduino is writing I used -- windows hyperterminal..
is there a better way? hyperterm won't let me send , just recieve... and it hangs alot..

is there a demo in processing for sending AND recieving data simultaniously???

thanks Tom
24  Forum 2005-2010 (read only) / Frequently-Asked Questions / working LIVE with arduino - matrix + BIDIRECTIONAL on: May 29, 2006, 11:08:17 am
I understand from these posts that it is pretty easy to control the 8x8 matrix with the maxim chip.
so until the chip arrives from maxim..

I have a question - If I want to send the characters to the matrix LIVE , that means not send code and then disconnect arduino from the computer but have a small applet (visual c? flash?) that I can , for example type a letter into , and that letter would appear on the matrix display.

I understand we are dealing with the serialwrite() serialread().... but how to interface simply?

so - the problem is I know only visual C and basic , so I would need a few example programs if this has to be in other languages.
anyway pointers to example code would be GREATLY appreciated.

also a BIDIRECTIONAL LED MATRIX which can function as an input/output device has been demonstrated in make magazine and hackaday. (link soon) if anyone knows how to implement this in arduino it would be awesome! (even for 2-3 leds)

and keep up the good work
25  Forum 2005-2010 (read only) / Frequently-Asked Questions / lighting bright leds with arduino on: April 26, 2006, 08:49:17 am
i am trying to start my first project with arduino..
I know high intensity leds (around 30ma) need external power.
can I get this power from the arduino power supply?
does anyone have a specific schematic or a ready tutorial for this project?
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