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1  Using Arduino / General Electronics / Re: Silly mosfet question on: November 15, 2012, 06:08:19 pm
Awesome thanks guys, is this how I would test it if I take it out of the board? Also, I killed the board by accedentally plugging in the keyboard connector wrong and somehow it shorted and refused to turn on again. Any idea on other components I could try?

Thanks!
2  Using Arduino / General Electronics / Silly mosfet question on: November 15, 2012, 04:04:19 pm
Hi,

This might be dumb but I have this old laptop motherboard (not so old, its a core 2 duo) and I see that this mosfet might be dead. Is there any way I can get one of these from a radioshack?

http://pdf1.alldatasheet.com/datasheet-pdf/view/180243/IRF/IRFR3709ZCPBF.html

Also, im not entirely sure it is dead because I tested it by connecting the positive of multimeter to the sink and the negative to the gate. Then I connected neg. to drain and back to sink and the diode test didn't show anything. However, on the other mosfets on the board it gave a reading on the multimeter. Am I doing the test wrong or is the mosfet really dead?

Also, if there is not the specific mosfet in radioshack, can i replace it with a similar one?
 I have this one readily available here and it has the same voltage...can I use this? http://www.alldatasheet.com/datasheet-pdf/pdf/53126/FAIRCHILD/ISL9N7030BLP3.html

Thanks!
3  Using Arduino / Project Guidance / Re: Android controlled RC Car on: August 29, 2012, 07:33:45 pm
What is conventional serial bitstream? I have it doing frequency modulation so the frequency changes from high to low for 1's and 0's but is there a better way to do it? I did consider doing amplitude modulation but there is too much noise. Is there a way to do FFT on an arduino without killing the speed?

4  Using Arduino / Project Guidance / Re: Detecting USB power on: August 29, 2012, 07:26:45 pm
Yes, VCC will be read. VCC is actually analog Vcc. When USB only is plugged in, it is around 5v. When external only is plugged in, it is whatever the supply voltage is against ground pin. This is before the voltage regulator, so it will be whatever you supply it with. This is useful to detect the battery voltage and etc.

@Jackmeph - You should be getting a slight increase in voltage when in USB rather than external supply. For me, it is a really small .12v difference.
5  Using Arduino / Project Guidance / Re: Detecting USB power on: August 29, 2012, 03:22:57 pm
You don't need to connect to analog or digital pin to monitor the voltage:
Try this function and look for spikes:
long readVcc()
{
  long result;
  // Read 1.1V reference against AVcc
  ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
  delay(2); // Wait for Vref to settle
  ADCSRA |= _BV(ADSC); // Convert
  while (bit_is_set(ADCSRA,ADSC));
  result = ADCL;
  result |= ADCH<<8;
  result = 1126400L / result; // Back-calculate AVcc in mV
  return result;
}
6  Using Arduino / Project Guidance / Android controlled RC Car on: August 29, 2012, 03:20:10 pm
Check out my project here:
http://rkrishnan.me/?p=343

My question:
I am having a delay between the computer's signal being sent and the motors kicking in. Any ideas on making things go a little faster between the android and the arduino?

Also, I am having some noise when reading the frequency within the arduino. Any ideas on another method to communicating via 3.5mm jack between arduino and the android phone? I considered FFT, FSK, and ASK. Plz let me know which is best since I dont have much processing power...

Thanks,
Rohit
7  Using Arduino / General Electronics / Re: voltage too low? on: August 22, 2012, 05:05:44 pm
Is there a way then to turn off everything in case voltage goes too low? I can turn off sn754410ne but is there a way to self destruct the arduino? I am now able to get votage reading from arduino.
8  Using Arduino / General Electronics / voltage too low? on: August 21, 2012, 08:29:34 pm
Hi,

I am making an RC car and this is wired as following:

1. I took the cellboost ipr3 apart from the shell and wired everything to this positive and neg.
2. H-Bridge pos/ground connects to cellboost
3. H-bridge (sn754410ne) has 2 powered motors that are pretty small but can draw some current when the car gets stuck
4. Arduino usb 5v connects to cellboost pos.
5. Arduino usb gnd connects to cellboost neg.
6.Arduino usb d+ and d- connects to the cellboost's usb charger d+ and d- pins (which I think are not used by cellboost)

Everything is okay'ish but for some reason, my arduino isn't recognized by computer when I connect the cellboost's usb charge to the computer (even though D+ of arduino is hooked up to D+ of cellboost charging side)

Also, when I run my motor, the motor starts up and the arduino just resets for some reason. I suspect this is a current draw problem since both problems get sorted out when I hook up the arduino/h-bridge with seperate power (instead of cellboost power).

My question is: do you think an arduino and 2 motors can be hooked up directly to the lipo (rather than via the cellboost's charging circuit) or is there a reason for having a current limiting thing in the cellboost's circuit? It was initially designed to run an ipod shuffle so I think my new circuit takes in a lot more current than an ipod does. This would mean the internal safety current limiter thing would be useless for me. However, would the lipo explode if I connect the motor to it? I am worried the 2 of them would take too much current. Here is a pic of a similar sized motor in an rc car just to get an idea:
http://www.world-trades.com/photo/929/9301/rc-car-193.jpg

Thanks!
9  Using Arduino / Microcontrollers / Re: Not working without isp on: August 14, 2012, 08:44:35 am
my sketchLconst int analogOutPin = 0; // Analog output pin that the LED is attached to


void setup()
{
  pinMode(analogOutPin, OUTPUT);  

}
// the loop routine runs over and over again forever:
void loop()
{    
         digitalWrite(analogOutPin, HIGH);
delay(1000);
             digitalWrite(analogOutPin, LOW);
             delay(1000);
}


I managed to find out that the microcontroller stops working whenever I disconnect VTG or MOSI from the ISP. Im not sure why but these two pins always need to be connected for the chip to start working. Any ideas? could it be a crystal problem?
10  Using Arduino / Microcontrollers / Re: Not working without isp on: August 13, 2012, 05:38:54 pm
I am using a benchtop power supply and giving 3.8v to pin 8 and pin 4 of the attiny13 microcontroller (Vcc and GND)

MOSI, MISO, and SCK connect directly to my ICSP header pins

My circuit has a 4.7Ohm resistor between VCC and Reset (pin 8 and 1 of the attiny13)

For some reason, if I probe reset and ground when programmer is connected, I am getting a constantly fluctuation voltage from 0v to 2.5v and back and forth.

Also, it seems to work for a second when I bridge Reset and ground. As soon as I disconnect the bridge, it works for a second and stops functioning. When I bridge it again and let go, it works again for a second until it stops again.

Thanks,
Rohit

11  Using Arduino / Microcontrollers / Re: Not working without isp on: August 13, 2012, 05:26:56 pm
my existing circuit has a 4.7K resistor between reset and Vcc and it still only works when I connect the 6-pin isp header. I measure the voltage across Gnd and Reset and i'm getting approx 3.8v. Is this okay? What is the programmer doing that I can emulate when I disconnect?
12  Using Arduino / Microcontrollers / Not working without isp on: August 13, 2012, 05:08:23 pm
Hi,

I have a simple circuit with a potentiometer that my attiny reads and varies the duty cycle of a HIGH and LOW signal. For some reason, this thing is only working when my avrispmk2 is plugged in. The minute I disconnect, the thing doesn't work. I suspect it has something to do with reset pin but Im not sure whether to make it always grounded or always high. Plz help

Thanks!
13  Using Arduino / Displays / Re: Varying opacity of LCD on: July 02, 2012, 08:16:53 am
Thats exactly what I thought and tried, but the black is only stopping visible light for some reason. Also, when I do black and look at it under a microscope, it is just individual red, green, and blues. Is there any way to make every pixel actually black?
14  Using Arduino / Displays / Varying opacity of LCD on: July 02, 2012, 08:11:28 am
Hi,

I am trying to do this project with an lcd and the intention is to be able to pass ultraviolet light through certain parts of the LCD. I need to be able to turn certain pixels "opaque" to UV and other pixels allow UV to pass. Is there any way to do this via software? It doesn't necessarily have to be arduino but I want to be able to control where UV gets reflected and where it passes through it.

By the way, I am referring to just the LCD without the backlight, bezel, or polarization filters.

I have a standard tft laptop lcd.

Thanks,
Rohit
15  Using Arduino / General Electronics / Re: Question on constant current on: June 25, 2012, 09:20:04 pm
Hmm...I see your point, but is there anyway then that I can run a couple of dc motors for an rc car off a cordless phone NiMh battery then? I have the charger all set...
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