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Topic: Accelerometer and Transistor (Read 487 times) previous topic - next topic

redcomet782

Dec 06, 2012, 09:19 am Last Edit: Dec 06, 2012, 09:21 am by Coding Badly Reason: 1
Here is my program, I want to

1) The microcontroller, Arduino UNO R3 sends 3.3V to the sensor, Accelerometer, MMA7361

2) The sensor turns on and send signal to the microcontroller.

3) When I move the sensor and if the voltage becomes more than 2V, the microcontroller sends 1.5V to the Transistor. Otherwise send 0V.

Code: [Select]
int outputPin1 = 3;   // Pin D3
int outputPin2 = 5;  // Pin D5
int analogPin = 0;  // Input Pin A0

void setup()
{
 pinMode (outputPin1, OUTPUT);
 pinMode (outputPin2, OUTPUT);
 Serial.begin(9600);
}

void loop()
{
   int volts = 170; // send signals of 3.3v
   analogWrite(outputPin1, volts);  // to Accelerometer

   int reading = analogRead(analogPin);  //  receive signal
   delay(1000);    // delay 5sec.
   
   if (volts >= 100)    // Input voltage is more than 2.0V
   {
   int volts = 77; // send signals of 1.5V
   analogWrite(outputPin2, volts);  // to Transistor
   }
   else
     {
     int volts = 0;
     analogWrite(outputPin2, volts);  // to Transistor
     }
}


When I measure with DM meter, it's keep showing 1.5V even it doesn't change the position of the sensor.
I guess there's some problem in the if, else.


Moderator edit: [code] [/code] tags added.

AWOL

Code: [Select]
int volts = 170; // send signals of 3.3v
    analogWrite(outputPin1, volts); 

Is turning an accelerometer on and off at 490Hz a good idea?
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Grumpy_Mike


Code: [Select]
int volts = 170; // send signals of 3.3v
    analogWrite(outputPin1, volts); 

Is turning an accelerometer on and off at 490Hz a good idea?

Especially as you will be feeding 5V into a 3V3 device. You might have just fried it.
Dispute the name analogWrite noes not produce an analogue voltage.

redcomet782

#3
Dec 07, 2012, 12:25 pm Last Edit: Dec 07, 2012, 12:31 pm by redcomet782 Reason: 1
I just revised my code like this:
-----------------------------------
Code: [Select]

int outputPin1 = 3; // Pin D3
int outputPin2 = 5; // Pin D5
int analogPin = 0; // Input Pin A0

void setup()
{
   pinMode (outputPin1, OUTPUT);
   pinMode (outputPin2, OUTPUT);
   analogWrite(outputPin1, 170);  // send signals of 3.3v to Accelerometer
}

void loop()    
{
   delay(1000);    // delay 1sec.

   if (analogRead(analogPin) >= 100)    // Input voltage is more than 2.0V
   {
       analogWrite(outputPin2, 77);  // send signals of 1.5V to Transistor
   }
   else
   {
       analogWrite(outputPin2, 0);  // 0v to Transistor
   }
}


-----------------------------------------

It looks like Accelerometer is working properly which sends different voltage when I change the position, BUT when I measured the voltage of outputPin2, Pin D5, it's keep showing 1.5V even I change the direction of the sensor that has to show 0V.

Does it mean the microcontroller doesn't receive the signal from the accelerometer properly or some part is missing in the code?

AWOL

#4
Dec 07, 2012, 12:27 pm Last Edit: Dec 07, 2012, 12:45 pm by AWOL Reason: 1
Quote
analogWrite(outputPin1, 170);  // send signals of 3.3v to Accelerometer

Does it, really?
Or does it just send a 66% duty-cycle 5V, 490Hz signal?

If you want to power a 3.3V device, it is much simpler to use the 3.3V output provided on the board.

Please use [font=Verdana][[/font]code][font=Verdana] [[/font]/code] tags when posting code.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Grumpy_Mike

Your meters are not reading the right value because you are trying to measure rapidly changing voltages, meters don't read those correctly.

You can not use the analogue write to set a voltage on the pin, it just produces a 5V square wave.
I did say this before but I think you did not understand. DO NOT DO THIS.

dc42

#6
Dec 07, 2012, 09:04 pm Last Edit: Dec 07, 2012, 09:06 pm by dc42 Reason: 1
Not only can you not send 3.3V to the accelerometer using analogWrite, you can't send 1.5V to the transistor either.

To power the accelerometer, just use the 3.3V supply pin on the Arduino - as has already been said.

As for the transistor, is it a bipolar transistor, a darlington transistor, or a mosfet? The first 2 of these are current-operated devices, so you should drive them direct from a 5V digital output pin via a series resistor. A mosfet is a voltage-operated device, but most discrete mosfets need more than 1.5V anyway. if you tell us the part number of the transistor and what device it is driving, we can offer advice.

Also, you are comparing the result of analogRead with 100, but the comment says you are testing for more than 2V. 2V on the pin will give you a reading of (2/5 * 1024) = 409.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

redcomet782

i'm sorry that I didn't notice that there has a 3.3V output on the board.

When I use the 3.3V pin, instead of outPutPin1, Pin D3, how I should edit the code?:

Code: [Select]
analogWrite(outputPin1, 170);  // send signals of 3.3v to Accelerometer



And the transistor I'm using is the NPN transistor.

-----------------------
General-purpose silicon, high-speed, medium control switching transistors. Rated 600mW. Case Type TO-92. Includes 5 of 2N2222, 5 of 2N4401 and 5 of 2N3904.
-----------------------
General Features
Model      276-1617   
Product Type      Transistors   
Enclosure Color      Black   
Body Material      Multi

AWOL

Quote
When I use the 3.3V pin, instead of outPutPin1, Pin D3, how I should edit the code?:

The 3.3V is always there, irrespective of the code you run.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

redcomet782

Thanks, I got it.

And what's the good way to send the output signal, instead of using

Code: [Select]

analogWrite(outputPin2, 77);  // send signals of 1.5V to Transistor

Grumpy_Mike

Just set the digital output pin high. The resistor you put between the output pin and the transistor's base will keep the current down and switch the transistor on. There is no need to supply a specific voltage to the transistor.

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