I just signed-up to the forums, and I've been playing around with the Arduino.
So I've got a project
So I'm trying to make a Barometric Pressure Sensor with using only 2 digital and 1 analog pins on the Arduino AtMega 328. But the Pressure Sensor that I'm using is the MPL115A1T1CT-ND and it already has a built-in ADC and SPI. It needs a minimum of 5 pins (digital) from the Arduino. I can only use 3 at the most. Here's the link of the pressure sensor that I am trying to interface with the Arduino:
Please Help, I'm not really sure how I'm going to work this out. I was thinking Multiplexer but the kit sensor is SPI or something, which I have no clue how SPI is relevant...
If you have buy a sensor, take a look at the websites of Sparkfun and Adafruit.
They provide everything you need: datasheets, examples, links, a forum, etc.
Now you have a sensor, with little information, and not often used with the Arduino.
Which Arduino board do you have? I hope it is the Arduino "Uno", that is the most common board.
First off: My Arduino is the Arduino Aceduino AT Mega 328 with 15 digital pins and 5 analog pins.
Second: What's the difference between the I2C and SPI? You say the I2C needs only two pins? How did you immediately know?
But this is great for me...
And thirdly I'm just trying to print the barometric pressure on the Serial Monitor.
The only challenge is that I can only use 3 of the 15 digital pins. The Voltage source and the ground are not counted... Therefore I just have to reduce the 6 pin of the sensor to 3 pins... Any more ideas?
I read the freescale page better this time.
Sensor MPL115A1 is SPI
Sensor MPL115A2 is I2C
So I was wrong, sorry. Your MPL115A1 has only SPI.
According to the datasheet: There are 8 pins on the sensor.
VDD : 3.3V or 5V
GND : ground
CAP : 1 uF
/SHDN : connect to VDD for normal operation
SCLK, DOUT, DIN, /CS : this is the SPI interface.
So you need 4 pins for the SPI interface.
Can you use an analog pin (they can be used as a digital pin).
You could perhaps use an 74HC595 shift register for extra outputs. I don't know what the others pins are used for, but for relays or leds, the 74HC595 provided 8 extra outputs, and it needs 3 Arduino pins. More 74HC595 can be linked together to get 16, 24, 32 and more outputs. And still only those 3 Arduino pins are used.
(Same exact color too) Also I could use analog pins but they count. So example, I could use 1 analog pin but only 2 digital pins..
Now we're passed that, I will follow your suggestion on the shift register. If I got this correctly, I connect the 4 SPI pins of the sensor to the Shift register which in turn connects to 3 output pins to the Arduino? If that's right, then all I have to worry about is the programming...
No, for the SPI it is much easier if they are connected directly to the Arduino. And one of the signals is a input.
That's why I mentioned leds and relays.
Wat are the other pins used for ?
Are you sure you want to continue with this ?
If you can arrange an extra spare pin somehow, you still have to write the program.
The BMP085 is a more common used baromic sensor for the Arduino:
Sadly, I've been looking for a BMP085 here in my country, but they're not available.
If I can't get a work-around on the 3 pins, then I guess I'll have to use 4 pins. The rest of the pins will be used for other detectors such as humidity sensor, temperature, etc. I'm trying to make a mini weather station with only one Arduino board...
The three pin limit by the way is just to see if I can reduce each sensor's pins... It's just that this Pressure sensor is giving me trouble because it's SPI...
I'm pretty sure that you should be able to make one more pin available.
Perhaps you can share a few pins ?
Is there perhaps an other sensor with a chip select ?
If the MPL115A1 is not selected (/CS high), the other pins (DOUT, DIN, SCLK) may be used for something else.
I don't know if you are willing to upload the schematic with all sensors, that would make it easier to help you.