Tag Archive for MCP3008

PiPlanter | Using APScheduler to get timed samples in python

/ 28 April, 2013 / No comments

I’m taking a “break” from my drone while I save some money to buy more tricopter parts, and since the weather’s getting nicer and nicer I’ve decided to start working on my PiPlanter again.

As a refresher, the PiPlanter is a Raspberry Pi powered garden. The goal is for it to just be able to be plugged in and add water to a water source and have the Pi monitor temp and moisture levels to be able to add more water as needed.

I’ve shown that is relatively easy to go from analog sensors to good looking tables and graphs using the raspberry pi, the problem that I ran into however was timing.

It became harder and harder to use the time.sleep function in python to handle long periods of time. When you are dealing with things like plants, you don’t need to water it very often, but for data’s sake, you should be polling the sensors a lot.

I’ve landed on the use of APScheduler in python, and here’s my source code:

 #Timing setup
 from datetime import datetime
 from apscheduler.scheduler import Scheduler
 import time

import logging #if you start getting logging errors, uncomment these two lines
 logging.basicConfig()

#GPIO setup
 import RPi.GPIO as GPIO
 GPIO.setmode(GPIO.BOARD)

GPIO.cleanup()

pin = 26 #pin for the adc
 GPIO.setup(pin, GPIO.OUT)
 led1 = 11 #pin for the short indicator led
 GPIO.setup(led1, GPIO.OUT)
 led2 = 13 #pin for other long indicator led
 GPIO.setup(led2, GPIO.OUT)

#the adc's SPI setup
 import spidev
 spi = spidev.SpiDev()
 spi.open(0, 0)

going = True

#fuction that can read the adc
 def readadc(adcnum):
 # read SPI data from MCP3008 chip, 8 possible adc's (0 thru 7)
 if adcnum > 7 or adcnum < 0:
 return -1
 r = spi.xfer2([1, 8 + adcnum << 4, 0])
 adcout = ((r[1] & 3) << 8) + r[2]
 return adcout

def rapidSample():
 sampleTemp1 = (((readadc(0)*3.3)/1024)/(10.0/1000)) #this translates the analog voltage to temperature in def F
 sampleLght1 = readadc(1)
 samplePot1 = readadc(2)

GPIO.output(led1, True) #turns the led on
 time.sleep(.1) #sleeps a little bit so you can see the LED on
 print "Job 1", datetime.now(),"LDR:",sampleLght1 ,"Pot:",samplePot1,"Temp:",sampleTemp1 #prints the debug info
 time.sleep(.1)
 GPIO.output(led1, False) #turns the led off

def slowSample():
 print "Job 2" , datetime.now()
 GPIO.output(led2, True) #turns the led on
 time.sleep(5)
 GPIO.output(led2, False) #turns the led on

if __name__ == '__main__':
 #the following 3 lines start up the interval job and keep it going
 scheduler = Scheduler(standalone=True)
 scheduler.add_interval_job(rapidSample, seconds=1)
 scheduler.add_interval_job(slowSample, minutes=1)
 scheduler.start()

This produces a loop that flashed a green led on and of for .1 seconds at a time per second, and then every minute, turns on a speaker and a red led for 5 seconds then turns it off. There are some images of what goes on below.

Here is a picture of the the print dialog in python:

You can see that the first job (green led) posts the values from the analog sensors every second

The second job (red led) just posts the time. But the function is expandable to do anything at any time.

Here are pictures of the board and the circuit in action:

Both LED’s off

The Green LED on, the red circled process in the printout

Here are both on

The next step is adding the mySQL in as seen in some other posts.

Category: Cool, Efficiency, PiPlanter, RPi / Tags: , ,

Simple ADC with Raspberry Pi using MCP3008

/ 9 February, 2013 / No comments

Hello!

So for my own benefit, here’s the steps you need to take to get analog inputs working with a Raspberry Pi.

I’m grabbing most of this from: http://scruss.com/blog/2013/02/02/simple-adc-with-the-raspberry-pi/

The first thing you’ll need is an MCP3008. Using jumper wires, hook it up to your pi using this diagram.

Power your RPi up and run the following commands to get it all set up.

First thing’s first, you’ll need to enable SPI in the kernel so:

sudo vi /etc/modprobe.d/raspi-blacklist.conf

Comment out the spi-bcm2708 line so it looks like this:

#blacklist spi-bcm2708

Then run this to make it more permanent.

sudo modprobe spi-bcm2708

Now for the real meat of it. You’ll need these packages for SPI and the WiringPi library makes things a whole lot easier for us.

sudo apt-get install python-imaging python-imaging-tk python-pip python-dev git
sudo pip install spidev
sudo pip install wiringpi

Now everything should be good to go, now for the python.

You can debug this any way you like, but my favorite way to do it is using the program geany. I like to start up a VNC server with root so I don’t get into any trouble with the GPIO permissions.

But here’s the program.


#!/usr/bin/python
# -*- coding: utf-8 -*-

import spidev
import time

spi = spidev.SpiDev()
spi.open(0, 0)
count = 0

def readadc(adcnum):
# read SPI data from MCP3008 chip, 8 possible adc's (0 thru 7)
    if adcnum > 7 or adcnum < 0:
        return -1
    r = spi.xfer2([1, 8 + adcnum << 4, 0])
    adcout = ((r[1] & 3) << 8) + r[2]
    return adcout

while True:
    tmp1 = int(round(readadc(0)/10.24))
    print "in1:",tmp1
    count = count +1
    time.sleep(0.2)

And that’s pretty much it, the result should look something like this:

There you go!

Category: RPi, Uncategorized / Tags: , ,