Arduino - Acceleration Due to Gravity Testing Rig

I made the rig in the picture to measure acceleration due to gravity, just for fun.

The hardware is just a home made electromagnet powered through a ULN2003 (linking  2 channels to boost current). This was controlled using an Arduino Nano. I added an LED to indicate when the electromagnet was activated, and a button to activate it. The switch that detected the ball hitting the ground was also home made from a peg, some paperclips and tin foil:

The plan for the program was:

• Push a button on the rig to activate the electromagnet for long enough to attach a bearing but not so long it burns out the hardware (4 seconds seemed about right)
• Switch off the electromagnet automatically and simultaneously start a timer.
• When the pressure switch is activated by the ball hitting the ground, stop the timer.
• Work out the acceleration using a = 2s / t**2 
• (s= distance fallen, t is the time)

I started the code in Ardublock because it avoids typing errors, but the calculations refused to give a valid result even when the timing was giving valid readings. After a frustrating hour of trying to fix it within Ardublock, 3 minutes with the actual code in the Arduino IDE had it working well. The erroneous values are when the ball missed the switch and I had to trigger it manually.

 The code:

https://github.com/jcwyatt/gravityfalls

AM2302 Temperature and Humidity Sensor - Bat Project #01 - Durrell, Jersey

In this post I'll detail how I fared with getting a AM2302 working with the RPi.

This is the first step in a project I'm working on for Durrell Wildlife Conservation Trust. As well as working on a Gorilla feeder with my friend Max, they were also interested in data logging for their bat house:




I bought a sensor from eBay for a few pounds.

From what I can understand, the output from these devices is a digital stream of bits containing the relevant data, but it is not in a regular format like I2C, therefore you have to download a special library. I followed the instructions from Adafruit and it worked really well.

I wasn't that bothered about uploading my data to a google sheet, but since I discovered Thingspeak
a few days ago, I've been itching to try it. It's a great solution for the zoo project because the data goes straight to the web and is formatted and graphed automatically, and can be made public.

I found a great tutorial for linking python to thingspeak here:

http://www.australianrobotics.com.au/news/how-to-talk-to-thingspeak-with-python-a-memory-cpu-monitor

I just adapted the code and added it to the Adafruit example code. Resulting code is messy but worked really well.

I developed this using a model B+ but once it was running I shrunk it down onto a headless Pi Zero.

The thingspeak project site for the trial data (from my lounge) is here:

https://thingspeak.com/channels/103719

And you can embed the graphs using an iframe embed code. I presume this will update as data gets added, but I don't yet know for sure.




Hardware wise I set it up exactly as shown in the diagrams of the tutorial, but added a blue LED between the data and ground pins of the AM2302. It was a lucky guess and works nicely, flashing brightly as data is sent to the pi every minute.

(Sidenote: I've been trying out Node Red recently and I love it, but the instructions I could find online for getting the sensor to work in Node Red seem out of date and I ran into errors trying to install the nodes.)


The code:

#!/usr/bin/python
# Copyright (c) 2014 Adafruit Industries
# Author: Tony DiCola

# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
import sys
import httplib, urllib
import Adafruit_DHT
from time import sleep

# Parse command line parameters.
sensor_args = { '11': Adafruit_DHT.DHT11,
    '22': Adafruit_DHT.DHT22,
    '2302': Adafruit_DHT.AM2302 }
if len(sys.argv) == 3 and sys.argv[1] in sensor_args:
 sensor = sensor_args[sys.argv[1]]
 pin = sys.argv[2]
else:
 print 'usage: sudo ./Adafruit_DHT.py [11|22|2302] GPIOpin#'
 print 'example: sudo ./Adafruit_DHT.py 2302 4 - Read from an AM2302 connected to GPIO #4'
 sys.exit(1)

# Try to grab a sensor reading.  Use the read_retry method which will retry up
# to 15 times to get a sensor reading (waiting 2 seconds between each retry).

while True:
 humidity, temperature = Adafruit_DHT.read_retry(sensor, pin)

# Un-comment the line below to convert the temperature to Fahrenheit.
# temperature = temperature * 9/5.0 + 32

# Note that sometimes you won't get a reading and
# the results will be null (because Linux can't
# guarantee the timing of calls to read the sensor).  
# If this happens try again!
#Pushing data to Thingspeak
# python

        if humidity is not None and temperature is not None:
                print 'Temp={0:0.1f}*  Humidity={1:0.1f}%'.format(temperature, humidity)
        else:
                print 'Failed to get reading. Try again!'
                sys.exit(1)


 params = urllib.urlencode({'field1': temperature, 'field2': humidity,'key':'92P5L3PGPTT8ZE8N'})
 headers = {"Content-type": "application/x-www-form-urlencoded","Accept":"text/plain"}
 conn = httplib.HTTPConnection("api.thingspeak.com:80")
 conn.request("POST", "/update", params, headers)
 response = conn.getresponse()
 print response.status, response.reason
 data = response.read()
 conn.close()


 if humidity is not None and temperature is not None:
  print 'Temp={0:0.1f}*  Humidity={1:0.1f}%'.format(temperature, humidity)
 else:
  print 'Failed to get reading. Try again!'
  sys.exit(1)
 
 sleep(60)

Node Red

I've had a play with Node Red for the first time tonight. In a matter of minutes I was able to operate an LED through the Node Red interface, something I'd been wanting to do for a long time.

I couldn't be much simpler to use. I could do quite a lot of things in Node Red after just one evening playing around. The web side of things is still puzzling for now, with websockets and HTTP the next nut to crack.

I reckon I could control my home heating now just using Node Red and the right hardware.

LATER THAT SAME EVENING........

Couldn't let it lie so I had another play. Now the status of the LED can be output to wherever, e.g. twitter:

Output:

Copy and paste the code below if you want to try it (minus the twitter feed) - I used pin 11 (GPIO 17) to drive the LED.

[{"id":"d82e83d.f27d18","type":"inject","z":"2fc3a5ef.d03c5a","name":"LED on","topic":"","payload":"1","payloadType":"string","repeat":"","crontab":"","once":false,"x":295,"y":112,"wires":[["24897f1c.db768","1b8bd14c.e4742f"]]},{"id":"795f97e3.86a068","type":"inject","z":"2fc3a5ef.d03c5a","name":"LED off","topic":"","payload":"0","payloadType":"string","repeat":"","crontab":"","once":false,"x":297,"y":187,"wires":[["24897f1c.db768","1b8bd14c.e4742f"]]},{"id":"24897f1c.db768","type":"rpi-gpio out","z":"2fc3a5ef.d03c5a","name":"Yellow LED","pin":"11","set":true,"level":"0","out":"out","x":497,"y":146,"wires":[]},{"id":"4a42382a.b5bdc8","type":"debug","z":"2fc3a5ef.d03c5a","name":"LED status","active":true,"console":"false","complete":"payload","x":622,"y":286,"wires":[]},{"id":"1b8bd14c.e4742f","type":"change","z":"2fc3a5ef.d03c5a","name":"Create Human Readable Output","rules":[{"t":"change","p":"payload","from":"0","to":"LED is OFF","re":false},{"t":"change","p":"payload","from":"1","to":"LED is ON","re":false}],"action":"","property":"","from":"","to":"","reg":false,"x":356,"y":287,"wires":[["4a42382a.b5bdc8"]]}]

Hacking a ridiculously cheap laser.

I bought a couple of really cheap lasers off of eBay for a project I wanted to try at codeclub (Mission impossible style burglar detector using LDRs and lasers). They were about £1.50 each from China. Like this one but cheaper.

They were not easy to use in the chassis they came in, having a momentary push button switch, and eating batteries, so I set about taking one apart.

The chassis needed a bit of hacksaw work to split, and then the controlling chip and laser came out as one. I jammed on the switch with a cable tie, and taped the +ve wire to the body with insulating tape. The spring on the chip is the -ve:

Not quite sure of the power requirements but I think I would power it through a ULN2003 and an external battery supply if I was to include it in a project. Claims to be 1mW with 3V input. My multimeter read 25mA being supplied from the arduino 3.3V pin.

Not sure what project to include it in.

Robot Chassis - PoliceBot project

My son and I spent a bit of time this evening trying to get a robot chassis working.

My daughter and I built it a week or so ago:

This evening my son and I had a go at programming it to do something:

We used my new favourite programming tool - ardublock:

My son found some blue and white LEDs in my kit box, so we decided to make it into a police car.

It was really easy to get going.

I had a few problems with dodgy connections so we ended up soldering the power connections from the battery to the motors.

The next step is to activate the ultrasonic sensor on the front of the chassis.

Dodgy HC-SR04 Ultrasonic Distance Sensors

I've had a few issues trying get ultrasonic sensors working recently.

I'd had no problems previously when I'd used Flowol software to get one working with the boat project, so initially I suspected it was me trying to use Ardublock that was the problem, or just lack of skilled wiring on my part.

Turns out it was 4 dodgy HC-SR04 I'd bought through Amazon from China.

I built the circuit and tried the Newping sample sketch on one of the Amazon HC-SR04s. No reading on the serial monitor when using the Newping (well actually a continous zero reading)

I tried each of the sensors in turn, and as soon as I put an older SR04 I had lying around in the circuit, I immediately got good numbers in.

God to isolate the problem, but sucks to have to either return the parts or write them off and buy more.

At least knowing I had a good sensors let me try out the Ardublock program again, this time with some success, although it wouldn't read above 20cm.

Arduino with Bluetooth and ArduBlock

My daughter has a holiday project to build a robot, so we are adding Arduino controlled features.

I've tried to get bluetooth working with the arduino before with the boat project. But failed for whatever reason.

I recently discovered Ardublock, which is great way to get a program working without getting bogged down in the typing. It tops S4A because you can upload to the Arduino, and see the actual code it is creating:

This worked well and had the pin 13 LED blinking.

I attached the HC-06 bluetooth chip to the arduino and loaded up the Bluetooth Serial Controller App.

Once the HC-06 was paired (easy to do if you're used to pairing speakers and stuff regularly) the app was able to send '5' to the Arduino and get the LED blinking.

Now do do a few more adventurous things with the robot.