Thursday, December 14, 2017

What is my Ultimate Raspberry Pi Station?

As I'm working on several Raspberry Pi hosted web/database/IOT projects this Christmas Season, I wanted to share my ultimate workstation.

First of all you need a Raspberry Pi. Now that version 3 is out, I got rid of all my older units and replaced them with this little wonder computer. The integrated WiFi and Bluetooth, plus the faster speed makes a useful computer into a absolute necessity!

I start with this Raspberry Pi Starter Kit which includes the Raspberry Pi 3, a 32gb SD Card, Power supply, and a HDMI cable.



Now, the case that comes in the kit is a fine case, but I wanted to mount mine on the back of my TV to keep it and the wiring out of the way. This VESA case can also mount on a wall or under a shelf.



Again, with the minimal wiring goal, I use a Logitech wireless keyboard / mouse combo.



And did I mention I use a TV? Yes! A inexpensive HD LCD with a HDMI input for the Pi, and I can still catch a game or movie when I need a break from programming!


Last, but not least, you may need a VESA hardware kit to fit your tv. This kit covers most TV models and will make it easy to mount your Pi on the rear of the TV.


So that's my setup, What is your preferred setup?






Tuesday, November 21, 2017

Arduino and Raspberry Pi Holder

When you are building circuits and programming your microcontroller, you probably have it sitting on a table, wires going everywhere, and possibly shorting the bottom pins on clipped wire pieces, tools, and other obstructions. It can be a challenge to keep everything tidy and organized, which can cause trouble shooting issues. I'm looking forward to my new organizer coming this week, and I will post video of it in use. It allows me to keep a Raspberry Pi, Arduino, and a breadboard stable and secure. Projects have a higher possibility of working the first time, as I can see better if wires are going where they are supposed to, and have not pulled loose!

Arduino / Pi / Breadboard Base

Wednesday, November 15, 2017

Model Railroad DCC Control - JMRI / Raspberry PI

For those who want to control their DCC Model Railroad with their cell phones or tablets (pretty much any Android (Engine Driver) or IOS (WiThrottle) device), There is a Raspberry Pi image already built. Copy it to a sdcard, insert into your Raspberry Pi, and you are pretty much set to go!

Once you've assembled the hardware and installed the image, connect your RPi to your layout via PR3, LocoBuffer-USB, NCE Serial, NCE USB, SPROG or DCC++, and plug in the RPi's power adapter.  You should see some LEDs on the RPi begin to blink, and shortly, using your wifi-capable phone, you'll see a WiFi network named "RPi-JMRI".  Select it and enter "rpI-jmri" when prompted for the key (note that 3rd character is a capital "eye").  Open EngineDriver on your phone, and you should have an available connection under Discovered Servers called "RPi-JMRI".  (Similar with WiThrottle on iPhone).  Enter loco address and run trains!

Tuesday, November 14, 2017

Breadboard Friendly ESP8266-01 / nRF24L01+

The cheapest WiFi modules on the market (around $3 each) are the ESP8266-01 boards, which are WiFi enabled microcontrollers in their own right (with limited I/O), or they can be used with an Arduino as the WiFi interface. However, they have a funky 2x4 header that is not breadboard friendly.

Here is one possible solution. A inexpensive 2x4 to breadboard converter with a 2x4 socket on top and headers on bottom that match up nicely with a breadboard. It not only works with the ESP8266-01, but also works with the nRF24L01+ RF modules as well.

Now it's very easy to experiment with these handy modules. If you need a 5v to 3.3v regulator and level shifting for your ESP8266-01, check out these converters!

More ESP8266 Fun!

We have shown how to use the ESP8266 to collect sensor data, and send it to a database (client mode), but you can also use the ESP8266 as a webserver, displaying a web page and showing status or accepting input (server mode). In fact, it can be a server and a client at the same time. The following code runs a webserver on the esp8266, providing input fields to instruct the esp8266 to perform an action, and then POSTs that set of actions to the database. You could also read a sensor to verify that the actions were actually performed.

Code



 

Tuesday, September 26, 2017

Calculate Daylight Savings Time Date

The web based apps I write often have informative messages for the users, and one request was a reminder to change the clocks for Daylight Savings Time. Since it's not the same date each year, but is always the Second Sunday of March and the First Sunday of November, I needed to be able to get a date for those days. It's fairly easy in PHP, as you can see below.



$year = date('Y');
$spring = date('m-d-Y 02:00:00 A', 
strtotime('Second Sunday Of March '.$year)); $fall = date('m-d-Y 02:00:00 A',
strtotime('First Sunday Of November '.$year)); echo 'Spring: ' . $spring; echo 'Fall: ' . $fall;
Here is the quiz of the day:

How would you accomplish this on the Arduino?

Reference:

Arduino Time Libraries

Arduino DST Solution

Friday, August 25, 2017

Arduino / Relay Interference

Symptom: 

You have a relay connected to your Arduino, and after a while your Arduino stops running. That's not supposed to happen, these things loop forever, right?

It's a common issue when running inductive loads from a Arduino controlled relay. Many folks think it's a voltage problem and try throwing capacitors on the relay supply, or using a opto isolated relay (separate power and ground). These solutions may work, but more often than not, they don't.

Cause: 

So what is causing the problem? It's EMI!
The back EMF from an inductive load causes the relay contacts to act like a spark gap transmitter, scrambling the processor. The Atmel chips are very susceptible to RF.

Not to worry, it's not permanent, it clears when you cycle power.

How did we discover this and how do you keep it from happening?

We have a project where a Nano and a common relay board are installed in a small case. When all the parts are assembled on the bench, it works fine. When crammed together in the box, it works for a while, then freezes. But only with a inductive load attached to the relay. With no load, or a resistive load, it runs forever (well, 3 days or more, forever was too long a test period). We have tested this six ways to sunday with a variety of Arduino and Arduino clones.

Solution:

Installing snubbing diodes on relay coils and motors (the common solution) can be difficult (they don't work on ac devices) or void a warranty on many household appliances.

I series connected a resistor and a capacitor together, and connected those across the Arduino relay contacts (as close to the relay contacts as you can get). This quenches the back EMF, and prevents the Arduino from locking up. There you go, a $0.30 solution to a nagging problem.

Make sure your capacitor is rated for the voltage you expect to see. I used a .1 uF 50v Tantalum, and a 100 Ohm 1/4w resistor on a 26v circuit. My load was another relay. In another application, the load was a 120v motor, so the cap was 150v.


Tuesday, August 22, 2017

2 Channel IR Interface

Recently we produced a 6 Channel IR interface for IR transceivers like the TCRT5000 pairs. Lots of Model Railroading and other object detection applications. Now we have the less expensive 2 channel version available. Same code, same components, just less of them! - $30 + S&H


Harbor Freight Caliper Interface

Did you know the inexpensive Pittsburgh / Chicago Tool / Harbor Freight Calipers (4 pin dataport under battery cover) have a digital interface? We can read that interface with an Arduino, just like we do with the Mitutoyo / Igaging calipers and micrometers. The electrical interface is different, as is the data stream. Now, thanks to the hard work and experimentation of the folks at Arduinotronics, you can integrate measurement into your projects. I'll be posting video, code and schematic shortly, but get your board order in now so you can get started! $15 + S&H






Friday, August 11, 2017

Setting up a Mosquitto MQTT IOT Broker

Ever want to view / control devices at home while on the road?

As part of our IoT initiative, I have set up a broker based on Mosquitto. Mosquitto uses MQTT, a publish and subscribe mechanism that avoids the necessity of special router configuration on your home network. A sensor node (arduino with ethernet or wifi, esp8266, etc.) publishes data to the public broker, and a client (cell phone, another arduino, etc.) subscribes to that topic to display information or receive instructions. Since the device that subscribes, or publishes to the broker initiates the conversation, your home router does not need network address translation or ports opened up. To secure the data transmission, usernames, passwords, client id's and SSL are used.

Our first step was to install Mosquitto on the server. We used the excellent tutorial at https://www.baldengineer.com/mqtt-tutorial.html to get the broker up and running, and tested. Since we used a windows 10 machine as the server, we had to enclose the message "Hello World" in double quotes instead of single quotes as stated in the tutorial.

There are two dependencies listed during the installation, so also download those, and copy the resulting dll's to the mosquitto directory.

Since I use MySQL and PHP to collect data from our sensors and log to the database, I created a php page that acts as a publisher to the broker. The sensor could just as easily publish to the broker directly, but I needed the database and visual graphing capability of PHP, CSS3, HTML5 and Javascript. I can also easily email alerts.

I may set up php as a subscriber, and have the sensors publish to the broker.

To use MQTT with PHP you need a MQTT Library for PHP.

Stay tuned for more articles using ESP8266's, relays and other sensors, with MQTT transport. I'll have a Mosquitto sandbox for readers to play with so you can publish and subscribe your sensors.

PHP Example Code:

https://pastebin.com/X2iewi60

Android viewing and control:

There is an very good Android dashboard for publishing and subscribing to the broker. You can see your sensor values, and send commands to your devices from anywhere in the world.

IoT MQTT Dashboard

Thursday, July 20, 2017

Infra Red Sensor Boards are Here!

The IR Sensor boards finally arrived! We are busy soldering components, writing new Arduino sketches to show off the capabilities of these boards, and preparing for full blown production. New videos are in the works, for when we get back from vacation. Each board supports up to 6 sensors (Reflex or Transmissive), and are ideal for block detection, crossing light / gate sensors, scale speedometers, and more.

The main difference between reflex couplers and transmissive sensors is in the relative position of the transmitter and detector with respect to each other. In the case of the transmissive sensor, the receiver is opposite the transmitter in the same optical axis, giving a direct light coupling between the two. In the case of the reflex sensor, the detector is positioned next to the transmitter, avoiding a direct light coupling.

Using a 6' piece of cat-5 cable, we connected the blue to the Anode of the IR LED, and blue/white to the Cathode. We connected green to the Collector of the photo transistor, and green/white to the Emitter.

I suggest a bit of hot glue once you solder and heat shrink the leads to the TCRT5000 IR pair.

On the board end, blue goes to LED+, green to PT+, and the blue/white and green/white to GND.

See our level crossing application, and our scale speedometer project.






Sunday, July 2, 2017

Posting ESP8266 weather data to server

Last week we connected a ICStation BME280 temperature / humidity / barometric pressure sensor to a a ICStation NodeMCU ESP8266. We displayed the collected data (along with Dew Point and Heat Index calculations) in the serial monitor.

This week we modified the sketch to post those variables to a linux server (could be your own local Raspberry Pi) running MySQL and PHP. We have it set to take a reading every 30 seconds, and post the data to a php page that inserts the data into the MySQL database. The index page displays a table of that data. The time and date stamp has been modified to display the data in the timezone of the location of the sensor. We are working on live gauges and graphs to display this data in real time.''

See the live data at http://theiot.zone/templog/

All code can be downloaded from https://drive.google.com/open?id=0ByRIq5k2wjcSXzVvamZ1dk9yQVU

Thanks to Nuno Santos and his tutorial at https://techtutorialsx.com/2016/07/21/esp8266-post-requests/ for some fine tuning of my code.


Friday, June 30, 2017

Median vs. Average, Arduino Calculations

If we want to average a set of numbers, we add them together, then divide by the number in the set.

150 + 200 + 0 = 350 / 3 = 116 Average

I'm using int and dropping the fractional parts. Use float if you need them.

But if we want the Median, which is the center, or middle number, we have to sort and compare each number to the others to get a list from high to low, and grab the center number. In this case, the Median is 150.

I've written a sketch that calculates both so you can compare your own numbers, and make it a much larger list:

int a[] = {150,200,0};
int n = 3;

a[] is your set of values

n is the number of values in the set

https://pastebin.com/Ge0pZGS2

More info on Mean, Median & Average - https://www.vocabulary.com/articles/chooseyourwords/mean-median-average/





Thursday, June 29, 2017

6 Channel Infra Red Transceiver Sensor Board

Calling all Model Railroaders (ok, it's not just for Model Railroading)! Remember our Scale Speedometer and Crossing Light project? We used IR transceivers in the track to detect a train passing overhead. Perfect for block detection and other projects. We are releasing a 6 channel IR sensor board (fully populated) for use with Arduino, Raspberry Pi, PIC and other microcontrollers. Comes with all components, including the 6 IR transceivers wired to 6' cords. All connections are screw terminals for ease of use. Each phototransistor has a potentiometer for adjusting sensitivity. Operates at 5v or 3.3v (select which version). Comes with sample code for Arduino.

Voltage Options

Sunday, June 25, 2017

Transistor Sizing Calculation

Two common ways of using a transistor is as an analog amplifier, or a digital switch. We are most interested in the digital switch mode of a transistor in our projects.

Many times, an Arduino, or other microcontroller, is not able to drive a load directly. We commonly will use a transistor to drive the load, and trigger it with a microcontroller's output pin.

For MOSFET examples, see our companion article.

Lets use an example. Say we have a 20v dc motor, that requires 500ma of current at load.

The Arduino UNO can output 5v, at 40ma or less. Let's use a 2N2222 transistor. From the spec sheet, we see it can handle 600ma continuously, so current requirements are met. We also see it can handle around 30vdc, so the voltage requirements are met. Looks like a good match.

Being a NPN transistor, the load attaches between the collector and the positive supply, the emitter connects to a common ground with the Arduino.

To prevent the transistor from pulling too much current from the Arduino, we need a resistor between the Arduino output pin, and the base of the transistor. The resistor must be sized to limit current to no more than 40ma, and to make sure the transistor "opens" fully under load. The more current drawn by the load, the more current is needed by the base.

Download spreadsheet with following calculations:

The 2N2222 has a DC gain of about 30, so the current of the load (500 ma) divided by the gain (30) means we need a base current of around 16ma.

If we assume a Arduino HIGH being around 4.5v, and the diode voltage of the transistor is 0.7v, we get a base voltage of 3.8v. The maximum size of the resistor to maintain a 500ma load will be 228 Ohms. We found this by taking the needed base current of 16ma and dividing by the base voltage of 3.8v (and multiplying by 1000). If you go higher, the transistor may not fully open, and the motor won't perform properly. We could go as low at 100 Ohms without exceeding the max current of the Arduino pin (3.8v / 100 Ohms = 38ma), but there's no need to draw the excess current, so keep the resistor value near the max of 228 Ohms to reduce Arduino power consumption, and leave capacity on other pins. The total current supply capability of the UNO is 200ma (per ground) across all the pins.
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