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?


Arduino Time Libraries

Arduino DST Solution

Friday, August 25, 2017

Arduino / Relay Interference


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.


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.


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:


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


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.

Saturday, June 24, 2017

ESP8266 BME280 Weather Station

One of our favorite new toys is the ESP8266 WiFi module. A very powerful microcontroller in it's own right, it's easily programmed with the Arduino IDE, and uses the same code we have come to know and love.

Now pushing data to web server!

So lets start:

We received a NodeMCU ESP8266 microcontroller and a BME280 Temperature / Humidity / Barometric Pressure module from IC Station.

Both the ESP8266 and the BME280 are 3.3v devices, so no level shifting required. The BME280 is an I2C device, so I connect SCL to D1 on the ESP8266, and SDA to D2. VCC goes to 3V3 and GND to GND. That's it for wiring.

I need to add the ESP8266 to the Arduino IDE, so head over to http://arduinotronics.blogspot.com/2017/03/arduino-esp8266-wifi-on-cheap.html for a quick tutorial.

You will need two libraries from Adafruit, both the BME280 and the Sensor libraries - https://github.com/adafruit/Adafruit_BME280_Library

I used their example sketch, but modified the metric outputs to American, and added calculations for Dew Point and Heat Index.

Once the board is installed, you are ready to upload the modified sketch: https://pastebin.com/rhkJGApY

The output of the serial monitor should look like this:

Our next step with this is to push the data to our new IOT web / database server, with live charts, gauges, and database storage. Stay tuned!

Check out all our videos on Youtube!

Friday, June 2, 2017

Logic Level MOSFETs, IRL or IRF?

If you need to switch a dc load, a MOSFET is a very useful component. Typically carrying much more current than a standard transistor, and better performance characteristics, like a high impedance gate that draws very little current. BJT's are current driven devices, MOSFETs are voltage driven devices.

Not all MOSFETs are the same, and too many Arduino sites show the IRF series MOSFET. The IRF series require 10v (VGS = 10.0 V) at the gate to fully open at anywhere near rated loads, so we use the IRL series. Any logic level N-Channel MOSFET (VGS = 5.0 V) will work, and look for the lowest RDS(on) (Ω) resistance you can practically find, to limit heat buildup. Connect your DC load between + and the Drain (D) of the MOSFET. Connect the MOSFET Source (S) to ground, or negative terminal of your voltage source. We add two resistors, a 10k Ohm from the MOSFET Gate (G) to ground to ensure turnoff when Gate signal is removed, and a 125 Ohm resistor between the Arduino output and the MOSFET Gate (G). This protects the Arduino pin from too much current draw. The value is determined by the voltage of the Arduino pin (5v) divided by the max current we want to allow (40ma). The IRL540 shown has a built in snubber diode that prevents motor flyback from damaging the MOSFET or Arduino. The Arduino sends a HIGH signal to turn on the MOSFET, a LOW to turn it off, and can also use PWM (analogWrite on an appropriate pin) to control motor speed, lamp brightness, etc.

Thursday, May 25, 2017

"Clear All" Checkbox Script

Ever need to have a "clear all" check box, and have any of the other check boxes clear the clear all? Well, we needed that, and came up with a solution for your coding pleasure. It's in PHP, but can be done in HTML as well. It uses a bit of javascript in either to make the magic happen.

Code: https://pastebin.com/kP701jQ4

Wednesday, May 3, 2017

Convert a UPC-A to a GTIN-14

More and more I'm having to use GTIN barcodes instead of the old UPC-A bar codes. I needed a way to automatically grab the UPC-A bar code number from our database, strip the check digit, and generate a new GTIN-14 bar code on the fly, with a newly recalculated check digit. This is done in PHP, so take a whack at it and have fun! I'm still investigating how to produce bearer bars.

The trick to generating a check digit is list the 12 digit UPC-A with two zeros as a prefix, and starting with the first position on the left, mark the numbers as the Odd and Even positions, leaving off the last digit (check digit).

00  6631    2102    3756

Add all the Odd positions together :19
Add all the Even positions together: 17

Multiply the Odd total by 3: 19*3=57

add the Odd and Even totals together: 57+17=74

If a multiple of 10, check digit is 0. In our example case it's not, so if not a multiple of 10, Subtract from the next higher multiple of 10: 80-74 = 6

6 is the check digit. Now add a 01 prefix in front and you have a GTIN-14 compatible bar code.

01 0066312102375 6


Tuesday, April 25, 2017

Display a TextBox only when a Radio Button is Checked

I was working on one of my websites this week, and needed the ability to allow the user to input some text only when a certain radio button is checked, and make the TextBox go away when another radio button is checked. All the TextBox's are hidden on page load, then activated when the "Other" radio button is checked. I also use placeholder="" to give the user some idea of what goes into the box.  After a few tries, I got it working and figured, if I needed this, others may as well, and to save you some time and angst, here is my code. Works well in HTML or PHP (just add echo' ... '; pieces).


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