Author: Gerald

Diplom-Informatiker (DH) in Darmstadt. Ich blogge über Entwicklung, Internet, mobile Geräte und Virtualisierung. Meine Beiträge gibt es auch bei Google+ und Facebook.

Wordclock 0.4

I did some updates to the software of the wordclock. It couldn’t really cope with interference, and since it relies on updates from the DCF77 receiver every minute it doesn’t really work as soon as something interferes. I was a little surprised how much the signal is affected by everyday things. TVs, for instance, at least the CRT kind, which is still widely used. My main problem turned out to be the lights of my aquariums, which are neon tubes. They too affect the radio signal, which I confirmed with a “normal” radio controlled clock.

To account for these issues I modified the code to display the time from the Arduinos internal clock. This internal clock is not very accurate, from what I gathered on the Internet it is off by a couple of seconds after only a day or so. For that reason I use the radio clock signal to set the internal clock when it gets a clean signal, which should be every day at night when all interfering sources are turned off. That way the RTC chip i mentioned earlier in this post is not really necessary.

I updated the main article about the clock to reflect these changes, the new software is available for download there as well.

Controlling the boats motors from Android

So, I finally managed to get the basics done and put them together. First were the ESC for the motors. I had ordered two Turnigy 30A ESC for brushed motors from HobbyKing and it took “only” six weeks for them to be delivered. I guess it was my fault, ordering right before the chinese new year, when nobody seems to work for the next two weeks. At least neither my order was processed nor my questions were answered by the support. Anyway, they arrived eventually and I connected them to the motors, the battery pack and the Arduino. Continue reading Controlling the boats motors from Android

Keep serial pins free!

This weekend I did some final troubleshooting on my first wordclock. I had the problem that every time the display was updated all LEDs flickered a little. Very annoying, especially when there is no change.

Finally it hit me: I had connected the 74HC595 chips to the pins 1, 2 and 3. I guess I just wanted to “start” somewhere. What I didn’t account for, is that Arduinos serial port is accessible via pins 0 and 1. They are even labeled with RX and TX. So, everytime I sent data to my computer over the serial line it also went out on pin 1, which is connected to the 74HC595, hence the flickering.

Long answer short: Don’t use pins 0 and 1. Except for serial connections of course.

Improving accuracy

Thanks to the readonly old Arduino forum I noticed only today that the author of the DCF77 code I am currently using published an update, nearly a year ago.

He wrapped it in a nice library, which makes it a lot easier to use. Sadly it doesn’t work on version 1.0 of the Arduino UI, so I reverted to version 0022 for now. There are newer “old” versions of the UI, but I had this version still installed.

This is the example from the library:

#include "Dcf77.h"
 
Dcf77 dcf77(0); 
 
void setup() {
Serial.begin(9600);
}
 
void loop() {
const char *v = dcf77.getDateTime();
if (strcmp (v,"DCF77POLL") != 0) {
Serial.println(v);  
}
}

The library takes care of parity and plausability checks, so I don’t have to worry about that anymore. The downside is that it produces the current time far less frequent than the code I’m using now, but when it returns one it is correct.

I’m still leaning toward adding a realtime clock to the clock. This way I can rely on the RTC for the current time and correct it now and then when I get a signal from the DCF receiver.

Circuit board for the wordclock

Yesterday I was playing with Fritzing to create a circuit board for the wordclock. Building it on the breadboard was easy, but the auto routing on the PCB-layout drove me nuts. Today I tried it again, loaded the file, repositioned the components on the circuit board a little and guess what … it worked on the first try. This is how the circuit board in the next version of the wordclock may look like:

It is designed for an Arduino Mini Pro, which is by far the cheapest Arduino variant I could find and which is sufficient for this purpose. U1, U2 and U3 will hold the 74HC595 ICs, J3, J4 and J5 will connect the LEDs. J2 is the connection for the DCF77 receiver.

I guess next I’ll have to learn how to etch my own circuit boards.

Wordclock finished

Yay, my Arduino based wordclock is finally finished.

Since it currently seems to be impossible to embed a YouTube video without it loading tracking scripts the video can only be viewed directly on YouTube.

It uses a DCF77 radio receiver to get the current time and an Arduino to interpret it and control LEDs to show the time.

You can find the full writeup of the clock on this page.

Breakthrough

This evening I managed to get a breakthrough while I was working on the wordclock. The clock kept showing a completely wrong time now and then, followed by the correct time a minute later.

So I loaded the test program for the DCF receiver again and monitored the output on the serial console over a longer time (one or two hours or so). I noticed that the receiver actually gave incomplete information once in a while. To rectify this I did two things: Continue reading Breakthrough