zondag 27 juli 2014

Pi-files: Heartbeat

It has been a bit quite here on Deddies lab's blog. That doesn't mean that nothing came out of the lab. Actually a lot has happened, but I didn't had the opportunity (or was a bit too lazy) to post it here. Since I took a lot from the DIY community, I feel obliged to return also my findings, struggles and results back to that same community. Only then we all can grow!

Last couple of years, I invested most of my (spare) time in the Raspberry Pi platform. I don't think I have to explain anything about this versatile mini computer. Just google around and you will find tons of projects. I myself was attracted at first to the Rpi because of the General Purpose IO's (GPIO) possibilities which can be used to connect simple inputs (switches) and outputs (nothing beats a blinking led!). I was (still am) used to work with Atmel microcontrollers, where also the pins can be configured as input and output pins. So being able to use the same IO functionality but then combined with ethernet, a decent user interface, etc. etc. etc. opened a whole new world of possibilities.

Let's start easy; Sometimes it is difficult to see from the outside of the Pi is running or not. It has some status leds onboard, but when built in a box and stuffed away in a cupboard (like I have) the status leds are not so easy to see. So for that purpose I made a simple heartbeat. It is just a blinking led, but starts automatically when the Pi boots up, so it indicates when the Pi is alive and kicking!

I have a revision A of the RPi in my 'meterkast' (is it really 'meter cupboard'?).  For this heartbeat and some other projects you can read about in other blog posts I made a dedicated interface board. It also has a led which is clearly visible from the outside

This led is connected to pin 16 of the GPIO header, which is called GPIO4. No, this doesn't make sense, and apparently there is a difference between the physical Raspberry Pi names and Broadcom names. I made a Python script (called heartbeat.py) where I can first configure the IO's:

import RPi.GPIO as GPIO
from time import sleep

#display no warnings (on command line)

#use RPi board pin numbers
#set pin 16 as output
GPIO.setup(16, GPIO.OUT)

The 'sleep' module is inserted to make the led blink. The while loop makes the led blink indefinite:

print "Start heartbeat\n"
while 1:


You can run this script from the command line:

pi@raspberrypi ~ $ sudo python /home/pi/gpio/scripts/heartbeat.py &

When you want to run the script automatically after boot up of the Rpi, you have to edit /etc/rc.local:

pi@raspberrypi ~ $ sudo nano /etc/rc.local

#!/bin/sh -e
# rc.local
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
# In order to enable or disable this script just change the execution
# bits.
# By default this script does nothing.

python /home/pi/gpio/scripts/heartbeat.py &

exit 0

Save the file with Ctrl+X. Make sure that the Python script is executable:

pi@raspberrypi ~ $ sudo chmod 755 /home/pi/gpio/scripts/heartbeat.py

You can check if the script is executable if you see the 'x' in the permission overview:

pi@raspberrypi ~ $ ls -la

-rwxr-xr-x 1 root root   261 Jul 21 21:34 heartbeat.py

Reboot the Pi and see the led blink:

pi@raspberrypi ~ $ sudo shutdown -r now

donderdag 29 mei 2014

Motion Detection for 12V ledbar

On an electronic flea market I bought two 50cm 12V (700ma) ledbars. They were quite bright and only cost 6 euro a piece. I still needed a proper lighting solution for my work bench and thought these could perfectly serve that purpose.

With some two components conductive glue I glued them on a aluminum strip for thermal conductivity. A wooden frame prevents to look right into the leds when you enter the room. It definitely gives a nice bright even illuminated work bench.

I didn't want to use a switch to turn the lights on and off. It is just not cool! Recently I bought 10 PIR motion detection sensor modules (HC-SR501) on ebay for only 10 euro (How can they even make that for one euro?). I thought one of these can do the job for me when I approach my bench.

The PIR sensor module outputs 3V3 when motion is detected. Sensitivity and ON time can be adjusted on the module. It operates on supply voltages between 4.5 and 20V so the 12V (1.5A) adapter I need to power the ledbars can also power the PIR sensor. I wanted to use an IRF540 NFET to switch the leds, but this NFET doesn't open up completely with a Vgs of 3V3 which limits the current flowing through the leds. That is why I used a smaller BS170 NFET that can be triggered with 3V3. R1 is a 10K resistor to prevent a floating gate signal. Due to another 10K resistor (R2) at the drain of the BS170 an inverted signal of the PIR sensor is available, so a PFET (IRF9540) can invert back that signal to switch on the ledbars. For troubleshooting purposes I added a jumper to  put 12V directly on the ledbars and a test led (always add a test led!) to see the circuit works properly even if the ledbars are not connected.

 I stuffed everything into a small plastic storage box that I found in the kitchen and made it possible to rotate the whole box to be able to point the PIR sensor towards the workbench. It turned out to be a very nice local lighting solution. I doesn't turn on when I enter the room or walk around, only when I enter the work bench it turns on. Altogether it didn't cost me more then 15 euros, I don't believe you can buy something like this for so little money.

zondag 8 januari 2012

Mystery LED in a box: part 7

My friends were so pleased with my sewing craftmanship that they decided to releave us from our duty. No more morse code, no more assignments...

One day we blinked with our eyes and we found our selfmade wallet filled with a decent amount of dough. Our assigment was fullfilled!

A little trip down memory lane:

Mystery LED in a box: part 0: The suprise!
Mystery LED in a box: part 1: Reconnaissance mission
Mystery LED in a box: part 2: Tin soldier
Mystery LED in a box: part 3: Epromising website
Mystery LED in a box: part 4: Chat me up, baby
Mystery LED in a box: part 5: d2hhdCB0aGUgZnVjaw==
Mystery LED in a box: part 6: So sew me...

Thanks, buddies.... who's next by the way?

zondag 18 december 2011

Mystery LED in a box: part 6

see also: Mystery LED in a box: part 0
see also: Mystery LED in a box: part 1
see also: Mystery LED in a box: part 2 
see also: Mystery LED in a box: part 3
see also: Mystery LED in a box: part 4
see also: Mystery LED in a box: part 5

How do you respond to a sentence like the following:


Anyone? Nobody? ANYthing? The last clue kept us busy for a few weeks. 
Shortly after presenting the world our latest progress we found a rather scary letter in our mailbox:

"All your base are belong to us". Not only one of the most famous internet memes ever but as from now also a big hint to solve our mysterious sentence that should lead us to our wedding gift. Googling it didn't result in a lot of usefull stuff other then a huge amount of odes and also parodies to the subject. After a week of puzzling, googling and trying to tear some usefull information from my friends a little birdy (Thank you!) remerbered my of a mental note that I took during part 2 of the queste. The clue of part 2 ended with the number 64 ("VIERENZESTIG"), which was not intended for that assignment. It seemed a bit lost standing there, but I kept it in mind. Maybe it is usefull here.
Adding '64' to the Google search string 'All your base are belong to us' didn't actually give me something new (except some way too nerdy Microsoft stuff). But hurray, my luck changed when I shortened the string to 'All your base 64'. It showed me various leads to the term 'Base64'. Base64 is an encoding/decoding method that uses a base of 64 characters to encode 8 bit ASCII data. It has various applications and it makes a normal sentence look like it is heavily encrypted. For that it is also used to obfuscate passwords. The Wikipedia site showed with a small example how to decode Base64 encoded data, and manually decoding the first part showed my the first letters of my own name, so I knew I was going the right way. Base64 is not very difficult to encode/decode so there has to be somebody that already made a script for the world wide web. Lucky me!
There was only one thing. Base64 encoding makes a distinction between small and capital letters while Morse code doesn't make this distinction. That was an easy one. It immediately explained the apostrophe ( ' ) characters in the mysterious sentence. A letter followed by an apostrophe means a capital letter, otherwise it is used as a small letter.


(Sanne (That's my nickname), sew a wallet with your names 
and wedding date. Show the proof via the blog...) 

The assignment is a wink to my wife's hobby: Sewing and other sorts of crafting. In part 2 she had to do some soldering on the mystery box, so now it was my turn. And here is the result... And yes, it is geeky and nerdy!

What's next? 

zaterdag 26 november 2011

Mystery LED in a box: part 5

see also: Mystery LED in a box: part 0
see also: Mystery LED in a box: part 1
see also: Mystery LED in a box: part 2 
see also: Mystery LED in a box: part 3
see also: Mystery LED in a box: part 4

I promised in the previous item to provide an update after my vacation. That was in August! Unfortunately my vacation doesn't take more then 3 months (I wish!). 

It took me quite some time to make the mystery box actually listen to me. I was able to tell it stuff with the IR transmitter that I had to build, but it looked pretty deaf. The last hint I got was a little assigment to tell the box 'something':


 I figured out that this 'something' had to be the word 'IETS', which is the dutch word for 'something'. 'IETS' has also the advantage to be fairly easy in morse code. Three dots, one dash and again three dots is all it takes (** *- ***).

Just two weeks ago I found out why me and the box were not on the same level. I made a little mistake with one of the resistors.... 3K3 IS NOT THE SAME AS 33K, IDIOT!
The 2K and 3K3 resistors serve as a voltage reference for the incoming photo transistor signal, and using a 33K resistor resulted in a 4.7V reference instead of the intended 3V.


Having that fixed the box and I renewed our vows and we were finally on speaking terms again. Telling 'IETS' to it with IR remote control waked it up and gave me a new sequence of morse pulses. I quickly hooked up my datalogger to log the sequence and let Matlab crunch the data:


Translated: "Who are your best friends? (in alphabetical order)"

Damn, that looks like a tricky question. This really could cost (or gain) me friends... I took the safe road and picked the names of the people that actually contributed to the wedding present.

But some use their real name and others jotted down their nickname in the card. Some of the guys have actually nicknames that are used so often, their real names are already long forgotten (Bart? And who's Frank?). So multiple options here:

Regardless the right answer it promised to be a challenge to send this huge morse code sequence manually, although I realized that is exactly what they did back in the days in WW2. But then they didn't had microcontrollers like we have now so I followed Deddies Labs slogan ("Because anything deserves a microcontroller") and start putting together a morse code generator.

That worked! A little bird had told me in the meantime what the most likely answer was to the friends question, and finally the mystery box gave me the next morse sequence. Again twice as fast as the previous clue which was also double as fast as the one before that....
Inevitably the datalogger needed some more tuning since the last upgrade which boosted up the sampling frequency to a whopping 40Hz (!!!) proved not to be fast enough (C'mon guys, cut me some slack here). I actually compressed the data before storing it to the USB stick and decompressed it with Matlab (I will explain this later on in a different topic). It is now so freakin' fast that I myself don't even now how fast it is. I probably can expect some phonecalls from the CERN...

This clue is probably also the last clue the mystery box will give me, a running led sequence after the hint gives me the impression that its job is finished. I am shedding no tears, it is still electronics and it can't withstand salty water very well:


What the hell? Is this my final hint? This is not human readable. No easy "Congratulations, the present can be picked up at the trainstation in locker 1306"? Did I read the morse code right? Yes, I think I did! Did something went wrong with compressing the data or did Matlab had a bad day? Not likely.

Chuckles of recognition of some of my friends gave me definitely the idea that I got the clue right. As you all can understand, more to follow...

see also: Mystery LED in a box: part 6
see also: Mystery LED in a box: part 7 

maandag 8 augustus 2011

Mystery LED in a box: part 4

see also: Mystery LED in a box: part 0
see also: Mystery LED in a box: part 1
see also: Mystery LED in a box: part 2 
see also: Mystery LED in a box: part 3

Days passed by since we fulfilled our last assignment considering the mystery LED box without any news. Did we do it right? Were we missing something? Last week the uncertainties suddenly vanished with a envelop that we found on our doormat.

In the envelop we found some interesting parts: a micro switch, an IR led, and a BP103 phototransistor. I rushed to the website we found in the previous clue and there we found a new briefing. The 'Grande Finale' was about to take of...

Again I had to add stuff to the already pretty stuffed up board and upload a new hexfile to the Attiny. I was asked to build an simple IR transmitter and giving the Attiny the capability to receive IR signals. Instead of one led the board now needed three leds.

The next evening I did my magic and a couple of hours later the mystery box was blinking again...

It started with a running light, followed by 1 minute of sequential blinking of the middle led, finished by the 3rd led turning on and off only once. Nothing after that, you could almost hear the Atmel sleeping :) In the video you can find the BP103 photo transistor in the box on the left.

Diligently I hooked up my ever so useful datalogger! Just before I started recording the new sequence like I did with the previous clues, my attention was caught by the middle led..... Damn! Rat bastards...... the sample rate of the led sequence was definitely faster then 4Hz this time and my datalogger is not capable of recording any faster. And reading the morse code with the naked eye is definitey out of question at those speeds. I knew I should have kept my mouth shut about this bug (or blog about it). Me and my big mouth!

My friends' goal was definitely to slow down the progress solving the mystery box, apparently I was going to fast for them. Now I had to (quick) fix the datalogger first. And we were about to leave for vacation in a couple of days, were I was forbidden to even think of electronics or dream of Atmels. I agreed with myself to speed up the datalogger and get at least the next clue out of the mystery box before packing my bags.

From the datalogger's sourcecode I removed everything unnecessary that could slow down the recording. Wow, I did some realy awful programming two years ago. 4 hours and a lot of deleting and rewriting later I managed to get the datalogger to record with an astonishing speed of at least 40Hz. I didn't try to make it faster, a tenfold increase seemed fine by me. I figured my friends not to be that big of assholes... Luckily I was right. After recording and some minor changes to the Matlab script the next sentence popped up:


Like I already suspected with the IR led and phototransistor the box was now capable of also 'listening'. It 'asked' me to say 'something' to him/it. This 'something' I still have to find out. I really have to pack my suitcases now...

As you probably already have noticed, a project like this kind of grows on you. Like my 1 year old son it finally starts to listen and I start to understand its babbling. I hope I won't mix up the two, and find myself poking a soldering iron in my son's eye while the mystery box is getting a bath.

More after my vacation...

see also: Mystery LED in a box: part 5  
see also: Mystery LED in a box: part 6
see also: Mystery LED in a box: part 7

zaterdag 16 juli 2011

Mystery LED in a box: part 3

see also: Mystery LED in a box: part 0
see also: Mystery LED in a box: part 1
see also: Mystery LED in a box: part 2

Still we don't have the contents of the wedding present that was given to us on our wedding party. Along the way we found clues telling us to exentend the electronics board with a pushbutton and most recently to fill all 128 bytes of the EEPROM with the hex value '0x03'.

To get to the EEPROM I added a 10 pins ISP header to the board to be able to connect it to my programmer. This gave me also the nice opportunity to read the fuse and lock bits to anticipate for any other surprises. Hmm, no surprises here (was I thinking too difficult again? Was I disappointed?), the fuse and lock bits were left alone and still had their default value. I also made a backup of the EEPROM and Flash memory to fix any possible screw-ups.

I used Codevision to read the EEPROM and changed it as requested. Yeehaa, a new Morse sequence!


(the '*' were actually filled in but are not really relevant here)

After congratulating us with the achieved result so far we were presented a website for the next clue. Here the clue ended with a seemingly harmless reference to the coolest bumper sticker ever that hangs on the wall of Deddies Lab. Note taken!

So, a website. The tips&tricks section on the website gave us a link to the wikipedia site of morse code. We could have used that some time ago! Funny...

We were told to make a picture of the mystery box with today's newspaper to prove that the cube was still intact. Okay, I maybe broke it a week ago... but it is fixed now. The picture below will lead us further on our quest as promised on the website.

It is obviously that somebody is watching our moves. I suppose we have to be carefull with what we say the weeks to come. Hang on...

see also: Mystery LED in a box: part 4 
see also: Mystery LED in a box: part 5  
see also: Mystery LED in a box: part 6
see also: Mystery LED in a box: part 7