# Selfmade stackmat display



## fw (Aug 2, 2008)

Hi guys,

since the original stackmat timer is _way_ to expensive in my opinion, I am trying to build my own one. It runs without a PC, just the stackmat and a battery, like the original one. I am planning to implement all features of the original and maybe some additional stuff like average calculation or maybe storage of times in (non-volatile) memory (even after power down).

Please have a look at my prototype and tell me what you think.. I would be happy if someone has suggestions and ideas for features 

http://www.youtube.com/watch?v=_ZmVrjTTpVE

(Of course the display LEDs will be much bigger in the final version! Before you ask: The first digit shows the button status and is just for debugging purposes, of course that will be indicated with LEDs (red and green, like on the stackmat timer for example) in the future)

-- Flo

(If you wonder: The display costs about 1 to 2 dollar per digit, the microcontroller and its periphery about 3 dollars.. I think it is possible to build a complete functional stackmat display with a nice case for less than 15 dollars total).


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## nitrocan (Aug 2, 2008)

can you tell us how to build it? what to buy? i dont want to spend a bunch of money to buy the original display.


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## 36duong (Aug 2, 2008)

Looks nice, But maybe The Numbers could be a bit bigger, and I don't get the red numbers...


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## fw (Aug 2, 2008)

Like I said in the first posting, the display will of course be bigger, I am thinking about (at least) 5cm digits.

The first digit is the button status (for example "4" means left button is pressed, "5" means right is pressed, "6" means both are pressed, "1" means both are pressed and timer is ready, etc.). That will be removed later and is just for debugging at the moment. (The second red digit is the minute of the time (yes, stackmat timer can do up to 10 minutes (-1 sec))

Of course, when (or if ) I am finished, I will give a detailed description of what to buy and how to build it on your own. Anybody with some basic soldering skills can do it.


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## Pedro (Aug 2, 2008)

dude, that is cool!

if you could make a tutorial it would be awesome

I'm an electrical engineering student, so I would surely build one (or more ) of those


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## DavidWoner (Aug 2, 2008)

Pedro said:


> dude, that is cool!
> 
> if you could make a tutorial it would be awesome
> 
> I'm an electrical engineering student, so I would surely build one (or more ) of those



shouldn't you be able to build one on your own then?


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## Pedro (Aug 2, 2008)

Vault312 said:


> Pedro said:
> 
> 
> > dude, that is cool!
> ...



well, maybe...I'm just starting the course (finished the 3rd semester), so I don't know lots of technical stuff yet


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## DAE_JA_VOO (Aug 2, 2008)

Very VERY cool. I would DEFINITELY be interested in something like that. Any chance you'd be willing to give us a schematic?


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## fw (Aug 2, 2008)

yes, sure, just give me some time to finish it.. I will publish schematics and source code then...


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## Zigosity (Aug 3, 2008)

Hehe, that's pretty sweet. Post a schematic and source for the controllers, and I'll be building myself one of those for sure 8).


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## DAE_JA_VOO (Aug 3, 2008)

Awesome, thanks a lot man


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## fw (Aug 3, 2008)

what would you say how big the display of the original timer is? about 2 inches (height)? Anybody who got one of those displays and who could check for me? I like green or blue much more than red as LED color.. what do you think?


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## nitrocan (Aug 3, 2008)

red looks more alive, so its more exciting! the display is probably 2 inches. (i dont have one im just guessing) but it doesn't matter as long as its visible from 10 meters away.


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## studzien (Aug 3, 2008)

Original display has about 6 cm digits, so a bit more than 2 inches.
I've measured the old type of display, but I think that doesn't make a difference.

I'm looking forward to seeing your solution too!


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## Swoncen (Aug 3, 2008)

nice! I will also build one if you told us what to buy, etc. =)


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## Pedro (Aug 3, 2008)

the new model display has 5.6cm numbers


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## nitrocan (Aug 3, 2008)

im gonna explode soon if you dont tell us how to do it !


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## DAE_JA_VOO (Aug 3, 2008)

nitrocan said:


> im gonna explode soon if you dont tell us how to do it !



Me too!! Hahaha

Schematics!! We want schematics!


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## fw (Aug 3, 2008)

hehe, sorry guys, you will have to give me some time  But I will publish everything when its finished, I promise. There is a problem though. The software that I am writing needs to get transfered to the microcontroller. Now, there are basically two ways which I can currently think of: 1.) I do it and send the programmed microcontorller to you (which is OK for me, if its just 5 oder 6 people who are interested), 2.) you have to do it yourself, which means you do need an atmel programming adapter. The programming itself is not hard, there is ready-to-use software for that. So, while you are waiting for me to finish this thing, you could go read up about atmel ISP programming adapters (that are the cheap ones, you can build one your own with less than 2 dollars. Dont buy the original ones from atmel, they have way to many unnecessary features and are very expensive). Be patient


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## Pedro (Aug 8, 2008)

any news? if you tell us which capacitors and resistors to use, it would be good


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## fw (Aug 11, 2008)

Pedro said:


> any news? if you tell us which capacitors and resistors to use, it would be good


No, no news so far, sorry. I will do my best if I have some free time soon. You will need five 7 segment LED displays with (important) common cathode, NOT common anode. Then you will need some (at least 5, but order some more, they are cheap) 1µF electrolytic capacitors, a socket for the stackmat cable (I think its 2.5 or 3.5mm), an Atmel Atmega 88 Microcontroller, an Maxim MAX232 Level shifter, a Maxim MAX7219 Display Driver (which is not really necessary, you could multiplex the displays yourself, but that requires some software modifications), some 10K resistors (at least two I think), some 100 nF ceramic capacitors (at least 5 I think), some LEDs (pretty much doesnt matter what color or what type, just get the appropriate resistors for them (datasheet!)), some buttons (for stuff like "delete time", "save time", etc.), some switches (power switch, I like toggle switches), some diodes (4004 for example), an 7805 voltage stabilizer (looks like this, get the left one))...

Well, I did not make a schematic yet and I am sure there is something missing... I recommend if you cant wait, order the 7 segment LED displays and wait for my tutorial before you order the other stuff... The 7 segment dispalys need some searching.. Some stores are quite expensive.. Some are quite cheap.. Usually, the red ones are the cheapest.. I found some nice black ones with red LEDs, about 4cm height, for less than a dollar... Thats a good price


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## fw (Aug 15, 2008)

I took some time to draw a schematic today (file is attached).

This is just a first version! I am sure there are some mistakes that I will correct later when I notice them. The ISP socket is only necessary if you intend to program the microcontroller yourself (and of course, this circuit wont do anything without a software on the controller, which I will publish later).


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## Pedro (Aug 15, 2008)

thanks 

I thought it would be simpler...

but looks like you have a lot of "extra stuff", like buttons and status leds, average calculations and so...

I wanted to do just a display, only to show the time, like the original one...
would be much easier, right?


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## hisoka (Aug 15, 2008)

you used eagle cad software?


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## nitrocan (Aug 15, 2008)

dude, what is that?  could you simplify that?


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## fw (Aug 15, 2008)

well, you dont need the ISP socket and you dont need the LEDs and buttons. If you have a power supply, which gives you exactly 5 volts, you dont need the power supply circuit either.

I know, it looks a bit complicated, but trust me, it is not that hard. The Power supply circuit is very useful. You plug anything which gives you about 9V or higher (a battery, some old mobile power adapter, anything you like, doesnt matter) and you get exactly 5V output (which is the needed voltage for the microcontroller). The MAX232 adapter is the "heart" of this thing, it regulates the voltage the stackmat gives you (a "RS232" signal, the same every serial line a computer uses) and converts it down to 0V/5V, which the microcontroller can understand.

Dont be scared. I will create a display and make some pictures, you will see, its not that much hardware. Dont worry about the costs either.. All together, this circuit costs about 15 to 20 dollars, depending on the price of the LED displays..

And yes, the CAD software is Eagle.


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## nitrocan (Aug 15, 2008)

well most of us don't even know what those things are, can you make a list of what we will buy, and a video tutorial maybe?


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## fw (Aug 15, 2008)

well, I am not going to tell you, that you can rebuild this thing without any knowledge in electrical engineering, but I promise you, that its not as hard as it looks.. I will see what I can do


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## hisoka (Aug 15, 2008)

can you make this a stand alone timer? that is, you do not need stackmat for it to display your times...


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## 36duong (Aug 16, 2008)

I have seen the schematics, looks professional. Are you a practising engineer? 

I have some queries, can we use say 4 x AA batteries making 6 volts, instead of the 5 volts indicated, How long would battery like this last? 

Second query, using ISP socket how do you download the file into the microcontroller.

Can you post a Bill of Materials? What do you use for the prototype PCB?

Thanks in Advance


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## hisoka (Aug 16, 2008)

i think he used pcb 401 for his prototype, but of course you can make your own pcb layout, and fabricate your own pcb


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## fw (Aug 16, 2008)

Thanks, but no, I am not a professional.. I study computer science, but actually, I just started 2 or 3 months ago with microcontrollers (that should be an indicator to you, that it does not need years of experience to build (or rebuild) such stuff).

I am not planning to build a stand alone timer, sorry.. Not yet.. BUT, hm, nice idea.. Since I already know the stackmat protocol (the way the stackmat communicates with the stackmat display), that would be a nice idea for a next project.. I could build a stand alone timer, which can communicate with my selfmade display AND with the original display (since they "speak the same language")  But first I want to finish this thing, and this is "display only (with some goodies)" 

The prototype board you can see in the video is in german called "lochraster", its a special type of board with holse in a grid and contacts on the back, especially for "rapid prototyping", its not etched or something like a real pcb layout.. Here is a bigger bicture..

I dont know how long battery will last.. I will try this when its done.. I hope its long enough.. The microcontroller itself needs exactly 5V or a power regulater which creates 5V from anything higher than about 7.. You could use something like this I suppose.. But I am not 100% sure..


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## hisoka (Aug 17, 2008)

i think it is better to use the max232 voltage regulator, it is more reliable, it is used for stability of the circuit especially if you are using microcontrollers.


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## xentall (Mar 12, 2011)

Hi! Can u publish the communication protocol (data format)?


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## Stefan (Mar 12, 2011)

His documentation describes it: http://hackvalue.de/hv_atmel_stackmat


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## blackzabbathfan (Mar 12, 2011)

hey this is great. if i ever want to buy a display i would probably buy a stackpod, but you know, this looks like a really fun and i might build one


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