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Step 53: Software: Interrupt routine

The heart of the LED cube code is the interrupt routine.

Every time this interrupt runs, the cube is cleared, data for the new layer is loaded onto the latch array, and the new layer is switched on. This remains on until the next time the interrupt runs, where the cube is cleared again, data for the next layer is loaded onto the latch array, and the next layer is switched on.

The ATmega32 has 3 timer/counters. These can be set to count continuously and trigger an interrupt routine every time they reach a certain number. The counter is reset when the interrupt routine is called.

We use Timer2 with a prescaler of 128 and an Output Compare value of 10. This means that the counter is incremented by 1 for every 128th cpu cycle. When Timer2 reaches 10, it is reset to 0 and the interrupt routine is called. With a cpu frequency of 14745600 Hz, 128 prescaler and output compare of 10, the interrupt routine is called every 1408th CPU cycle (128*11) or 10472.7 times per second. It displays one layer at a time, so it takes 8 runs of the interrupt to draw the entire cube once. This gives us a refresh rate of 1309 FPS (10472.7/8). At this refresh rate, the LED cube is 100% flicker free. Some might say that 1300 FPS is overkill, but the interrupt routine is quite efficient. At this high refresh rate, it only uses about 21% of the CPU time. We can measure this by attaching an oscilloscope to the output enable line (OE). This is pulled high at the start of each interrupt and low at the end, so it gives a pretty good indication of the time spent inside the interrupt routine.

Before any timed interrupts can start, we have to set up the Timer 2. This is done in the ioinit() function.

TCCR2 (Timer Counter Control Register 2) is an 8 bit register that contains settings for the timer clock source and mode of operation. We select a clock source with a 1/128 prescaler. This means that Timer/counter 2 is incrementet by 1 every 128th CPU cycle.

We set it to CTC mode. (Clear on Timer Compare). In this mode, the counter value TCNT2 is continuously compared to OCR2 (Output Compare Register 2). Every time TCNT2 reaches the value stored in OCR2, it is reset to 0 and starts counting from from 0. At the same time, an interrupt is triggered and the interrupt routine is called.


For every run of the interrupt, the following takes place:

1) All the layer transistors are switched off.

2) Output enable (OE) is pulled high to disable output from the latch array.

3) A loop runs through i = 0-7. For every pass a byte is outputed on the DATA bus and the i+1 is outputed on the address bus. We add the +1 because the 74HC138 has active low outputs and the 74HC574 clock line is triggered on the rising edge (transition from low to high).

4) Output enable is pulled low to enable output fro the latch array again.

5) The transistor for the current layer is switched on.

6) current_layer is incremented or reset to 0 if it moves beyond 7.

That's it. The interrupt routine is quite simple. I'm sure there are some optimizations we could have used, but not without compromising human readability of the code. For the purpose of this instructable, we think readability is a reasonable trade-off for a slight increase in performance.

<p>WOW - 5 million views.</p><p>I think it's some kind of record! LOL!</p>
Hi, Where do i buy all that stuff for 69 dlls? Thanks
<p>thats projects its great! Im looking for all the stuff and making time for doing! please continue doing amazing thing. :)</p>
<p>hi, really great instructable, kind that inspires people.</p><p>This code, cube[5][3] |= (0x01 &lt;&lt; 4);</p><p>Hex01 bit wise move 4, or with a 2d array, I can't get my head around it.</p><p>Plz, a more detailed description will save me from more tablets, cheers</p>
<p>Made it!!</p><p>Thank you for the great instruction!!</p>
<p>Your print looks very neat. Mine is very messy.</p>
<p>Wow, how do you get your trace wires so straight and the perfect length?</p>
<p>I measured 1, and cut them all to the same length at once...</p><p>And alcohol-free-february also did the trick ;-)</p>
<p>Hahaha nice work!</p>
<p>Nice job. Many never get their hand wired boards working! Nice and tidy job too.</p>
<p>Do you have a list of components that that board required?</p>
<p>Thank you for your guidance chr..</p>
<p>i am selling most of the components needed from Futurlec. I decided to do the Tindie kit instead. You can find my list of parts (less 512 LEDS) and further info in the classified sale section here: </p><p><a href="http://www.instructables.com/community/Major-Parts-KIT-for-8X8-CUBE-LED-from-Furturlec/">http://www.instructables.com/community/Major-Parts...</a></p><p>I am offering this at a discount and Priority mail within the US. </p><p>thank you</p>
<p>What's the purpose of the address bus?</p><p>And can all of the cube or generally any number of IO's can be runned with only 3 pins by making layers of shift registers?</p>
<p>Is it possible to just switch out these same color LED's for some RGB LED's without changing anything else, apart from the code?</p>
<p>I understand that RGB LEDs have 4 pins, and this may be change the layout of how cube is soldered. How much harder am I making this project by deciding to use RGB LEDs. This is my first LED cube so I don't want to get in over my head.</p>
<p>hi</p><p>i need a help for connecting program (3d8s alpha ) to arduino uno </p>
<p>If we want to replace all transistors, for cathode riser, like Đ&ocirc;ng Phạm post, we can use ULN2803. If we are anode riser, TD62783 is the replacement for ULN2803.</p>
<p>Great Tutorial. Thanks</p>
<p>hi<br>thanks for this nce tut. </p><p>can any one tell me if i can use SN74LS574,HD74LS138P instead of 74HC574,74HC138 and im using arduino uno <br>thanks alot<br></p>
<p>hello all of you, I have an idea to replace 16 BJT by ULN2803, it would save up for your area, and it works very tot.Toi did 2 cube leds and it all works fine however, I did not design the RS232 connection on my circuit. and here are some pictures about it:</p>
<p>Hi DongP1, I am so like the Cube and I want to make it and give to my girl friend as a big surprise. Can you send all schematics ,programs and other files to me . Thans so much.</p><p>My e-mail address: dongliang.ma@matrixopto.com </p>
https://drive.google.com/file/d/0BzXbfPpoHKV5eWQxU1VQODZhTTA/view?usp=sharing
<p>Hey guy, if i use STK500 device to set up for atmega32 then plug it to the board , so, can i remove RS232 and AVR Isp?</p>
<p>sir, i have successfully made my cube, now the problem is with the code... im using arduino uno and the code given in this article i.e for arduino user is working fine for me... but other codes which are used for AVR is not compatible with aduino ? does coding for both arduino uno and AVR are different ?</p><p>i got a error as &quot;compilation terminated </p><p> exist status 1</p><p> error compiling &quot;</p><p>if there is solution for this plz post . </p><p>and the code in the link which u gave is compatible with arduino uno ? </p><p> Thanks :)</p>
<p>You likely need an older, or possibly a newer copy of the IDE.</p>
<p>sir presently im using latest version of IDE i.e 1.6.7</p><p>can i know the the exact version of IDE ??</p><p>and sir how can i make others codes compatible with IDE?</p><p>Thanks :)</p>
mail me.. 233himanshu@gmail.com
This is here. https://drive.google.com/file/d/0BzXbfPpoHKV5eWQxU1VQODZhTTA/view?usp=sharing and don't need chager in program .
<p>Hi Phamd4 , thank you so much. I have another question, I can not open the CUBE schematic and pcb files with Protues Desing Suite 8.0 , my computer is Win 7 system. whether the version of the Protues is not matching? Can you help me .</p>
<p>You can use even less space using SMT 2N2222 type transistors. My board will take either.</p>
Can you please kindly send me the circuit and diagram.
<p>The circuit diagrams for this project are in this instructable.</p>
My email address is sisirroy777@gmail.com
<p>Hello DongP1, <br>Can you share a more clear schematic how did you used the ULN2803 and explain what changes have you done to the code ?</p><p>Thanks</p>
You don't need changes in code
<p>OK you, I'm very fun when help you. You can use Proteus to open file schematic and PCB, and i did fixed code. all in here:<br>https://drive.google.com/file/d/0BzXbfPpoHKV5eWQxU1VQODZhTTA/view?usp=sharing<br>when you use atmega32 you must set fuse for it. <br></p><p>and when you solder PCB solder you should note carefully and did not miss any legs, as this is the second circuit face, you can also book for someone trained to do it to ensure circuit reliability. And my final non-electric circuits become restricts motherboard area, it absolutely does not affect the led. And can not forget that it is a 5V supply. Wish success. I look forward to seeing your circuit here.</p><p></p><p>Inside the downloaded folder: principle diagram, schematic print, inside a simulated 3d opened by Proteus, the revised code with external hex file, inside the code can edit custom and standard you, use WINAVR (recommended recommended). and images to set the fuse for ATmega32.</p>
<p>Hi!!<br>Do you know hoe to flash the EEPROM of Arduino just like we do in normal non-arduino boards..<br>i.e. we flash .eep file directly into the micro controller.. do you know any similar or equivalant thing in Arduino...?</p>
<p>I sorry you, because I do not use Arduino, so I did not go through the difficulties you face, but you can read more online material on its use. I can only help you in terms of hardware. Good luck. I believe you will succeed! : D</p>
<p>Thnx for replying!<br>I got a solution for it already!</p>
<p>Hello, </p><p>Now I got it. The idea to use the ULN2803 is to avoid using transistors correct ?<br>What do you mean that I need to set the fuse for the ATMEGA32 ?<br>I will be using arduino board, either Nano or mega. </p><p>Thanks for your reply </p><p>Jose </p>

About This Instructable

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Bio: I like microcontrollers and LEDs :D
More by chr:Reverse Engineering: RGB LED Bulb with IR remote Reverse engineering: USB controlled home automation hack LED Cube 8x8x8 
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