30 replies to this topic

[Stanislav Husár]

Hi Mario, If I have to solder SMD ICs, that will be problem. ICs with DIP package should not be very problematic to solder for me. Transistors are not so small, I think that it won't be problem to solder them. And price? If it will fit into maybe 10 €, no problem. Are those transistors so expensive ?

[Mario Vernari]

I have no SMDs in my mind, also because I'd like to test the circuit on the breadboard, so SMDs would be hard for me too.
Your target has many constraints, so it's much a challenge than a concrete project: that's why I love it!
Just to wrap it up: transistors are mandatory because the currents involved, but a single transistor shouldn't cost more than 1 Euro. One Euro each is even too much.
I guess to be able to fit all the parts within the 10 Euro constraint, however I won't count PCB and related materials. My viewpoint is that for 1-3 pieces a PCB is not worthwhile.
The only constraint (if it was) I don't think to honor is the overall size: there are many parts to glue together, so that you can't consider to fit in a stamp-size PCB.

Please, let me a couple of weeks more: I'm leaving for a short holiday (finally!), then I'll catch the parts for creating the circuit.
Sorry for the long time taking for me...
Cheers

[Mario Vernari]

Okay, the circuit seems working fine. Sooner I'll post some instruction on how to create it. Cheers

[Mario Vernari]

Here is a brief video of the resulting circuit. Please, since the solution is pretty-complex, tell me whether you are still interested. Cheers

[Stanislav Husár]

Hi Mario, Yes, I am still interested.

[Mario Vernari]

It took me a lot of time the description of the circuit, but finally I've finished it. http://highfieldtale...driven-via-spi/ Please, feel free to ask whatever you need. Cheers

[Stanislav Husár]

Hi Mario, Thank you for your time. Sorry, but I still quite don´t understand the circuit. In the LED Driver section, there are transistors for driving rows. But, what I don´t understand, is why there is that fourth transistor, with collector connected to E0. I don´t understand, what does that E0 do. Can you explain me it? And second thing. Rows would be driven by BC639. And columns? Where I have to connect LED columns ? EDIT: I just realized, that on the same scheme(with BC639 for rows), there are also BC640s to drive columns. So, If I understand it, I have to repeat that pattern with E0 4 times(I attached a picture, which shows how I mean it)?

Attached Files

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[carb]

It took me a lot of time the description of the circuit, but finally I've finished it.
http://highfieldtale...driven-via-spi/

Please, feel free to ask whatever you need.
Cheers

Nice job Mario,

Very Detailed.

Thanks,
Chuck

[Mario Vernari]

Stanislav, I strongly suggest to check how much current your leds need, before thinking to start with the circuit. Connect just one led of the matrix (assuming you're using the same as the old photo), choose a DC power source (e.g. a battery or else) and evaluate several resistors. For instance, choose three resistors: one for 5mA, one for 10mA and one for 20mA. You should only *estimate* the current: no precision at all. If your led shines enough with just 5mA or less, the circuit could get a little simpler. Moreover, I'd suggest you a easy way to wire the shift-registers, without messing in a spaghetti-PCB. For just one sample (if does apply) isn't worthwhile. Consider four DIP-16 socket, for the four shift-regs. Now, take a socket and fold its leads of 90' outward, so that the socket looks "flatten". Then, consider each socket as it was as "floor" of a condo: since most of the 74HC595 leads are in parallel, you may wire easily the four sockets without getting crazy with a PCB. I hope you mean the trick... Cheers

[Bertrand Le Roy]

I really recommend using a LED driver such as this one: http://nwazet.com/leddriver (disclaimer: that's my shop; but you can find the equivalent Maxim chip pretty much anywhere). Less than $9 and able to drive a 8x8 matrix. It's the right tool for the job. I have a post on my blog showing how to control an 8x8 matrix with a single shift register: http://weblogs.asp.n...a-netduino.aspx but doing it with a LED driver is a lot cleaner: http://weblogs.asp.n...-right-way.aspx We have a library for the Netduino to drive the chip and a matrix behind it: http://netduinohelpers.codeplex.com/ By the way, this LED driver is what we use to drive the screen of our little game console kit: http://www.pix6t4.com I hope this helps.

[Mario Vernari]

I agree with you, Bertrand. If the leds are bright enough to get a good shining even with few milliAmps, a chip is surely the best solution. The problem could arise when you need many tens (or hundreds) of mA for each led (e.g. med/hi-power leds). As described I used very old leds, giving a poor brightness even with 10-20 mA. In such a context, the chip can't solve the problem, and it must be some kind of current driver. Again, I won't use such a '595 array for any commercial project, but for a home tutorial it explains a lot better how the things work. Cheers