Review My Schematic PLEASE.

Hello everybody,

I'm going to start by saying that I consider myself an EXTREME novice in the world of electronics and programming, but I really want to learn this awesome stuff. Anyway, I recently finished building my Mendel90 3D printer and decided I wanted to make something like http://www.thingiverse.com/thing:13099.

Ultimately I want to print a few more of these and create a clock or calendar. I went ahead and made some small tweaks to the original design by making it slightly thicker, a little taller, and removed the dot. Here is the back my 7 segment display printed with LED's in place for demonstration purposes.

In my efforts to teach myself and learn more about electronics I really wanted to design the schematic myself. I feel the best way to learn is to actually do it yourself. I also decided with this project that I wanted to learn about multiplexing and shift registers, but I didn't just want to breadboard something and then tear it all apart. I drew this thing up using an ATTINY85. To be honest I hope an ATTINY will even work in this setup. That's why I'm here, I really want to see if my schematic is completely wrong or if I'm getting close. From what I've read I'm thinking that the LED portion of the schematic needs to be changed, maybe not. :~ I say that because I'm going to be using white LED's. I don't have a datasheet for them so I'm assuming 3.3Vf and 20mA. Maybe I don't need to change anything with the LED's at all, my complete "newbieness" is becoming more apparent.

Here are the areas that I'm still questioning.

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Tom… :slight_smile:

Is that a good stable and regulated 12V ? So you can use it for the leds ? Is that schematic for a single digit ? Are the three leds of a segment always turned on together ? Why do you use transistor for the seperate groups of leds ? The 74HC595N can not supply 60mA. If all the transistors are switched on, there are three leds parallel with just one resistor. It will work, but perhaps a few leds will be dim.

You can use any pins of the ATtiny. As long as the MOSI, MISO, SCK can be controlled by a programmer.

But why an ATtiny ? Using an Arduino board will be easier in the end.

Way too complicated. Just use a single TPIC6B595 to sink current thru all 3 LEDs in series for each segment.

This board combines Arduino functionality with up to 12 shift registers for sinking current thru high voltage displays like that.
http://www.crossroadsfencing.com/BobuinoRev17/

OE/ can be connected to a PWM as well for brightness control.

I appreciate the responses. Crossroads, I didn't even know such a chip existed. I guess that just shows how much of a rookie I really am. If I read this right, you're saying that I can just eliminate all of my schematic with the 74hc595 and the LED's onward and replace it with TPIC6B595 schematic that you have drawn up. This assumes that I provide proper voltage, etc.? Seriously, thanks a million.

Yes. I learned about this chip from another forum member a couple of years ago. It's a nice one to use with Arduino's.