Making a POV led Globe

aliw · Post by **aliw** » Sun Jun 27, 2010 1:58 am

sorry that I wasn't on the web for a while but I was very busy with school projects and other stuff.
I wanted to ask you brad if you could check my schematic. Because this is my first one and I am not 100% sure everything is connected correctly.

I sill have a question, as I understand all IC's need +5V to operate right?

Post by **brad** » Sun Jun 27, 2010 9:16 pm

No problem buddy

Yes that is basically correct. Pretty much all IC's these days have adopted the TTL logic levels which is pretty much 5v.

There are tolerances but if you are unsure, just look up the datasheet for your particular part.

aliw · Post by **aliw** » Fri Jul 02, 2010 12:56 am

As I was looking trough some schematics I noticed that nearly every schematic has a `electricity filter` (I know it has something to do with noise and capacitors). My question about this: Why would you need to filter electricity? What is causing that noise? Do I need a filter on my project? How to make such a filter?

Chuckt · Post by **Chuckt** » Fri Jul 02, 2010 6:06 am

My dad said that capacitors are like shock absorbers on a car. It has a way of smoothing it out. A lot depends on how they are made.

I suppose you could filter with resistors just to find that a little bit of it is still there.

Post by **brad** » Fri Jul 02, 2010 6:20 am

Basically you have a filter capacitor connected between ground and vcc of each chip. What can happen internally is that you get multiple transistors turning on which effectively creates a short circuit from VCC to GND.

Since this is only for a split second, it kind of looks like an AC signal (high frequency), since the capacitor looks like a short circuit to high frequency, it shunts the current away from the chip, through to ground.

aliw · Post by **aliw** » Sat Jul 03, 2010 6:07 am

Ok, can you make a small schematic of this? This will help me alot. Just as an example. As I understand I don't have to use large ones. 0.1hF will be enough right?
As for the programming of my pic I was looking for the pickit on ebay but I've found out that there is a pickit3. (This one is a little more expensive) But is there a big difference between the pickit2 and the pickit3?
Links of what I've found.
http://cgi.ebay.com/Pickit2-Clone-/1604 ... 255aee506a

http://cgi.ebay.com/Clone-Microchip-Dev ... 1712078781

aliw · Post by **aliw** » Sat Jul 03, 2010 6:25 am

I have a question about the 74373 is there a big difference between the 74HC373 and the 74HC373N? I've got a look trough the datasheet but that didn't help me alot. (It only made me more confused).

http://cgi.ebay.com/50pcs-DIP-IC-74HC37 ... 4aa046eb19

Post by **bitfogav** » Sat Jul 03, 2010 6:31 am

aliw wrote:I have a question about the 74373 is there a big difference between the 74HC373 and the 74HC373N? I've got a look trough the datasheet but that didn't help me alot. (It only made me more confused).

http://cgi.ebay.com/50pcs-DIP-IC-74HC37 ... 4aa046eb19

It is in the datasheet, the difference between a 74373 and 74373N are the markings on the chip.. Thats all it is.

aliw · Post by **aliw** » Tue Jul 06, 2010 4:03 am

I think you guys have missed my question asked earlier. About the example of the filter and the difference between the pickit2 and pickit3. please reply on that.

Post by **bitfogav** » Tue Jul 06, 2010 6:08 am

aliw wrote:I think you guys have missed my question asked earlier. About the example of the filter and the difference between the pickit2 and pickit3. please reply on that.

Here is an example of a capacitor filter on a 16F648A, I would recommend using a 100nf capacitor as this would do the job on most projects, And as for the pickit 2 and pickit 3 in your links above, they are CLONES, Im not saying that they would not do the job but just pointing out that they are copies? I would recommend the pickit2 has most of the people I know use them and I have got one myself and they are so easy to use, and I think the difference between a pickit2 and pickit3 are the types of microchips they will programme?, the pickit2 covers most of them but I think the pickit3 will do them all?

Maybe Brad knows more about this?

Post by **brad** » Thu Jul 08, 2010 11:11 pm

Yep, couldnt have put it better myself!

The capacitor is there to shunt any AC or high frequency noise to ground. In high speed devices like a microcontroller, it is easy to generate unwanted noise. A capacitor is basically a short circuit to high frequencies (but open circuit to DC) so it will shunt through the cap instead of through the chip.

I would highly recommend getting the pickit 2. It really will do all you need it to and covers practically all pic micros.

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