Go Down

Topic: Which Capacitor I needed (Read 2362 times) previous topic - next topic

allen727hk

Apr 03, 2017, 06:50 am Last Edit: Apr 04, 2017, 07:38 am by allen727hk
I am finishing a DIY item which contains:
  • 1 x ATtiny85
  • 1 x 74HC595
  • 7 x LED (Red color)
  • 7 x 300 Ω Ohm
  • 1 x CR2032 (Seems not working cause too low voltage, but actually I planned to use this)
  • 1 x Li-ion Rechargeable battery (280mA - 700mA, both work but the size too large, want a slim case)


The stuff is using ATtiny85 via 74HC595 to control 7 LEDs to blink. All the LEDs are ON often.

Question: Which Capacitor I needed, and where I put it into??

Detail information (Schematic, diagrams) can be share at here later.

* Sorry for my poor English.

ChrisTenone

Share your schematic now. You will need a couple 0.1uF capacitors (ceramic are best for this use) attached directly to the Vcc pin of both chips, and grounded on the other leg of the cap. Do a site search for "decoupling capacitor".
What, I need to say something else too?

MarkT

CR2032 cells are good for 1mA or maybe 2mA, that might be something you don't realise.

You need to decouple each logic IC with 100nF on each supply pin to ground, and maybe
22 to 47uF electrolytic somewhere on the supply for good measure.

How are you clocking the ATtiny?
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

allen727hk

Share your schematic now. You will need a couple 0.1uF capacitors (ceramic are best for this use) attached directly to the Vcc pin of both chips, and grounded on the other leg of the cap. Do a site search for "decoupling capacitor".
Sure, I will draw the schematic and upload to here asap, hopefully can be done in coming hours. :)

allen727hk

CR2032 cells are good for 1mA or maybe 2mA, that might be something you don't realise.

You need to decouple each logic IC with 100nF on each supply pin to ground, and maybe
22 to 47uF electrolytic somewhere on the supply for good measure.
Ooops, seems that is impossible to using CR2032.


How are you clocking the ATtiny?
Following this tutorial to clocking ATtiny, http://highlowtech.org/?p=1695

For this project, I am using internal 8MHz clock.

allen727hk

Hi all, attached the schematic to the post, thanks all.

ChrisTenone

Your battery symbol is drawn backward. The longer bar is positive:


         |
       + |
      -------
       -----
      -------
       -----
       - |
         |
What, I need to say something else too?

allen727hk

Your battery symbol is drawn backward. The longer bar is positive:
I am beginner, just thanks for your remind.

MarkT

And you have drawn 2 cells in series - wasn't this a single CR2032? 
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

allen727hk

I have three CR2032, but in this project I prefer use one only. After you mention there is only 2mA current output for each CR2032, I had Google, however, you are right. According to Wikipedia, the max pulse is ~15mA. Which is unable to make all LED on.

Therefore, I may use Li-ion rechargeable battery for this project, which is providing at least 3.7v, and I had a test, all LEDs both can blink.

But still want to know that, is it need a capacitor for this project?

MarkT

Hang on, are you wanting a storage capacitor for powering the LEDs for pulses?  You didn't say so.

Firstly you need 0.1uF decoupling caps on the logic chips as explained above.

Secondly for bolstering the supply for pulse operation you need to explain how much current for
how long you need - and how much voltage droop you can tolerate during the pulse.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

allen727hk

Actually, I am finishing this stuff:
https://instagram.com/p/BSSok3Rjwpu/

JohnRob

Please do not PM me with thread based messages.  If your thoughts are worth responding,  the group should benefit from your insight.

ChrisTenone

...
But still want to know that, is it need a capacitor for this project?
I told you the answer in reply #1. You were probably dazzled by my ASCII art! ;)
What, I need to say something else too?

Go Up