Pullup in HC05 with atmega

Log in or register to post comments
Go To Last Post
7 posts / 0 new
Author
Message
SufyanRaza26
SufyanRaza26's picture
Level: Wannabe
Joined: Mon. Apr 8, 2019
Posts: 61 View posts
#1
Posted by SufyanRaza26: Wed. May 8, 2019 - 04:46 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi, i am using atmega128 with Bluetooth module HC05. I was having No trouble at all with the communication but reccently a new batch of bluetooth module arrived and with the same configuration when i replaced the new BT with the previous one, it doesn't recieve data properly. I found out the problem and placed a pullup resistor on my microcontroller RX and and Vcc and it sort of worked... My question is that does the BT module have a built in pullup resistor because previously it was working without Pullup resistor but the batch that recently arrive not a single one of them work without pullup resistor. and is there a way to check the presense of pullup resistor in bluetooth module HC05 .

Thanks 

Tags:

AVR Microcontrollers, megaAVR and tinyAVR
Last Edited: Wed. May 8, 2019 - 04:47 AM
Top
kabasan
kabasan's picture
Level: Resident
Joined: Mon. May 22, 2017
Posts: 749 View posts
Location: Japan
Posted by kabasan: Wed. May 8, 2019 - 04:59 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The interface of HC05 is 3.3V level.
Such things can happen if the atmega128 side does not follow it.
If you are using at 5V, you have to insert a level conversion.

Top
avrcandies
avrcandies's picture
Level: Raving Lunatic
Joined: Wed. Jun 30, 2004
Posts: 5612 View posts
Location: Cincinnati Oh
Posted by avrcandies: Wed. May 8, 2019 - 05:12 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

My question is that does the BT module have a built in pullup resisto

Not likely...since HC05 contains a logic gate output (TX) it will will drive hi/lo like any typical logic gate output (excepting things like open collector or open drain style gates).

It's possible they might have some resistors to define the levels during HC05 power off or reset, but not likely--they want to sell as cheaply as possible.

 

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Top
kabasan
kabasan's picture
Level: Resident
Joined: Mon. May 22, 2017
Posts: 749 View posts
Location: Japan
Posted by kabasan: Wed. May 8, 2019 - 06:25 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Do not sell something that is not designed correctly.
It will be a very annoying product.

Top
SufyanRaza26
SufyanRaza26's picture
Level: Wannabe
Joined: Mon. Apr 8, 2019
Posts: 61 View posts
Posted by SufyanRaza26: Wed. May 8, 2019 - 07:58 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

avrcandies wrote:
like any typical logic gate output (excepting things like open collector or open drain style gates).

 

I connected only VCC and GND and checked if there was some internal connection to TX but there was no volatage on TX of HC05 , which confirms what you said , However i am curious how it worked flawlessly when i had no Pullup resistor for one BT module and didn't work for a whole different batch when they both have no sign of internal pullups.

Last Edited: Wed. May 8, 2019 - 08:00 AM
Top
jgmdesign
jgmdesign's picture
Level: Moderator
Joined: Mon. Mar 19, 2007
Posts: 17426 View posts
Location: Long Island New York
Posted by jgmdesign: Wed. May 8, 2019 - 11:10 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

kabasan wrote:

Do not sell something that is not designed correctly.
It will be a very annoying product.


Tell that to Microsoft.........

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

Top
DocJC
DocJC's picture
Level: 10k+ Postman
Joined: Tue. Dec 11, 2007
Posts: 13109 View posts
Location: Cleveland, OH
Posted by DocJC: Wed. May 8, 2019 - 11:48 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Post a complete, and accurate, schematic diagram of your project.

 

JC

Top