Series resistor value problem

Log in or register to post comments
Go To Last Post
6 posts / 0 new
Author
Message
Keith Salazar
Keith Salazar's picture
Level: New Member
Joined: Fri. Jun 14, 2019
Posts: 2 View posts
#1
Posted by Keith Salazar: Fri. Jun 14, 2019 - 08:44 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

 

I'm having problems with my transceiver because of the R167-(10k ohms) resistor.

The voltage of DIR_CON is low. (I need it to be low for the transceiver to act receiver)

But measuring the voltage after the resistor it was 1.4V

Because of this the transceiver is acting like a transmitter.

Changing the value of the R167 to 3k ohms, it worked fine.

 

My question is why did the resistor had that effect to the voltage of DIR_CON?

THANK YOUUU!!!

 

This topic has a solution.

keiithyyy

Tags:

Learning and Information, General Electronics, solved
Last Edited: Mon. Jun 17, 2019 - 12:18 AM
Top
Kartman
Kartman's picture
Level: 10k+ Postman
Joined: Thu. Dec 30, 2004
Posts: 22148 View posts
Location: Melbourne,Australia
Posted by Kartman: Fri. Jun 14, 2019 - 09:01 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The question is why you had the resistor wired that way in the first place! The resistor should be between GND and re/de to ensure the transceiver defaults to receive when the micro is in reset.

Top
Brian Fairchild
Brian Fairchild's picture
Level: Raving Lunatic
Joined: Thu. Oct 18, 2001
Posts: 4185 View posts
Location: Eastern England.
Posted by Brian Fairchild: Fri. Jun 14, 2019 - 09:03 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The input current into DE and /RE are spec'd at a maximum of 50uA. 2 x 50uA x 10k = 1V. Add on the output low voltage of your driving chip and you have your answer.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

Top
m.majid
m.majid's picture
Level: Hangaround
Joined: Fri. Dec 5, 2008
Posts: 157 View posts
Location: Türkiye
This reply has been marked as the solution. 
Posted by m.majid: Fri. Jun 14, 2019 - 09:27 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 1

see the datasheet of SN75LBC184

your circuit is quite different from what recommended in datasheet.

see 11.1 Layout Guidelines , there is also a pull-up res at PIN 1(R)

Majid

Top
Keith Salazar
Keith Salazar's picture
Level: New Member
Joined: Fri. Jun 14, 2019
Posts: 2 View posts
Posted by Keith Salazar: Mon. Jun 17, 2019 - 12:21 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thank you for the answers!

I didn't design the ckt btw. I just re-used it.

But its my fault not reading more of the datasheet.

keiithyyy

Top
avrcandies
avrcandies's picture
Level: Raving Lunatic
Joined: Wed. Jun 30, 2004
Posts: 2978 View posts
Location: Cincinnati Oh
Posted by avrcandies: Mon. Jun 17, 2019 - 12:45 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I didn't design the ckt btw. I just re-used it.

Now you can tell them you have a secret way to improve their intermittent problems that they didn't want to tell you about. 

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

Top