+ Post New Thread
Page 4 of 4 FirstFirst ... 2 3 4
Results 61 to 73 of 73
  1. #61
    Advanced Member level 1
    Points: 2,189, Level: 10
    baileychic's Avatar
    Join Date
    Aug 2017
    Posts
    422
    Helped
    42 / 42
    Points
    2,189
    Level
    10

    Re: Embedded project needs devices which can work continuously at +125 degree C

    Regarding post #60 do I need an external Crystal at T1OSO/OSI pins so that I can make PIC wakeup from sleep using Timer1 ? By enabling T1OSCEN_bit ?



  2. #62
    Advanced Member level 1
    Points: 2,189, Level: 10
    baileychic's Avatar
    Join Date
    Aug 2017
    Posts
    422
    Helped
    42 / 42
    Points
    2,189
    Level
    10

    Re: Embedded project needs devices which can work continuously at +125 degree C

    We used Idle mode instead of sleep mode.

    I have a new question. Find the attached latest schematic (TMS-MB-SSL4.PDF). We had to revert back to MAX31855 and MUXs as PCB manufacturer was not able to pick and place 3mm X 3mm MAX31850KATB+ and also solder it.

    For our new design I want to know whether I have to put individual pull-ups on

    1. MAX31855 SCK line
    2. MAX31855 SO (SOx) line
    3. MAX31855 CS (CSx) line
    4. MUX1 SO line
    5. MUX2 CS line

    Edit:

    Refer TMS-MB-SSL5.PDF

    I have added pull-ups on SCK, SO and CS lines. Are these enough ?



    •   AltAdvertisment

        
       

  3. #63
    Super Moderator
    Points: 76,741, Level: 67
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    12,552
    Helped
    4185 / 4185
    Points
    76,741
    Level
    67

    Re: Embedded project needs devices which can work continuously at +125 degree C

    You only need one pull-up on each shared line. I'm not sure why you use the 74HC151 like that, to me it would make more sense to use a 3 to 8 decoder (74HC138 for example) and use it to select one of the eight thermocouple amplifiers at a time. Maybe there is more to the circuit than shown but it appears you are driving the CS signal 'backwards' to me.

    Do you really need to put the PIC to sleep between 'wake up calls'? In low power mode you can leave it running and still only draw a few uA of supply current. I would suggest you put as much of the remaining circuitry to sleep if possible but leave the PIC running on its internal oscillator. If you create the required delay in an interrupt driven timing routine you can power everything up, do the work and shut down again to save power. On most PICs you can software configure the internal clock divider so you can run it at low speed to do the timing delay then switch to full speed to do the work.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.


    1 members found this post helpful.

  4. #64
    Advanced Member level 1
    Points: 2,189, Level: 10
    baileychic's Avatar
    Join Date
    Aug 2017
    Posts
    422
    Helped
    42 / 42
    Points
    2,189
    Level
    10

    Re: Embedded project needs devices which can work continuously at +125 degree C

    Can you show how I can use 74HC138 to select one TC amplifier at a time ? I am not getting it. SCK line is common to all but CS and SO pins are different. Are you telling that I can connect SCK and SO lines of the TC amplifiers to 2 pins of PIC and just select the 74HC138 to select only the CS lines of 8 TC amplifiers ?



  5. #65
    Super Moderator
    Points: 251,556, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    43,810
    Helped
    13322 / 13322
    Points
    251,556
    Level
    100

    Re: Embedded project needs devices which can work continuously at +125 degree C

    Are you telling that I can connect SCK and SO lines of the TC amplifiers to 2 pins of PIC and just select the 74HC138 to select only the CS lines of 8 TC amplifiers?
    That's how SPI bus works. Review the interface description in datasheet, SO has internal tri-state driver enabled by CS.



  6. #66
    Advanced Member level 1
    Points: 2,189, Level: 10
    baileychic's Avatar
    Join Date
    Aug 2017
    Posts
    422
    Helped
    42 / 42
    Points
    2,189
    Level
    10

    Re: Embedded project needs devices which can work continuously at +125 degree C

    @FvM

    But where does the 8x CSx lines output come out of 74HC138 ? Which pin of 74HC138 I have to connect to PIC to control CS lines ?

    Is this correct ? Check the attached circuit and reply.
    Last edited by baileychic; 19th February 2019 at 15:56.



  7. #67
    Super Moderator
    Points: 76,741, Level: 67
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    12,552
    Helped
    4185 / 4185
    Points
    76,741
    Level
    67

    Re: Embedded project needs devices which can work continuously at +125 degree C

    The MAXIM data sheet explains the interface, it is basically SPI with no data input pin as the device is read only.

    The SCK is always an input to the device and you can share the same signal across many of them.

    The CS pin is an input to the device, it enables the SO pin which otherwise is tri-stated. This all the SO pins can share one connection.

    The SO pin carries 14 or 32 bits of data, clocked by the SCK signal. D0 is first and follows the first SCK after the IC is selected.

    So you can join all the SCK pins together and join all the SO pins together but you still need to drive a CS signal to each device. If your PIC software ignores anything on the pin SO is connected to, you can leave one of the CS signals active all the time, this means all you have to do is send the binary bits to select one of the MAX devices then send SCK pulses and at the same time read back the SO signal. You do need to be careful with the timing but that is a software issue, you just have to make sure SCK doesn't change between selecting a device and starting to read it.

    When CS is high at any of the MAXIM devices, it disconnects its SO pin so as long as only one device has CS low at a time, they will not interfere with each other.

    On your schematic it appears you are trying to use a 74HC151 to route the CS from the PIC to one of the devices, it will not work simply because the '151 works the other way around, it has 8 inputs and one output. The 74HC138 is a one-of-eight decoder, you give it a three bit selection code and one of the eight outputs goes low, the others go high. That is exactly what you need to select the MAXIM devices. You can leave the HC138's own enables permanently active.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.


    1 members found this post helpful.

  8. #68
    Advanced Member level 1
    Points: 2,189, Level: 10
    baileychic's Avatar
    Join Date
    Aug 2017
    Posts
    422
    Helped
    42 / 42
    Points
    2,189
    Level
    10

    Re: Embedded project needs devices which can work continuously at +125 degree C

    @ betwixt and FvM

    Got it.

    And I need 8x pullup resistors on the 8x CSx lines when 74HC138 is used ?



  9. #69
    Super Moderator
    Points: 69,598, Level: 64
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster 3rd Helpful Member

    Join Date
    Apr 2014
    Posts
    14,225
    Helped
    3250 / 3250
    Points
    69,598
    Level
    64

    Re: Embedded project needs devices which can work continuously at +125 degree C

    Hi,

    And I need 8x pullup resistors on the 8x CSx lines when 74HC138 is used ?
    No, because the HC138 outputs are push/pull and never high-Z.

    Klaus
    Please donīt contact me via PM, because there is no time to respond to them. No friend requests. Thank you.


    1 members found this post helpful.

  10. #70
    Advanced Member level 1
    Points: 2,189, Level: 10
    baileychic's Avatar
    Join Date
    Aug 2017
    Posts
    422
    Helped
    42 / 42
    Points
    2,189
    Level
    10

    Re: Embedded project needs devices which can work continuously at +125 degree C

    Any problem if I put pullup resistors on 8x CSx lines when 74HC138 is used ?



  11. #71
    Super Moderator
    Points: 69,598, Level: 64
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster 3rd Helpful Member

    Join Date
    Apr 2014
    Posts
    14,225
    Helped
    3250 / 3250
    Points
    69,598
    Level
    64

    Re: Embedded project needs devices which can work continuously at +125 degree C

    Hi,

    Any problem if I put pullup resistors on 8x CSx lines when 74HC138 is used ?
    No problem. Itīs just useless.

    Klaus
    Please donīt contact me via PM, because there is no time to respond to them. No friend requests. Thank you.


    1 members found this post helpful.

    •   AltAdvertisment

        
       

  12. #72
    Advanced Member level 1
    Points: 2,189, Level: 10
    baileychic's Avatar
    Join Date
    Aug 2017
    Posts
    422
    Helped
    42 / 42
    Points
    2,189
    Level
    10

    Re: Embedded project needs devices which can work continuously at +125 degree C

    Please check circuit in page no. 13/22. In the power supply filter circuits for C7 and C8 it is mentioned (NC) Not connected. Can I omit them from my circuit ?



  13. #73
    Super Moderator
    Points: 76,741, Level: 67
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    12,552
    Helped
    4185 / 4185
    Points
    76,741
    Level
    67

    Re: Embedded project needs devices which can work continuously at +125 degree C

    They are optional but I would fit them if possible. They should be as close to the Wroom as possible and be SMD or short wire through hole parts. They are there because the current drawn by the module can vary from just a few mA to 500mA very quickly as it transmits bursts of data, they help to prevent the supply dipping as the current increases because of impedances in the supply wiring. In essence, they work like small rechargeable batteries right at the place the power is needed so they can maintain the voltage under sudden load increases.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.


    1 members found this post helpful.

--[[ ]]--