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Logic Level Shifters for GPIO

muthukmk

Hi,

 

I have accumulated drivers and sensors for Arduino over a period of time. IR proximity, ultrasonic sensor , 4-channel relay module, handful of L293N motor driver modules, A4988 stepper sticks and corresponding CNC shield etc.

 

I have been successful in using them with Arduino (Mega and UNO). I have taken enough care in using those items which are power-hungry to be supplied with separate power sources and that approach worked well in Arduino context (eg. always power motors separately). Now, I want to use above sensors and actuators with Raspberry Pi 3 model B which I recently purchased. Now I need to find a proper way of dealing with logic-level related issues when I connect to RPi GPIO.

 

I have some doubts after going through experiences on Google on various Instructables / DIY projects if its good to use level shifters particularly while interfacing above components with RPi GPIO.

Many articles/discussions what I have read on internet seem to indicate that it should be ok to use them directly with RPi GPIO. But I wanted to confirm with those who would had been in similar situation. There may be more costly options (eg. a common adapter which lets such interfacing seamlessly possible without additional components )  which I want to avoid.

 

So, specific questions

a) Is it imperative to use logic level shifters to deal with 3.3v and 5v differences always for input as well as output ?

b) Or its more of experimenting and finding what works best for each of standard modules like relay / motor drivers / ultrasonic sensors / PIR sensors etc?

 

If I have missed any specific points to be added to the question, please let me know so that I can add the same

 

Regards

 

Muthu

  • in reply to johnbeetem

    You are right, I corrected my previous reply. But who knows, maybe there will be one in the future.

    BTW Cypress promised this "USB stick" like kit for the upcoming PSoC6, but this will take a while. The "big" kit is supposed to be available by the end of September and the smaller has only been confirmed as planned.

  • in reply to koudelad

    I'm using strategy 1 and 3 of this blog post.

     

     

    5V to 3.3V Logic Level Shifting Stragety Notes | James Reuben Knowles

     

     

    #1 works well if you need to drop a few data lines.

    For #3, you *have* to order the right IC because not all manufacturers have a chip with this desired (side) effect of being a level shifter.

    The chip I use (and also Gadgetfactory, who use it as a I/0 buffer for their Papillio boards) is the SN74CBT16245DGGR .

     

    I've done a few videos on the subject:

     

     

     

  • in reply to johnbeetem

    True. I'm a fan of the Cypress PSoC family.

    At the same time I also throw my hands in the air when someone (hey, Don) promotes them as logic level shifter, replacement for all FPGA or replacement for all ARM controllers.

     

    I like them, but they are just what they are: ARM microcontrollers with a little FPGA and analog configurable fabric. No magic. Just that.

  • in reply to Jan Cumps

    Hi Jan,

     

    I agree, for a simple level shifter, the PSOC is maximum overkill.

     

    I am just trying to promote the device to people and make them aware that it is a truly versatile little board that can be paired with an RPi or other computer to handle many I/O issues with just a bit of wiring and software.

     

    As for FPGA, now there you have misunderstood.  A complex project that requires fast response and a lot of logic will always need a FPGA.

    The PSOC can help provide many simple digital and analog blocks with FPGA like capability, but there are just too few of them on each board to consider using them for a complex project. image

     

    Magic is in the eyes of the viewer.  It may not be magic, but at times, it certainly looks close enough. image

     

    DAB

  • in reply to DAB

    Could you, please, share the schematics or principles how to do the level shifting? I would love to be the outcome of this dicussion, so even beginners (including me) will be able to perform this task using a PSoC.

  • the Sparkfun Level converter (https://www.sparkfun.com/products/12009) worked well for me ([Upcycle It] Nixie Display #9 - Hardware hacking ).

    There are other suppliers using the bss138 as well, Adafruit, ...