[Dprglist] 5v sensor to 3.3v GPIO interface?

[Karim Virani]

These have worked well for the 5v quadrature encoders we use:
http://www.revrobotics.com/rev-31-1389/


On Thu, Jul 11, 2019 at 12:57 PM John Swindle via DPRGlist <
dprglist at lists.dprg.org> wrote:

> Clay,
>
> I assume when you say the resistors pull the output down a lot, that you
> mean it is pulled below 3.3 volts. If so, it seems the high resistor is too
> large or the low resistor too small. If the calculated ratio seemed good,
> remember that 10% tolerance resistors are NEVER the marked value, having
> been binned.
>
> Conventional PCI used open drain, sustained tristate. When low value
> pullups are used, the signals restore faster but burn more power. If speed
> is not a concern  use large value resistors. The sensor's DC drive strength
> may not be able to overcome low values.
>
> Good luck with your team!
>
> John Swindle
>
>
> -----Original Message-----
> From: Clayton Timmons via DPRGlist <dprglist at lists.dprg.org>
> To: DPRGlist <DPRGlist at lists.dprg.org>
> Sent: Thu, Jul 11, 2019 10:31 AM
> Subject: [Dprglist] 5v sensor to 3.3v GPIO interface?
>
>
>
> I'm helping a solar car team with telemetry.   Using a Raspberry Pi with
> touchscreen on the car's dashboard to display data, log it, and push to the
> cloud.  Thanks for help from DPRGlist,  James LeRoy pointed me to
> io.adafruit.com which was very helpful.  We had the example up and
> running in just a few minutes.  We have a cellular WiFi hotspot with dual
> antennas on the car.
>
> We are in the last few days of work before the multi-day race event.   The
> last big crunch trying to get everything working.   We've added a rotation
> sensor on the drivetrain and hope to get distance and speed from it.
>
> There was one issue connecting the rotation sensor to the Raspberry Pi.
>  The rotation sensor is an open collector type device which pulls down to
> ground when the magnet is sensed.   The rotation sensor works from 4-12v.
>  We decided to run it off 5v which is available on the Raspberry Pi
> connector.
> The output of the rotation sensor is normally about 4.7v and the GPIO on
> the Raspberry Pi is 3.3v  not 5v tolerant.     I was hoping a simple
> resistor divider could do the trick to interface the sensor to the
> Raspberry Pi GPIO.   It seemed like the loading of the resistor divider was
> pulling down the sensor output quite a bit.
>
>
> Any recommendations for a really simple circuit to interface the 5v open
> collector sensor to the Raspberry Pi GPIO?
>
> Thanks,
>
> -Clay Timmons-
>
>
> _______________________________________________
> DPRGlist mailing list
> DPRGlist at lists.dprg.org
> http://lists.dprg.org/listinfo.cgi/dprglist-dprg.org
> _______________________________________________
> DPRGlist mailing list
> DPRGlist at lists.dprg.org
> http://lists.dprg.org/listinfo.cgi/dprglist-dprg.org
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.dprg.org/pipermail/dprglist-dprg.org/attachments/20190711/74c3259e/attachment-0001.html>