[time-nuts] Re: electronics question or how not to fry my raspberry pi

[Andrew Kalman]

 I find that the best way to handle these translations is to use one of
TI's level translators ... each chip has two power supply rails, and
translation is done transparently across the chip, and there is good max
voltage overprotection on both sides  as well. I use them a lot to handle
5V <-> 3.3V level issues.

Try the SN74LVC8T245PWR for unidirectional level translating . They also
have some bidirectional ones ...

--Andrew

--------------------------------
Andrew E. Kalman, Ph.D.


On Fri, Jan 28, 2022 at 11:41 AM folkert <folkert at vanheusden.com> wrote:

> Hi,
>
> I bought a GPSDO. It outputs somewhere around 3V. This is connected to a
> picdiv and then to a raspberry pi. The picdiv is happy with 3.3v, the rpi
> as well. All good.
>
> Now I bought a "Square Wave Amplifier" by BG7TBL (
> https://www.aliexpress.com/item/4000192799858.html?gatewayAdapt=glo2nld&spm=a2g0o.9042311.0.0.3d764c4dMZPAX8
> ). Documentation I could find was a bit vague about the
> output voltage but I measured 5v with a scope (see
> https://vanheusden.com/permshare/scope.png - the scope software says
> 2MHz but output is really 10MHz).
>
> I did not study electronics, am only a electronics-hobbyist so bare with
> me when this is a dumb question.
>
> The RPI doesn't like 5v on its GPIO pins.
> So I wonder:
> - can I feed the picdiv 5v on its GPIO pin while giving it a 3.3v
>   voltage so that it outputs 3.3v as well to the rpi pins?
> - or should I use a voltage divider? I was thinking of a 4.7k ohm and
>   8.2k ohm resistor giving slightly less than 3.2v - will that work? or
>   will that attenuate the signal too much? The 50 ohm bnc cable between
>   the amplifier and the rpi is 3m long. Anything else I should be aware
>   of?
>
>
> Regards,
>
> Folkert van Heusden
> PD9FVH
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