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

[Robert Atkinson]

 You can run the PicDiv on 3.3 V and connect the 5V signal to the PicDiv input via a series resistor between 1k and 10k. Put the resistor at the PicDiv end of the connection. 
The PIC has protection diodes on it's input These clamp the input to the supply. The series resisor limits the current. This is robust. There are thousands of devices out there with a pin conneted to the mains with just a series resistor. t's used for zerocrossing detection or monitoring the mains frequency.
Robert G8RPI.

    On Friday, 28 January 2022, 20:06:20 GMT, 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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