Re: Inverting RST pin (using configuration file) not working on Raspberry Pi?

[Martin Stejskal]

Hi, basically you need to cascade them. Output from 1st part will be routed to input of 2nd part. Like at old-school analog amplifiers.

Sorry, too tired today. Tomorrow I can send better schematic and description.

Regards

 Martin

On Tue, Jun 1, 2021, 22:01 John Klimek <jklimek@gmail.com> wrote:

Interesting ideas, thanks!

How would I connect a second transistor to re-invert the signal?
Also, could I use a PNP transistor instead?

I'll have to think a bit more about the second idea and see if I can
understand what you're saying.

On Tue, Jun 1, 2021 at 3:56 PM Martin Stejskal <martin.stej@gmail.com> wrote:
>
> Hi, instead of hacking SW, why not hack HW? Add one more extra NPN, so it will invert signal again?
>
> Depends how brave you are, but there is also another (bit more dangerous) way - add serial resistance. Thing is that every GPIO suppose to have some protection diode (in generic - "every" IC - there are exceptions of course). They typically stand like ~1 mA without problems. I assume that your reset pin on Arduino have 22k pull-up -> use serial resistance ~1/10 of that -> 2k2 -> ~70uA leakage when GPIO on Rpi will be 3.3V. That should not burn Rpi's GPIO. When GPIO on Rpi will be in low, current will be ~200uA, but it will be leaking through switch transistor, which actually can deal with much higher currents.
>
> But before you do any HW changes, make sure you made calculations (worst case) and all necessary measurements before trying on real HW. You have been warned.
>
> When you think about attached schematic, it is just 2 resistors with 2 different power supplies -> quite easy math. If you're not sure, any free simulator can help you out.
>
> Best regards
>   Martin S.
>
> On Tue, 1 Jun 2021 at 19:59, John Klimek <jklimek@gmail.com> wrote:
>>
>> I'm using avrdude (v6.3-20171130) on my Raspberry Pi, but I need the
>> RST pin to be inverted because I'm using an NPN transistor to protect
>> the RPi from my Arduino's 5V power.
>>
>> Here is the command line I'm using for testing:
>>
>> avrdude -C /root/hid/.platformio/packages/tool-avrdude/avrdude.conf -C
>> +avrdude-rpi.conf -P /dev/spidev0.0:/dev/gpiochip0 -c rpi -p m32u4 -v
>> -v -v -v
>>
>> Here is avrdude-rpi.conf:
>>
>> programmer
>>         id = "rpi";
>>         desc = "RPi SPI programmer";
>>         type = "linuxspi";
>>         reset = ~25;
>>         baudrate = 400000;
>> ;
>>
>> Here is the avrdude output:
>>
>> avrdude: Version 6.3-20171130
>>          Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
>>          Copyright (c) 2007-2014 Joerg Wunsch
>>
>>          System wide configuration file is
>> "/root/hid/.platformio/packages/tool-avrdude/avrdude.conf"
>>          User configuration file is "/root/.avrduderc"
>>          User configuration file does not exist or is not a regular
>> file, skipping
>>          Additional configuration file is "avrdude-rpi.conf"
>>
>>          Using Port                    : /dev/spidev0.0:/dev/gpiochip0
>>          Using Programmer              : rpi
>>
>> avrdude done.  Thank you.
>>
>> I've checked the RST pin (25) on my oscilloscope and it's not
>> triggering at all when I use the inverted (~) syntax.  If I remove the
>> (~) then it does trigger the RST pin but not inverted as I need.
>>