[sudo-discuss] Vending machine feedback

Marc Juul marc at juul.io
Thu Feb 22 22:18:32 PST 2018

The raspberry pi is not a real-time system, nor would the serial input
automatically trigger an interrupt on the raspberry pi and the raspi
digital input is unbuffered. Thus if the raspberry pi was too busy with all
its multitasking it might miss the input from the bill acceptor and money
would be accepted with nothing given in return. The arduino is there to
provide buffered input. Right now it's not really doing that properly since
it's just relaying immediately to the raspberry pi. What should happen is
that it should buffer the input, then tell the raspberry pi and wait for an
acknowledgement, buffering all input repeatedly telling the raspberry pi
until acknowledgements are received. This also protects against raspberry
pi crashes or crashes of the high level software running on it. Crashing
the compiled program on the Atmega microcontroller on the other hand is
much harder to do.

On Thu, Feb 22, 2018 at 3:25 PM, Thomas Levine <_ at thomaslevine.com> wrote:

> The vending machine now provides some more feedback after money is put in.
> Source code associated with my contribution is here. I haven't documented
> the other components of the vending machine.
> https://thomaslevine.com/scm/sudo-vending
> Based on the implementation details, it appears to me that
> the bill acceptor is in fact plugged into one board (Arduino Leonardo)
> that is connected by serial to another board (Raspberry Pi). Why is
> the former board used at all? That is, why is the bill acceptor not
> plugged directly into the latter board?
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