[sudo-discuss] vending machine homing switch mystery solved

[Jake]

mitch there are 42 motors, arranged in a row/column grid

this way there are no extra wires.  you have to be able to detect the 
"home" state of each product independantly!

the other vending machine, a "snackshop II" uses a totally different 
system.  AC power is wired to all the motors through their homing switch, 
so they will automatically turn until they are at "home" position.

Then there is a single wire from each motor to the appropriate button on 
the front of the vending machine, and when the meatbag presses the button 
of the product they want, current flows through the money-counting circuit 
(and through diodes corresponding to the 5-bit value of nickels to charge 
for the product!) and if the mortal has paid for its food, the circuit is 
closed and the motor runs despite its Home position - but only for long 
enough for the motor to leave "home" and then the home switch runs the 
motor until it gets home again - after the user has been served.

we use this charlieplexed optocoupled-triac board for that machine:

https://github.com/sudoroom/hackomat

-jake

On Sat, 9 Apr 2016, Mitch Altman wrote:

> That is a bizarre way of detecting "home".  Since there's a switch, wouldn't it be easier to just connect the switch directly to the Arduino to detect "home"?
> 
> 
> -----------------
> > Date: Sat, 9 Apr 2016 17:42:06 -0500
> > From: jake at spaz.org
> > To: sudo-discuss at lists.sudoroom.org; adam at aperture.systems; organic_unity at yahoo.com; emmaselephants33 at gmail.com; echoudhry at gmail.com
> > Subject: [sudo-discuss] vending machine homing switch mystery solved
> >
> > so i've been working on the black sudoroom vending machine (vending1):
> >
> > https://sudoroom.org/wiki/hack-o-mat
> >
> > which had previously been hacked by students at UC Berkeley (i think)
> >
> > I believe it's a Snacktron like Emma and Ed's machine.
> > (unlike our brown vending machine which is a snackshop II)
> > pictures of their machine can be seen here:
> > http://spaz.org/~jake/pix/vend/
> >
> > they had ripped out the original control unit, and wired it up with a
> > bunch of reed relays and an arduino. The motors of the vending machine
> > are wired as a grid of rows and columns, so the controller needs to be
> > able to enable a single row and column in order to power one product
> > motor.
> >
> > But it also needs to be able to detect when the product motor has rotated
> > a full turn, and is back at the "home" position where it needs to stop.
> > There's a "home" sensor on the back of the motor, but the way it's wired
> > was a mystery for a while. Here's some pictures of the homing circuit:
> >
> > http://spaz.org/~jake/pix/vend/IMG_20160401_015211.jpg
> > http://spaz.org/~jake/pix/vend/IMG_20160401_015700.jpg
> >
> > as you can see, the only difference between the button being pressed or
> > not pressed, is that the 420nF capacitor is in parallel with the motor or
> > not. Since the whole thing is in series with a diode (to protect against
> > trying to turn a motor backwards) we were stumped as to how to detect
> > whether a motor was homed or not.
> >
> > Thanks to Zach who donated some test equipment including this awesome
> > signal generator (along with a nice power supply and bench multimeter):
> > http://imgur.com/LTSFfOe
> >
> > I was able to connect an AC waveform in series with a 12VDC supply to one
> > of the motors, and figure out how to detect whether the home switch is
> > closed or not. Basically, you make a 31KHz (or similar frequency)
> > squarewave in series with the power supply, and watch the current through
> > the motor. If the button is open and the capacitor is not in-circuit, the
> > motor's inductance absorbs the AC and the current draw is relatively
> > smooth. But when the motor arrives at the home position (when you need to
> > stop delivering product!) the capacitor gets switched in, and now you'll
> > see a lot of the AC on the current path of the system.
> >
> > Here is a video showing the voltage across a 22-ohm series resistor while
> > the motor is rotating with 12VDC:
> >
> > https://www.youtube.com/watch?v=xHIGDw5HRCg
> >
> > apparently it takes that motor about 11 seconds to dispense a product and
> > finish returning to home position, assuming the product weighs nothing.
> >
> > by the way, you'll notice that i'm using the old analog oscilloscope.
> > Unfortunately the LeCroy 9510 has started crashing, basically
> > bluescreening. It probably needs to be opened up and cleaned, as it got
> > wet after a fire before it was donated to sudoroom.
> >
> > Or maybe someone wants to donate a nicer oscilloscope to sudoroom?
> >
> > anyway, now I know how to detect the motor homing signal, and I just need
> > to wire up this machine to its arduino to detect the signal and dispense
> > product more accurately. If anyone wants to help, please let me know.
> >
> > by the way, if you are wondering how the UC students detected when the
> > motors were finished dispensing product, the answer is absurd:
> >
> > they put a laser beam across the path where product would fall when
> > dispensed, and they watched for the laser beam to be interrupted.
> >
> > did it work? I don't know. probably the semester ended and they got
> > their grade and moved on, and then they donated the vending machine to us.
> >
> > -jake
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> > sudo-discuss at lists.sudoroom.org
> > https://sudoroom.org/lists/listinfo/sudo-discuss
> 
>