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