Super Glue Gun 08: Integrating All Mechs -- Episode 310

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Previously, the team added the mechanism for the auto stand using a metal wire stand and a guitar string acting as a cable. The cable is actuated by a servo and utilizes a servo library for the Atmel ATTiny20 Microcontroller they are using.  Now they need to find a capacitive touch sensor library, possibly Qtouch from Atmel, to allow the auto stand to retract when your finger touches the trigger.

Ben goes to work on Autodesk Fusion 360 to design the parts he’ll need for 3D printing.  He filets the edges to form a round enclosure for the magnet and makes room for the capacitive touching piece.  After he’s printed the two piece he’s ready to build an autostand mock up.

He builds the mockup on top of an existing mock-up and puts it on the glue gun mech for testing before they do a redesign of the case. He flips the barrel around so that the hot block is at the top and gives them more room for their stand. He needs to use a spacer on it because the stand has an extremity that needs to be clear of the heater barrel. This requires hot gluing together the hot glue gun. When he’s done he got a proof of concept that he can use before they redesign the top half of the glue gun.

While Ben is working, Felix is researching the Qtouch library, a proprietary library for Atmel microcontrollers, for use with the touch sensor. Ben’s already printed out the holo trigger and put the magnet in place. The sensor will go on the front with the wire coming out the back.  They’ll glue it together and put in the spring.  After they know the magnets correct orientation they can proceed with placing metal along with wires and use it as the touch sensor.

As it turns out the Atmel Qtouch library supported almost every ATTINY except the one they selected.  Ben and Felix turn to github where they find a library they can possibly use called tiny touch. It’s got an entire Atmel solution file attached to it, as well as, schematics that they can use with their Atmel microcontroller. The user even uses some machine language to do the timing for the neopixels. This allows you to know exactly how many cycles are executed. The code they are looking at works much like the official Qtouch libraries, but with a smaller code footprint.

After modifying code, Ben puts the prototype back together, and looks for the max resolution on his ADCs so he can get a detailed temperature reading from the glue gun.  He’s got a pair of 100K resistors in parallel to cut the resistance down to 50K, the value they want. Ben performs a soldering trick, heating up the wire just enough to cause plastic to contract. He uses a Rohde & Schwarz oscilloscope to double check the signals are in harmony.  He puts the case together, and modifies the code so that instead of blinking an LED when you touch the trigger, it changes the servo to its two different states, to retract and extend the stand.

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