Sorting Resistors with 3D Printing and a PIC

If you aren’t old enough to remember programming FORTRAN on punched cards, you might be surprised that while a standard card had 80 characters, FORTRAN programs only used 72 characters per card. The reason for this was simple: keypunches could automatically put a sequence number in the last 8 characters. Why do you care? If you drop your box of cards walking across the quad, you can use a machine to sort on those last 8 characters and put the deck back in the right order.

These days, that’s not a real problem. However, we have spilled one of those little parts boxes — you know the ones with the little trays. We aren’t likely to separate out the resistors again. Instead, we’ll just treasure hunt for the value we want when we need one.

[Brian Gross], [Nathan Lambert], and [Alex Parkhurst] are a bit more industrious. For their final project in [Bruce Land’s] class at Cornell, they built a 3D-printed resistor sorting machine. A PIC processor feeds a resistor from a hopper, measures it, and places it in the correct bin, based on its value. Who doesn’t want that? You can see a video demonstration, below.

At first, it appears the device uses a rotary encoder as an input device. However, it isn’t an encoder. It is a 10-turn potentiometer. This is simple to read but causes some unique processing. For navigating the LCD, for example, the PIC looks at the rate of change of the pot value. However, if it sees the pot go to the end of travel, it moves the navigation fully in that direction.

We thought it would be cool to marry this with an OpenCV resistor reader to also identify out of spec or mismarked resistors. There’s actually a few phone apps that can do that with varying degrees of success.

Thanks to [Bruce] for the tip, and for launching so many young engineers.

Filed under: 3d Printer hacks, Microcontrollers, tool hacks