Finite State Machine Panel Assembly

A project log for TMD-1: A Turing Machine Demonstrator

Develop a Turing machine that is simple to program and easy to understand.

Michael GardiMichael Gardi 08/14/2020 at 14:190 Comments

Like the Tape Panel the Finite State Machine Panel was printed in two parts.

Here I also printed some braces and used some gel superglue along the edges and to attach the braces.

Preparing The Transition Table Reader

The PCB I designed for this arrived this week.

I have to admit this is version 2. The first board was too big. I had failed to allow enough clearance for the lamps and switches that will surround it. Also I found that the .05 pitch spacing for the TO-92 leads was a bit too challenging for my soldering skills, so I spread the leads out to .1 pitch in this version. Live and learn I guess. Costly lesson though.

First I installed the headers that will bring out the signals for the 33 Hall Effect sensors. These are mounted on the back of the board.  Once soldered, trim the short leads on the front of the board as close as possible to the PCB.

Next I started installing the sensors. There are a couple of things I had to be careful of here. Since I wanted the sensor to lie flat on the PCB I needed to make a 90 degree bend in the leads.  It was also important to do this consistently for all sensors so I made a little jig.

The idea is to lay the sensor into the slot as far up as it will go.

And here is the second important thing. The sensor must be "face up". That is to say the face with the two facets visible on the left and right and the lettering must be visible. Holding the sensor firmly in place, bend the leads back 90 degrees.

The outer leads can then be spread out slightly from the center lead, inserted into the front of the  board, and soldered in place.

Repeat 32 more times.

Mounting the Transition Table Reader

The Transition Table Reader is mounted on the back of the Finite State Machine Panel. The Hall Effect sensors must be carefully aligned with the shallow indentations where the tiles will be placed so that they can get a good read on the embedded magnets.

I found that the easiest way to do this was to hold the Transition Table Reader board roughly in place behind the Finite State Machine Panel while shining a bright light through the PCB from behind. You will be able to see the "black dots" of the sensors through the thin floor of the tile cutout areas. For the top two rows the single "dot" should be in dead the center of the tile cutout areas. 

The last row has two dots for each cutout that should be diagonally arranged at equal distances from their corresponding corners in the cutout area. 

When everything is lined up tape the PCB in place. (NOTE: This process is much easier if two people are involved.)

I printed some brackets to hold the Transition Table Reader board in place.

Carefully go around the PCB replacing the tape with the brackets that get glued to the back of the Finite State Machine Panel.

Almost done in this photo.

Add the Switches and Lamps

Install the lamps and switches as shown in the next two photos.

One final sensor alignment check.  Looking good!

And now that's the Finite State Machine Panel ready to be wired into the rest of the project.