VK - LED Bar Graphs

A project log for Voight-Kampff Machine

Distinguishing Humans from Replicant's

Tom MeehanTom Meehan 04/24/2017 at 00:160 Comments

Light Bar Above Main Screen

For this bar graph I'm currently using 12 - 2x5mm rectangular LED's (I used Red/Green LED's that have 3 leads - common cathode, 2 anodes 1 for each color). I was thinking to make a more graded display (2 levels for each LED – green then red so 24 levels) but realized that wouldn't really match the display in movie. The movie display looks like a 8 Red then 4 Green array, so I'm only using 2 leads for each LED – 8 with Red anode and 4 with Green anode (final design will use single color LED's).

I'm currently using two SN74HC595 - 8 bit serial to parallel out shift registers to control the LED's. This means that 16 bits of information (0 or 1 / on or off) are sent out (4 bits are unused since there are only 12 LED's). A great tutorial on using these shift registers with LED's and Arduino's is at Adafuit - Arduino Lesson 4.

Light Bar Below Small Screens

The 10 bar LED below the 2 smaller screens, on the left side (from the examiners point of view).

These LED bar-graphs seem to fit, they are come in a 20 DIL package with a 2.54mm pin spacing (they fit perfectly on a solder-less breadboard, bridging the middle of the board). My initial idea was to use shift registers (74HC595's) for this bar-graph also but remembered a circuit I built following a tutorial a few years ago that used a single Johnson Decade Counter (CD4017BE) to control all 10 LED's and at that time I adapted it to work with an Attiny85 using an analog input (voltage divider made of a resistor and a 10K thermistor – for basic temperature biofeedback). This tutorial is a good on on using the Johnson Decade Counter.

The Johnson Decade Counter decreases the pins used to control the LED array from 3 to 2 and eliminates the need for current limiting resistors (though still likely a good idea) since it can only output 10mA per pin. Unlike the 595 shift registers used for the main screen LED Bar the 4017 requires us to use rapid switching for persistence of vision – only one LED can be lit at a time.