Build the Circuit

LCD shutter panels work like this: when you apply voltage across the terminals of around 4V, the liquid crystals will arrange them selves in such a way as to become opaque. When the voltage drops down to around 1V the display will become transparent. 

This can be done very simply by using a battery to darken the panel and then a resistor to drain the charge and go back to transparent. But for a smooth fading effect we'll use a microcontroller to ramp the voltage up and down.

The Trinket 5V is perfect for this task! It has three pins that can provide a PWM (pulse width modulation) signal, which is essentially a digital way to approximate a smooth analog signal. By sending a PWM value from 0 up to 255 to one of the panel's terminals over the course of a second, (with the opposite terminal across the longer dimension of the panel is connected to ground) the panel will gradually fade from transparent to opaque over the course of a second.

Start by soldering the BAT pins between the LiPoly charger and the Trinket.

Next, trim one of the outer legs from the switch, and then bend the two remaining legs to connect the switch onto the Trinket GND and one of the charger GNDs, then solder them in place.

Now, you can connect one of the panels. Measure out one length each of black and yellow wire long enough to run from the board to the panel in roughly the final spacing based upon your box dimensions -- abut 4" should do. Strip the ends of a bit of insulation and tin the wires.

Then, solder the yellow wire to Trinket pin 0 and one LCD terminal (they are not polarized, so any one is fine).

Then, solder from Trinket GND to one of the LCD terminals that is on the side farthest from your yellow wire's connection. See the diagrams and pictures for clarity.

Plug in the battery and flip the switch -- you should see the Trinket's power LED light up, but the panel won't change yet until we program the Trinket.

Solder a 6" length of green wire to Trinket pin and an 8" length of blue wire to pin 4.

Solder the green and yellow wires to the two remaining LCD panels respectively. Then, solder short black wires between grounds of the LCD panels.

Next, let's wire up the hall sensor to detect our magnet. Use 10" lengths of red, black and white wire for this.

Strip and tin the wires, then slip short lengths of heat shrink tubing over them to isolate the sensor legs.

Solder the resistor between the outer legs of the sensor, and then solder the wires to the sensor legs like this:

  • Red to the left (leg 1) (when looking at the "front" of the sensor)
  • Black to center (leg 2)
  • White to right (leg 3)

Here's how the Trinket will use the Hall effect sensor:

Connect power to pin 1 (all the way to the left), ground to pin 2 (middle) and then a 10K pull up resistor from pin 3 to power. Then listen on pin 3, when the south pole of a magnet is near the front of the sensor, pin 3 will go down to 0V. Otherwise it will stay at whatever the pullup resistor is connected to, in this case we'll use Trinket pin 2. Nothing occurs if a magnet's north pole is nearby (unipolar).

This guide was first published on Apr 01, 2017. It was last updated on Apr 01, 2017. This page (Build the Circuit) was last updated on Sep 17, 2019.