LED Time Circuits

home made time circuit display
I know it's a common project, but I thought I'd make my own Raspberry-Pi powered Time Circuits, looking similar to those seen in the Back to the Future movies.

The goal is to have three calendar/clock displays (red/green/yellow) that you can set via a keypad. In addition there will be a flux capacitor, a spedometer, various meters, and any other random features that seems fun at the time.


Build directions: time_circuit_build.pdf

The Raspberry-Pi controls everything over i2c. The Pi (running Linux) is a bit of overkill, as any board that can keep time and drive an i2c bus could run things.

The display is run by a series of HT16K33 chips (I use the breakout boards from adafruit). Each chip can run up to 16x8 LEDs plus read a keypad matrix.

For the displays I use Kingbright common-cathode LED displays. I ended up buying direct from them as it was hard to source red, green, and yellow displays of both 7-segment and 16-segment types all from the same place. In the end the yellow 16-seg are of type PSC05-12 and the red and green are of type PSC05-11 and the pinouts are not compatible. This is unfortunate because it means I'll need separate PCB layouts.

More details/directions on building will be provided as I finish constructing each segment.


The displays will not match the version seen in the movie exactly.

There are some good reasons for that ( the month names as displayed in the movies aren't possible with off-the-shelf LED displays).

Also I like to think Doc Brown himself was a bit of a hacker (although a bit of a perfectionist) and thus any rebuild he did would vary as he thought up improvements.



Flux capacitor and power displays. Note the analog and other meters as power-up happens. Sorry for the backlit video, I need to build a case so I can angle away from the window (or else find a better camera to record with).

Older demo including sound:

A much older run-through of the breadboard prototype showing current time and then setting the date to various important times:

Other older videos can be found here.

Build Log

3 June 2014

Prototype of the case assembled:

The case itself is made up of scrap wood and aluminum standoffs, with holes (poorly) drilled by hand with a power drill. Functional (barely) but not very pretty.

6 May 2014

I finally got around to finishing and ordering the keypad PCBs.

I cut out the openings in the keypad case by hand. Sadly they aren't aligned very well, despite the fact that I made a paper template to guide the drilling. Maybe time to get a CNC mill or at least a drill press?

Testing the circuit board. The holes for the diodes were way too small. In the end I sort of surface-mount soldered them in place, I'm sure that's not good long-term.

The assembled keypad. It was a pain getting all those wires in, I should have used thinner wires and maybe socketed everything. It works though!

A snapshot of the current project area:

8 April 2014

The flux capacitor is more or less finished:

Flux capacitor and d/a board bringup:

6 March 2014

The spedometer and flux capacitor circuitry as well as most of the power display are functional. Waiting for a shipment of better LEDs, and then I need to make some more circuit boards and drill holes in some cases.

26 February 2014

I had some visitors to my work area:

You can see the Lego time circuits. The date is set to 1958 when the first Lego brick was made.

I couldn't decide on the old or new license plate. You'll note I have Mr. Fusion installed, as well as the BTTF3 vacuum tube circuitry. I'm using the old tires over the red whitewall ones.

That's a load-bearing flux capacitor. Also Doc's hair is too big for the door to close while he's driving.

18 February 2014

Yellow display bringup, as well as the power-converter board. Also took some time to clean up the keypad rats-nest.

12 February 2014

An annotated picture showing status at the time. There's a battery-backed real time clock so you can keep time when disconnected from the network. There's a speaker/amplifier for sound effects and music. Also some power circuitry to bring in a dedicated 5V/1A supply to the LEDs, as driving all of this from the rasp-pi 5V output started getting dim and glitchy.

28 January 2014

Bringup of the green display. It has the same layout as the red display:

27 January 2014

First bringup of the red display! Amazingly everything worked, except for the 16-segs had segments R and S reversed due to lack of alphabetical order in the data sheet (note the 'N' in JAN). Easy enough to fix in software.

Time circuit malfunction! This is what I got after running the old software on the breadboard after re-wiring to match the PCB version of the display:

21 August 2013

First prototype of the display with all segments on as a test. I have a mix of red/yellow/green just to be sure everything is working.

Source Code

All the code can be found on github: https://github.com/deater/vmw-meter.git

git clone https://github.com/deater/vmw-meter.git

Look in the time_circuit directory.

It is fun when your source code has statements like this:
	if ((current_speed>=88) and (current_power>=121)) time_travel=1;

Other projecs at the VMW Hardware/Software Productions Page