This is a draft. I don't have pictures yet...

Swimmer? Learning? Either way, clearly see your splits.

This project is a cheaper version of MichaelH814's: instructables.com/id/Large-7-Segment-LED-Pace-Clock. That project was inspired by the $100 dollar pace clock by mjacobson1: instructables.com/id/100-Pace-Clock-or-Wall-Clock.

Mouser or DigiKey

$3.54 - shift register

$3.2 - 15 Ohm resistors (8*4 = 32)

$ - SIP (single inline package)

https://www.mouser.com/ProductDetail/Bourns/4608X-...

Amazon purchases

http://a.co/eza44U3

9.88+13.86+5.99+7.99 = $37.72

Supplies (materials purchased at Home Depot)

$11.28 FOAMULAR 1/2 in. x 4 ft. x 8 ft. R-3 Square Edge Rigid Foam Board Insulation Sheathing

$6 - corrugated plastic sheets (semi-transparent)

$3.24 - double sided tape (permanent)

$3.72 - 2x4s ($1.24*3)

$2.50 - matte acrylic paint (8 fl oz)

$2.97 - E6000 glue (2 fl oz)

$2 - acrylic latex caulk, silicon sealer (5.5 oz)

Wood screws 2-1/2" (8)

Electrical tape

Wire

Equipment

$0.77 - foam brush (4 piece set)

Soldering iron

Straight edge

Box cutter

Drill

.

Total cost from above < $70

Step 1: Step 1: Frame/enclosure

Cut the wood. Screw. Apply spray paint.

Step 2: Step 2: Inside Pandora (the Box)

Cut 2-3 foam pieces to fit tight within 12" x 29". Cut 28 LED strips (5-6" wide).
Use one foam board as a backing (back-board) for the LED strips. Lay out four 7-segment displays with a gap at the ends. It should go something like 0.75"→6"→7.75"→13"→14.5"→16"→21.25"→23"→28.25".
Apply double sided tape to the middle of each LED strip.
Mark and cut squares out of the second foam board as channels for the LED lighting.
Also cut 1" colons.
Do not spray paint the foam! It will melt and deform. Instead, paint the cutout board with black matte acrylic paint.
Make sure the LED strips align with these new grooves. Adjust if necessary.
Lift up the ends of the LED strips and drill holes on the back-board.
Glue the two middle squares of each 7-segment display. (Any glue will do. The E6000 is a bit extreme.)
Before binding those foam boards together:
- Soldier 12" wires to the ends of the LED strips. Feed the wires though the holes, and glue the boards together.

If you're feeling insecure about your life, caulk the sides of the foam boards to the 2x4s. I didn't.

If the wires are bullying you, smother them with generous amounts of tape and glue.

Step 3: Step 3: Swag Them Shift Registers in to Curb the Rat Nest of Wires

Make a grotesque, but lazy, ground bus (connected to an Arduino ground).

Pinouts

Colons - Arduino 5V and a ground bus

See picture for the rest.

15 Ohm resistors (8*4 = 32)

The input/output pins are GND (Ground)

LAT (Latch),
CLK (Clock)
SER (Serial data)
5V (Power for the driver IC)
12V (Power for the 7-segment display)

Electrical engineering info

TPIC - Three Pole Iron Clad (electrical switch point)
wikipedia.org/wiki/Shift_register

This is the hard part. Look at the 6C596 shift register datasheet. Absorb it. This may take multiple attempts starting with eye absorption with the eventual goal of brain absorption. Hang in there.