I built my own Track & Field countdown timer to help when I officiate track meets. It was MUCH cheaper than buying a timer from the major track & field equipment suppliers. Mine also displays time on both sides…theirs do too, but at 5x the price. Mine is battery operated, wall-pluggable(if needed), and uses a remote keyfob for operation. It’s programmed to do exactly what I want and need and nothing more.
T.F. Timer – NeoPixel Edition v1.0
I’m using Adafruit’s NeoPixel LED strips instead of buying pre-made boards…they are bright, cheap, thin, and lightweight. The timer box/housing will look a lot like an A-frame home with a flat roof. I’m using 1/8″, 1/4″ and 1/2″ thick MDF for the build as well as smoked acrylic to cover the digits. It is mostly glued together with wood glue with a few screws hidden away for some extra rigidity.
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Using NeoPixels also means I can make the digits as large or small as I want. This first version is essentially my working prototype. The segments are a bit further apart than I’d prefer, but I’ll fix that in my next version.
In Photoshop, I created a 7-segment clock image scaled to the needed size and printed on standard laser(black toner) printer paper. Print it reverse facing so when you place it printed side down it looks correct. I then centered the paper(toner side down) onto a 1/4″ MDF panel. Using Acetone(wearing gloves…safety first!), I wet a sponge and rubbed through the paper soaking into the wood. It doesn’t take much and works pretty fast. This will transfer the toner image onto the wood. If you overdo the soaking, the toner will bleed and spread so be careful. I really don’t care that it looks too messy, I’ll be painting over it anyway when I’m done. I did this to help align all the cut NeoPixel strip segments that I glued and soldered together. Next time, I’ll make my digits smaller so the LED strips will be closer together.
I cut the strips into 3 LED segments and used Super Glue to glue them to the board. Just a small drop on the board opposite each LED; 3 drops per segment. Hold it down for a few seconds. It sets up FAST on MDF so work quickly and have your alignments prepared. When it dries, you’ll need a chisel to pry them off….so don’t screw it up!
I soldered all the segments together using 24 gauge Artistic Wire. 24 gauge wire is rated for up to 5A. I won’t be pushing near that much so….no worries.
The plans are to cover the LEDs with stickers and paint the entire board, copper and all, with black spray paint. Next time I’ll buy the NeoPixel strips that are black and not white. Oh well.
I finished soldering the 2nd side last night. It only took 3 hours, much less than the first side. I also confirmed that I can feed both sides from the same Arduino pin so they’ll display the exactly the same at the same time….as desired.
Once I had them all up and running, I measured the power usage. I measured a maximum .98 amps just from the 2 clock boards while the timer was counting down. The LED display brightness was set for 200 out of a maximum of 255. I’m only displaying a single color, yet I was still surprised that the power consumption would be this low. I had over-estimated the power that I’d need! That’s a good thing…. I called Mouser and ordered a new/smaller UPS power supply module and will be credited for sending the other one back. (Note: I’ve had to call Mouser a few times lately. I gotta tell ya, their customer service is fantastic!
Tomorrow, I’ll cut the top, bottom, and sides of the box from 1/2″ MDF using my redneck table saw and begin glueing it all up.
I’m posting the build as I go, and once complete I’ll post all my Arduino code and other details about how this will be powered, etc.