Introduction: Table Tennis (Timeout / Warm Up) Timer
I practice Table Tennis at a local club called SC POVOENSE, in the beautiful city of Cantanhede in the centre of Portugal.
In table tennis, commonly know as Ping-Pong when practiced only for leisure, athletes have 2 minutes for the warm-up and 1 minute whenever they ask for a timeout (and each athlete can ask for one per match).
In bigger / richer clubs, whenever there is a timeout, the referee will put a Timeout Timer at the table. That Timeout box basically is a timer of 60 seconds with a countdown. We can see examples from some of the most know brands in this sport in the pictures.
Such a timer costs around $300 which I believe is bloody expensive. So I decided to give it a try to build my on.
Being a maker, but not someone skilled enough in electronics, I had to find a way to speed up the process. The natural choice would be to use an arduino but to be honest I haven't done anything on that field yet, so I started a different route and used a 555 timer integrated circuit from a DYI kit that I found online.
My approach does not include the visible count-down. I consider that the most important thing is to warn the players when the time is up. This is even more important when sometimes some referees may be amateur (and perhaps shy), and they lack the authority to force athletes to respect the rules, so this will naturally help.
Remember I wanted this to be very low cost, so the compromise I did (low cost assuming I don't have the visible countdown) seems pretty acceptable to me.
If I was doing it for the Timeout counting, I might as well include the Warm-up period in the same device.
The video shows the final outcome.
Step 1: The DYI Kit Timer
I bought from eBay a DYI kit that basically uses an 556 Integrated Circuit (IC) which according to their explanation is basically two 555 ICs in a single IC. The idea is that by regulating some resistance we can control the countdown time and the buzzer time.
I bought two of those kits as I thought that it would be easier to configure one for the TimeOut (1 min) and another for the Warm up (2 min).
I built them following the detailed instruction without much hassle.
I've tested them and used a clock to adjust the variable resistors until they were behaving as I wanted (60s countdown and 3 second buzzer time; and 120s countdown and 4 seconds buzzer on the second kit).
Step 2: Changing the DYI Kit
1) The kit had a red led that lights when it is counting down. I thought a green led showing it is working would be nicer. I had some old leds at home, I've checked online if the voltages were the same and as they seemed to be, I just replaced the red led for the green led.
2) The second thing I did (and in order to reduce costs) was to try to do both the Timeout and Wamup settings using just a single circuit.
I started by measuring the variable resistors value in each circuit to get the number of ohms needed at each circuit. Then I've looked for the equivalent fixed resistors and I've chose the minimum value needed for each circuit.
Then I've added a single switch (2 circuits - one for the timer and the other for the buzzer) and according to the switch position I've added the remaining resistors to have the maximum value of ohms needed when the switch was on each position (either Timeout or Warmup). In haste, in one of the positions of the switch I had to do nothing and the resistance was already the needed for one of the positions; in the other position, the additional resistors would be in series with the base ones and the sum of them would give the value needed for the second circuit.
Activities 1 and 2 are depicted in the picture.
3) Finally I thought that while the buzzer is working, it would be nice to light up some red leds also. I was not sure on how to accomplish this because of the current (amperage) needed but I decided to experiment and see what would happen. So I've looked for 4 red leds and searched online how to include them looking at the schematics.
From my research, connecting them in parallel with the buzzer would be the best option. So even tough I've also experimented putting them in series, I went for the parallel connection. I've soldered a 390ohm resistor to each led on its positive pole (I think online the recommendation was to use 370 ohm but I did not had such resistors at hand) and I've tested it. It worked and because this works only for a couple of seconds while it is buzzing, I doubt I'll have many problems. But time will tell. Obviously, use it at your own risk as I am no expert in the field. I've drilled some holes in empty places in the circuit board and just using solder I've patched all the connections needed.
Step 3: The Box
For the box I've just thought that it would be nice to try to get something similar in shape to the original timers from the big brands.
I went to a regular chinese drug store (very common over here) and just bought a wood enclosure for this purpose.
I also bought some tiny magnets and glued them to keep the box closed.
Apart from that, I had to drill the holes for the switches, the leds and the buzzer. Here I did a mistake which was to drill first and only draw the artworks afterwards which became much harder to fine-tune. But eventually, Ive sorted it out.
Because of the wood thickness, in some of the holes (for the switches at least) I had to use a knife to reduce the thickness to ensure the switch would pop up on the other side to allow to secure it using the provided nut.
Step 4: The Artwork
The artwork was basically an exercise of opening a powerpoint file and start drawing an object including all the sides of the box.
The only complicated one is the top because of all the holes. In the end I had to redo it twice to make it acceptable.
Then I went to a printing facility and printed (and cut the holes) the layout in self-gluing vinyl.
Lessons learned If I was doing this again:
- vinyl is not the best thing to glue in wood. We had to spray some lacker first to ensure it would glue better and also heat it up a bit by using an heat gun or hair dryer. Another option would be to paint the box before putting the vinyl. All that helps to glue it better and remove the wood embossing.
- it would have been better to only drill the holes for the switches and leds at the end. It would have given more flexibility.
- Most important, the vinyl should have been protected with a sheet of transparent plastic to make sure that the black ink does not get scratched. Because I did not do that (and also because of the leds being a little bit out of the box), I decided to put some pads to protect the vinyl and keep the box steady. Could look better, but it works.
Step 5: Final Assembly
I bought an handle (one from drawers that you can get in a drug store or Leroy Merlin kind of store) and applied it to look more like the original timers.
I've also changed the power on/off switch type and also the start push button to have them all look the same.
I've used some led holders to give it a better finish in the led holes.
In the end, I've spent around 40€ doing this (even less because I had the resistors, leds and such at home). Electronics 25€ (and most of it were shipping costs from the UK to Portugal) and 15€ for the box and artwork.
Hope you like it.
Do let me know if you have doubts.