Small project for uni tennis club

Thread Starter


Joined Jun 17, 2014
The issue- Our tennis club has an issue with player rotation. Basically the players on court don't get off the court to let the players waiting their turn on.

The idea - Create/Buy a device that every player who is waiting can activate when they begin their wait. This device will activate a light after 10 minutes which will indicate to everyone that it is time for player rotation.

Preliminary thoughts: Since we have 6 courts and 4 players to a court, we will need 24 of these devices. These devices need to be battery operated. Perhaps a battery operated time switch connected to a light bulb. Upon pressing a switch, the timer should start and the light should flick on in 10 minutes for 2 minutes and then switch off, unless it gets pressed again, then the whole process should repeat.

Resources: Time and money

If anyone has any advise, ideas or suggestions for a solution we would really appreciate it. If you need us to clarify anything, please don't hesitate to ask

Thank you


Joined Jan 21, 2013
Don't know if you can still get them but I have seen mechanical count-down timers which you wound round to a given time (10 mins in your case) and then it ticked down to zero at which point it would open/close some contacts

In fact something like this -

Thread Starter


Joined Jun 17, 2014
@tshuck: The reason behind not using a kitchen timer

a) They create noise instead of turning on a light
b) They can be wound to less than 10 minutes, it isn't standard. And hence, players can tamper with it to get to play sooner

@sirch2 The reason for not using the mechanical count down timer is reason b written above

We will use something that has to manually wound if it comes to do that. Ideally we would like a standalone light bulb with batteries installed under it. The switch would be installed in such a way that the light could be pressed in, which would result in it switching on in 10 minutes time.


Joined Oct 18, 2012
Fair enough.

Since a coarse timing would probably suffice, I could see this being done with a few (one?) monostable 555s, with a button to (dis)charge a timing capacitor.

Bill_Marsden has some neat stuff pertaining to 555s on his blog.


Joined Oct 15, 2009
I wouldn't make it with batteries as thats just additional cost over time (or use rechargeable) and include a battery indication of some sort.. I'd assume this is outdoor and I'd assume there is a light pole with AC available at it vs batteries.

Do you have a loudspeaker system there?.. Maybe just a 10 minute "horn" from that to globally cover all the courts at one time.. Sure saves quite a bit of money/time doing that..

There do seem to be a few similar devices on the market already though.. from $10 to $250

Or just build more courts ;)


Joined Jan 21, 2013
You could have green light when the clock is set and a red light when the time expires. That way the players on court can see that someone is waiting and if the waiting players set the time too short the on-court players will know - give or take the length of a rally.

All that said, technological solutions are generally not that successful in dealing with human relationships. Better to educate the players in good manners.


Joined Apr 16, 2010
I don't see how the bracelet is going to communicate with the appropriate light. I also don't understand whether a given player is waiting for a specific court or just for any open court.

A better (in my opinion) solution would be a timer associated with each court. Players who are waiting would simply press a button associated with a timer for the desired court, which would expire and light a signal after the waiting time is up. If you wanted to add to this idea, you could equip each court with a digital display to show how much time is left before the court becomes available. Further enhancements could include another digital display that shows how many groups of players are waiting for a given court. The ultimate solution might be a combination timing/allocation system that allows waiting players to press a single button, and thus be in the queue for the next available court.

Elec_mech, a regular on this forum, has done some work on countdown timers, and would be able to help define how a suitable system could/should work.


Joined Nov 12, 2008
As sirch2 mentioned, I'd be concerned about the human factor. We can help you come up with a number of options/circuits, but I think the problem and how you foresee the solution being implemented need more defining.

Since we have 6 courts and 4 players to a court, we will need 24 of these devices.
Huh? Are you picturing bracelets as tracecom mentioned?

Let's step back a bit.

You said tennis club. For some reason I missed that initially and pictured you managing a tennis court which would make this a bit more difficult from the human factor side. So this is one club where everyone more or less knows each other and gets together to practice on six courts, four per court?

How many people are waiting when all the courts are full? In other words, how many groups of four are wanting to play if everyone shows up?

Do you have to share the courts with others (non-club members) or do you more or less have all six courts to yourselves when you get together?

Is ten minutes enough time to keep people happy? Obviously there is a compromise to be made between the time someone wants to play vs. the time someone is willing to wait to play.

I assume since this is a club, you don't own the courts and thus you can't tamper with any electrical power going to the lights on the court. I also assume you may want to use these devices on other courts or would at least like the ability to do so?

For the sake of thoroughness, are there electrical outlets on the courts near the net? Doubtful, but I have to ask. This allows us to expand or narrow your options accordingly.

How long do you typically play when you meet, e.g., 30 minutes, 1 hour, etc.?

If you went with a 10-minute timer and light, where will the light go so that active players will see it and how will waiting players activate it?

I'm picturing something that is near the net so the active players will see the light, but I doubt you want waiting players coming up to the net to turn the timer on. The opposite would be having the light located wherever the waiting players are, but then they'd have to tell the active players when time was up which could lead to heated exchanges once in a while. Of course, nothing says active players won't ignore a light on the net. :)

If this is how you envision this, then a remote would be ideal.

If you want to get crazy, you could develop something that monitors each court simultaneously (assuming each session starts at different times from one another) so that the first court used is the first court freed when players are waiting. Think of going to the post office and waiting in one line to see one of three workers vs. going to the movie theater and attempting to pick the shortest line (which could take longer depending on the people in front of you). In the first instance, everyone gets seen in the order they showed up. In the second, you're competing with others to get in next and you may end up waiting longer than someone who just showed up. This would require some serious thought on implementation, so I leave it up to the OP to decide if it is worth the effort.

If everyone shows up and starts at the same time, you could make one timer with a buzzer. When the buzzer goes off, all six courts switch players. This would lead to less dissatisfaction I think, but hinges on everyone starting and switching at the same time.


Joined Nov 23, 2012
No matter now complicated or simple, fool-proof or tamper resistant. Unless the device picks up the violator and throws him off the court, it is not going to work any better than the current system. People have to follow rules.

My old club had a chalk board and a clock that everyone could see. An arriving player would write the current time on the board with his name. Once the clock passed 10 minutes, he/she would get a court.

If there is already a player waiting in line, the newest player must write 10 minutes more than the person ahead of him.

Courts were numbered and each team would start on court 6 and move to the next lower number court when a new pair arrived (assuming the courts were empty). The team on court #1 would have to leave when the arriving player waited for 10 minutes.

Everyone gets at least an hour of play.


Joined Sep 17, 2013
A simple timer will take no account of the length of time players have been on court. To ensure fairness, those who have been on longest should come off first to make way for waiting players; i.e. a 'First-On-First-Off' system is required.
I share GopherT's views on human nature. Court-hogs will simply ignore timing lights.