I am new to this so forgive me if I seem a little ignorant. I’m trying to find out how to build a mini timer. I have a little background in electronics but nothing more than a home hobbyist. I also officiate lacrosse and need to build a timer small enough to fit on a belt around my waist during games. The switching pattern would be as follows. Using a three position toggle switch on-off-on. When switched to one on position it will start a timer that in twenty seconds will set off a buzzer, to turn a buzzer off you will need to the switch to the off position . When switched to the other on position it will start a timer and after 100 seconds will set the buzzer off, once again you must turn the switch off to stop the buzzer. Of course it will have to be battery operated and once again small.

Can anyone tell me how to wire this and what materials I will need? Where things can be purchased and if there is any wiring diagrams that I can get off line?

 

I'm guessing $55 is outside your budget? It won't be simple to design an accurate one that you would be able to build. It can be done easily with a microcontroller, but you would have a lot of first-time overhead (e.g., a programmer), and you would have to learn how to program it.

 

You can do something like this on a PSoC device very very easily. Search PSoC miniprog on google or at digikey, you will find a really cheap programmer.

Basically, you would set up the crystal oscillator on chip with two caps and a crystal. Then, you'd run this clock signal through the on chip dividers, then into the many counters available on chip. You just set the count for X amount of clocks in, then you will get an output. You just need a very simple input read via software, then initiate the counters, etc.

Steve

 

A 555 timer can be used for a relatively slow clock (1 Hz) and then you would need counters for up to 20 an 100 (or half that if you can get the 555 timer down to 0.5 Hz), then an output circuit to handle the counter outputs and drive a buzzer/sonalert.

The above is the basic idea and if you do not understand it sufficiently to do it yourself, I doubt anyone is going to take the time to design (and build) it for you.

 

A 555 timer can be used for a relatively slow clock (1 Hz) and then you would need counters for up to 20 an 100 (or half that if you can get the 555 timer down to 0.5 Hz), then an output circuit to handle the counter outputs and drive a buzzer/sonalert.

The above is the basic idea and if you do not understand it sufficiently to do it yourself, I doubt anyone is going to take the time to design (and build) it for you.

I wonder if a 555 would be accurate enough for lacrosse. It probably depends on what level he is ref'ing at.

 

I'm with Ron H on this one. Sports such as Lacrosse demand extremely accurate timepieces, and they have to stay accurate regardless of temperature, humidity, battery level, etc. If your timer is off by so much as a few hundreths of a second, SOMEONE will notice and call you on it - and then you'll have a flock of angry Lacrosse players screaming for your head - or even worse, those who placed wagers on the outcome of the game.

Building a timer circuit is easy. Building an accurate timer is not easy, nor trivial.