Flashing metronome circuit required

[Henno]

Hi gurus,

I am trying to knock up a battery powered LED flasher cct for timing for my dragon boat team. I have googled around and realise that it will probably be a simple 555 IC controlled by a variable resistor. What I'd like however is to be able to include an LCD that tells us the BPM. We'd like to paddle at about the 65-66 BPM but whenever I time us with a stopwatch we are way over or under this.

It would need to be able to power enough LED's to be able to be seen by the paddlers in the back seat which is approximately 12 metres away from the drummers seat where I'd like to attach this invention.

Thanks in advance for any replies guys and gals.

Mark in Oz

[Thomas W]

The LCD can be controlled by a microcontroller, for example the Arduino http://www.arduino.cc/ , or a PIC http://en.wikipedia.org/wiki/PIC_microcontroller . These could replace the 555.
How do you register beats? You could feed single beats to the microcontroller and let it calculate BPM.
What's your requirement for the maximum weight of the battery? A microcontroller board consumes more energy than a 555 but you can make it do much more for you.

[Henno]

Hey mate,

Thanks for your reply. I don't really know what you mean by how we register our beats. I'd like to set a bright light to flash once a second and the screen to read 60 for example. This would only have to be visible to the two paddlers in the front seat and they'd be able to crank it up if we felt that was too slow. I'd imagine it to just be controlled by a vol pot of some sort.

Maximum weight of the battery is not too much of an issue. It could be as large as a 12V motorcycle or home alarm battery if necessary. I'd house it in a waterproof pelican box or something. I'd gladly forego a bit of weight for accuracy. I'd hate to build the thing and when I set it to 60bpm and time it with a stop watch to find out it was actually over or under.

Cheers
Mark

[Thomas W]

Ah... I thought you wanted to have your actual rate shown on the screen, but that would also be more difficult to make.
If you had some sort of sensor to register your beats and let the electronics show the rate on the LCD you would know if you were paddling too slow. But again, showing a rate without feedback is easier to make.
A vol pot would be a good way to set the rate. How accurate do you want the setting to be? +/- 1 BPM? Most pots are continuous, so you'll have to convert to steps, if you use a microcontroller as the 'brain' of the circuit.
With a motorcycle battery there should be enough energy. You can actually run a small LCD nonstop for years from such a battery.
The accuracy should be sufficient with a microcontroller:

Typical clock crystals used in microcontroller devices have inaccuracy of less than 20 ppm which means less than 10 minutes per year.

http://users.tkk.fi/jalapaav/Electronics/Pic/Clock/index.html

What do you want to build the circuit on? Stripboard, breadboard, PCB...
And what size of LCD screen do you want? Maybe you can use an iPhone with a special app for all of this

[Henno]

Ah I see what you thought I was after now. It would be a pain to turn our own paddle rate into a display. We basically want to paddle at the same rate as a flashing light that we can control from the front of the boat.

I was wondering if an up button and a down button may be less twitchy than a vol pot scenario.

As for the size of the screen the larger the better. Maybe 40mm high for the numbers at least. The bank of LEDs should be nice and bright as well as it will be in outdoor environment in sunny Queensland.

I'm not scared of a soldering iron so breadboard would be fine. The more accurate the better. If it is reading 60BPM and I time it and we got 62 flashes in 60 seconds it won't be much good. I suppose if was always under or over we could time it and allow for the variation though. How accurate can you buy?

Thanks for this
Mark

[I_Daniel]

Your requirements are quite sophisticated.

A simpler circuit would be to use LED striplights/spotlight which are very bright and/or a beep from a loudspeaker.

A 555 IC is quite stable and would probably be your best bet. Using a tantalum or similar high quality capacitor and a good quality resistor in the timing circuit the drift in frequency should be negligible.

To initially set the timer accurately you will need to use a frequency counter.
You could possibly adapt one of those electronic metronomes to meet your requirements.

[pebe]

I think a micro controller would be the easiest way of providing what you want.

Imagine a row of up to 10 LEDs as indicators from the lowest beat rate to the highest. For example, a lowest of 63 and highest of 68bpm would give an indication in 0.5bpm increments.

At startup, the middle one at 65.5bpm would flash at that rate, with equal on/off times.

Two push buttons would be used to increase or decrease the rate, and the new LED selected would flash at that rate. So the flash rate would keep you in time and the LED that was flashing would tell you what the rate was.

A PIC with 12 i/o ports would do the job. If your LEDs needed no more than 30mA then the IC would be a standalone unit, or if more current were needed (most likely) transistor drivers could be added.

[Thomas W]

I was wondering if an up button and a down button may be less twitchy than a vol pot scenario.

Yes, a couple of buttons would be better.

As for the size of the screen the larger the better. Maybe 40mm high for the numbers at least.

You could replace the LCD screen with two of these, and still have numbers displayed:
http://australia.rs-online.com/web/p/le ... t/4516571/
(Shop around to find the exact product you want)

The bank of LEDs should be nice and bright as well as it will be in outdoor environment in sunny Queensland.

You would have to experiment with different types of LED's out on the water to find a type that is sufficiently bright. The more money you spend, the brighter, as you have enough power with a motorcycle battery.

I'm not scared of a soldering iron so breadboard would be fine.

Then you should use stripboard instead of breadboard.
Or, I can draw a PCB for you if you want, when the circuit is ready.

The more accurate the better. If it is reading 60BPM and I time it and we got 62 flashes in 60 seconds it won't be much good. I suppose if was always under or over we could time it and allow for the variation though. How accurate can you buy?

As mentioned earlier, 10 minutes per year, that's 10 * 60 = 600 seconds lost or gained when counting seconds non-stop for a year. That's pretty accurate