Working on my first design, a timer person 's light for Toastmaster 's

[G+_Thomas Kregel]

Working on my first design, a timer person's light for Toastmaster's.

I will use a 4 position switch for off/red/yellow/green. Stopwatch is not wanted as part of design. Staying with very simple user interface.

 

Questions around voltage.

1 Can I use a 9-volt battery to run my Arduinos or would it fry them?

2 I would like a battery driven device that uses led strips, but they require 12 volts. That would be a a lot of AA's. or 2 9 volts batteries? Other than normal LED's is there another option?

3 Does anyone know a good design to add a countdown timer that shuts battery power off in a fixed number of minutes?

 

Thanks,

Harvey

[G+_David Peach]

1. Yes, you can use a 9V battery to power an Arduino.

2. You can get 5V LED strips. As long as you don't use too many, you can power them through the Arduino.

3. Hmm, not sure, but you will probably want to look at a Real Time Clock (RTC) module as part of this build. Maybe you can use it to turn the Arduino off.

[G+_Bob Shields]

David Peach The RTC is best used when there is a requirement for the actual time-of-day or date. In case this, I think the concern is for a "relative time" or duration. I think you can get by with the Arduino millis() function: save its value at start, then just check the difference between that and the current value somewhere in the loop(). (Unless, of course you need more than 50 days duration, which is when the mills() counter wraps around...).

[G+_Thomas Kregel]

Bob Shields Thank you Bob. That sounds like to best way to count down, as you said , just relative time. How would I tell the Arduino to go to sleep then? Is it as simple as having a return in the main loop?

[G+_Thomas Kregel]

David Peach Thank you David! Nice to know I wont fry the Arduino. I was looking for a 5 volt LED strip on Android and found one listed as 5, but in the picture of the strip close up it said 12v at the connector. May be the picture was the wrong strip.

[G+_Bob Shields]

You may need to refine your definition for "sleep". There are Aduino states that require a reset to restart the processor. There are other low-power states which can bring the Arduino back to full processing with an interrupt. But note that the inefficient regulator as well as the USB port will probably eat more juice than you'll save by quiescing the processor. I'd search for "Arduino sleep mode" for better explanations than I can give.

 

But as far as LEDs goes, I would not choose a "strip/roll". If you just want a single colored lamp lit, you could either buy individual LEDs or a single RGB LED (same amount of wiring either way, but only 1 hole in the box for the RGB). If you want to "grow" this into something fancier that takes advantage of all that Arduino capability, I'd look at the NeoPixel LEDs available at https://www.adafruit.com/?q=neopixel. They have singles, strips of 8 or more, rings, etc. They also provide a lot of Arduino code for driving them.