I have been contemplating this project for a while and am suprised noone
else (that I have seen on the web), has tried it.
I want to make a digital speedometer and/or tach for a regular run-of-the-mill
mountain bike. I just DON'T like the lcd stuff.
I can work around the being in the sun issue. It kind of goes with my
design ideas.
My LCD watch runs 2 years continuously on a button battery.
Years ago, watches had an LED display. They were blanked most of the time to save current then lighted dimly for a moment when you pressed a pushbutton.
AA cells would power an LED speedometer for 4.5 hours. The wagon-load of replacement batteries would be a drag to carry around.
If the speedometer shows 88.8km then 22 LEDs are lighted with 25mA each.
The total current is 550mA.
Well I would like to use as small of battery as possible it is a project for my
kid. I thought it would be cool to have an led speedo on a bike. So nothing
too big but something enough to power the display.
I would make sure to tell him not to have it on ALL the time for the replacement reason. I would be something better used towards the end of the day when the sun isn't so bright.
not to dampen spirits, but considered getting a wireless commercial speedo? £40 and u dont even have to put it on the bike (usually works from inside my backpck when i forget to put it on)...
That would work but a home made unit could potentially do other cool stuff like log your speed at differend parts of the race as well as take your maximum and minumum speed.
LCDs take virtually no power so a simple magnet connected to the wheel and coil attached to the fork might provide enough power to work it.
Multiplexing LEDs reduces their duty-cycle which reduces their brightness by the same amount. So the current must be increased to keep the same brightness as just one. You gain nothing.
I think the real question is what does the human eye perceive. Besides the persistance of vision effect, I think there a highly non-linear response to brightness that comes into play. Multiplexing LEDs (and LCDs, VFDs, Nixie tubes) is used all the time to produce acceptable looking displays with considerable power savings.
I think the real question is what does the human eye perceive. Besides the persistance of vision effect, I think there a highly non-linear response to brightness that comes into play. Multiplexing LEDs (and LCDs, VFDs, Nixie tubes) is used all the time to produce acceptable looking displays with considerable power savings.
No, it's used to reduce the number of connections required, it's not about power savings - as suggested you would normally run the displays at the same average current.