bike project

[gizmo13]

hello all,

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.

Thanks for any help/advice anyone can give.


Craig

 

[Marks256]

Get a microcontroller, a magnet, a magnetic switch, and a few LEDs as well as a few 7Segment displays. Easy.

edit: oh, and you will need two or three pushbutton switches, some caps and a few resistors.

 

[audioguru]

Do you want to carry a heavy battery to power all the LEDs in an LED display?
An LCD display runs from a tiny lightweight button cell battery.

 

[HarveyH42]

Why batteries? Seems a small generator would work, only needs power when he's in motion anyway...

 

[audioguru]

The power used to carry a heavy battery is probably the same as driving a generator. A speed limiter.

One guy tried a fan as a generator. It was like dragging an open umbrella around. The power to light many LEDs must come from the rider.

 

[Marks256]

Oh i am sorry; i didn't know that leds required BIG batteries. I also didn't know that AA batteries were considered big.

 

[audioguru]

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.

 

[Marks256]

Yes, i see what you mean.

 

[gizmo13]

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.

Craig

 

[audioguru]

A 9V alkaline battery would power the LED speedo for about half an hour. You will see the display dimming as the overloaded battery runs down:

 

[Hero999]

Why batteries? Seems a small generator would work, only needs power when he's in motion anyway...

That's a good idea, the generator could act as both a speed sensor and a power source as the frequency varies with changing speeds.

 

[Marks256]

That's a good idea, the generator could act as both a speed sensor and a power source as the frequency varies with changing speeds.

So then would a simple frequency counter have to be made?

 

[Hero999]

Yes.......................

 

[pittuck]

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)...

 

[Hero999]

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.

 

[pc88]

If the speedometer shows 88.8km then 22 LEDs are lighted with 25mA each.
The total current is 550mA.

With multiplexing you can cut the current requirements way down - I've seen designs where only one segment at a time is illuminated.

I like Hero's idea of making a small generator to power the circuit. That would make a good science project.

gizmo - I'm not sure what you don't like about LCD displays. Have you considered an LCD with backlight or even an OLED display?

 

[audioguru]

With multiplexing you can cut the current requirements way down.

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.

 

[pc88]

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.

 

[Nigel Goodwin]

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.

 

[audioguru]

I use pulse-width-modulation in my Ultrabright Chaser projects as their brightness contol from very dim to full brightness.