I don't know how big is the DIY community here but I thought it would be nice to reach more bike enthusiasts anyway.




It is far from being waterproof but..

More technical details here https://zenontech.wordpress.com/2015...okia-1100-lcd/

That's a pretty fun project. I wouldn't probably use Arduino for a low power embedded system, as that imposes pretty bad power drain at all times. If you program it directly in C you'll be able to just trigger on interrupts when the sensor hits and your CPU can be drawing effectively zero power 99% of the time. Also, you can avoid the usually horrible linear regulators and such that are in the system. The ATMega chip will run on unregulated power straight off the battery and you can use a 3.3v LDO regulator on the display to keep the power drain extremely low.

Pretty cool project in general, and I would probably have started with Arduino to get everything going, but I definitely would get rid of the Arduino part of it and code to the bare metal before deploying it for real.

I used Arduino programming on a STM32 board. You can add any bare C or even asm trickery alongside for things that are not directly supported by Arduino (interrupts, sleep and any other mcu config stuff), while still having Arduino do the bulk work clean and easy.

So I actually used an interrupt for the sensor, but no sleep modes for now except powering off the LCD.
Even after optimizing it for low power consumption I don't expect it to work off a CR2032 anyway because the LCD (or rather the time spent sending data to it +backlight) would draw much more than the cheap odometers. I think a rechargeable 1000mAh LiPo cell would be best.


BTW, I've been thinking what if Nokia made available the tools to write firmware on the 1100.
So you could have the whole rugged phone case with everything that's needed, and possibly using one of the built in connectors to attach the sensor without any hardware hacking.
Or any other cheap monochrome LCD phone..

I've got one of those Nokia displays I've played with a bit but I haven't measured current draw; what do they pull?

I started messing with OLED displays and I was surprised that the one I have (128x64 res I think) only pulls about 20ma. That's way too much for an LCD unless the backlight is on but for an active display it's pretty stingy. Hopefully you can turn the backlight off on yours.

You could probably drop the clock speed quite a bit on that unit and still run just fine. Dropping down to 4MHz saves a lot of power on ATMega chips.

Good call on using an interrupt for the sensor, at high speeds polling would totally miss it.

The N1100 LCD draws about 250uA in normal mode (300uA at high refresh speed like 10Hz) and 0.2uA in power off mode. Not sure what the average MCU consumption would be with all the optimizations, but I think it would be higher.
However night rides would really suck the battery as the backlight needs around 15mA.

You can pretty much rule out OLED for such applications as they are not visible at all in the sun, let alone the power consumption.

And no, polling it at a few MHz would not miss any sensor signal but it would be tricky to also update the LCD in this time.