Stopwatch does not measure time accurately

Projects General Guidance
1

Hello,

I am having some problems with a stopwatch. It seems to measure half the time it should. One reading should be about 2.5-3ms and the other about 10-12ms

I think the problem is with my fuses and the selected clock.

With fuses set to an external crystal (CKSEL = 1111 SUT = 01) I get about half the time. 1.2ms and 5.6ms

With fuses set to an internal oscillator (CKSEL = 0010 SUT = 10) I get about one forth of the time. That's about 0.6ms for the first reading.

If I enable CKDIV8 the Arduino moves so slow it is impossible to use.

I use an Arduino Pro mini 5V 16Mhz.

What am I doing wrong? Any help would be appreciated.

2

Reburn the bootloader, select Uno as the board type. Then Uno as the board type going forward.
Fuses will be reset to 16 MHz, external ocscillator. I burn all my 328's as Uno. Keeps like simpler.

3

Thank you for the reply but it did not work.

This is my UNO from boards.txt

uno.name=Arduino Uno
uno.upload.protocol=arduino
uno.upload.maximum_size=32256
uno.upload.speed=115200
uno.bootloader.low_fuses=0xff
uno.bootloader.high_fuses=0xde
uno.bootloader.extended_fuses=0x05
uno.bootloader.path=optiboot
uno.bootloader.file=optiboot_atmega328.hex
uno.bootloader.unlock_bits=0x3F
uno.bootloader.lock_bits=0x0F
uno.build.mcu=atmega328p
uno.build.f_cpu=16000000L
uno.build.core=arduino
uno.build.variant=standard

4

What am I doing wrong?

You have failed to properly post the code.

5

Hi,
Have you tried code with a NON MODIFIED 328?
That is written code for a stopwatch with a bog standard 328 as CrossRoads has suggested and PLEASE,

Can you please post a copy of your sketch, using code tags?
They are made with the </> icon in the reply Menu.
See section 7 http://forum.arduino.cc/index.php/topic,148850.0.html

Unless you post your code, we have no idea how you are configuring timers etc....

What resolution and range do you need with your stopwatch?

Thanks... Tom... :slight_smile: