Comments on: Digital RPM indicator

By: imsolidstate

imsolidstate — Thu, 31 Mar 2011 20:11:26 +0000

You can pretty much get the schematic by looking at the picture: Use one of the AVR’s ports to run the HD44780 controller in 4-bit mode, a connector for power, and a crystal if you aren’t using the onboard oscillator.

By: RS Hamlett

RS Hamlett — Thu, 24 Mar 2011 01:08:27 +0000

I’m wanting to build a 0 to 500 rpm counter for use on an 1894 steamboat.

Your Digital RPM indicator looks like what I’m wanting! Question; is it possible to get a circuit diagram of same?

By: Dave

Dave — Sat, 19 Sep 2009 14:16:10 +0000

It has been a fun project. I was excited when it first worked. I did not sleep for a couple weeks, just to add code. You are correct, the bulk of the complexity is in all the setup information. The code that runs the engine is about 4K bytes (ISRs and calculations), the total code is about 20K bytes.

I wish the best for you with your engineering degree. It is a excellent idea. With your present knowledge and interests you will a great student. You have an advantage by having interests and energy that will help steer your career.

By: imsolidstate

imsolidstate — Fri, 18 Sep 2009 18:33:37 +0000

Thanks Dave! I’m suitably impressed with your engine management system. I remember building an interface and hooking up my laptop to the ALDL connector on my ‘88 Blazer, I was totally overwhelmed by the complexity of all of the lookup tables and how it all worked together. I’m impressed you could build that yourself. Looks good!

By: Dave

Dave — Fri, 18 Sep 2009 17:17:17 +0000

Yes the flag is a global variable. I use CodeVision C compiler, it has bit variables. If your compiler does not support bits then a byte will do. Just set it to 1 for true, zero for false.

Your mechanical work is very nice. You have great potential. Your programming is good too. You may ask me for programming help if you need it.

I used a mega128 and built a working engine management system (fuel injection, ignition, idle speed and other controls).

You may find info here: http://my.att.net/p/s/community.dll?ep=16&ext=1&groupid=372867&ck=

By: imsolidstate

imsolidstate — Fri, 18 Sep 2009 02:14:04 +0000

Thanks for your comment. I originally tried to use the ICP since this is what it is intended for, but I couldn’t get it to work. I can’t remember why. So I did it the less efficient way to get it done. I’m still learning a lot about programming, and most of my stuff is trial and error.
I like the idea of using a flag and checking it from the main loop. When you say “flag” I assume you mean a global variable that you toggle. I’ll try that next time!

By: Dave

Dave — Fri, 18 Sep 2009 00:56:14 +0000

You might improve your code by reading about the timer1 input capture interrupt. You may have to use a different pin. The timer can be used free running (no need to reset to 0) and the elapsed time may be calculated by the difference, using the old stored in a “static” variable in the ISR. In the ISR also set a flag that a new Elapsed is available. In the main loop, use an “if” to check the flag, then do the division at that time, and clear the flag. By moving the division from the ISR improvement happens by minimizing the ISR code. This will help you in the future as you develop more complicated systems with many interrupts and calculations.

It is also possible to do this with the external interrupt, and not have to change the pin. The advantage of the input capture is it stores the timer value for you in an ICR.