myrio tachometer implementation

[cyotani]

I am building an automotive data logger using a myrio and am looking for the best way to get tachometer RPM data onto the myrio.

The output sinal I have is a 12V square wave. So if I were to using an analog read It would need some kind of voltage divider to scale it to about 5V. But can an anlog input have a high enough frequency to not miss any data. I believe at red line of the max frequency I will need to read is about 250Hz. So I would need to log at over 500 Hz and still have enough overhead for other functions I have in my code. 

I would guess a better way to do this would be using the fpga to find time between pulses to calculate rpm. But I am not sure how to wire this with the existing 12V tach signal. 

Another option would be a seperate magnetic or optical tach device that a mount on my engine which would be a last resort effort if I can not using the exisiting signal. 

Any suggestions to accomplish this would be greatly appreciated!  

[Danubio]

 Hey Cyotani,

I found this example that I thought could be useful to give yourself an idea about how could you get started with the application:

"Decoding Tachometer Signals Using CompactRIO/LabVIEW FPGA"
http://www.ni.com/example/27326/en/

Also here a good article to take in count some considerations about it:

"Decoding Tachometer Signals Using CompactRIO and LabVIEW FPGA"
http://www.ni.com/white-paper/3230/en/

Hope this can be helpful, 

Regards!

Daniel C.

[cyotani]

Thank you for the document.

So it looks like an analog read on the fpga is the best bet. Now I just need to scale the voltage down to under 5V. I'm guessing a resistve voltage divider will work for this?

[Danubio]

Yes, you can try that, just make sure the voltages and currents match the specs of the device.

Best regards,

Daniel C.

[cyotani]

okay, so I have sucesfully made minor changes to the analog fpga tach VI and hvae that code working and tested sucesfully on my car.

However, it seems like using that fpga code is not allowing me to use the pwm myrio functions. When I run the code with the fpga tach loop and a myrio pwm output I get an error -61202 at source "niLvFpga_Open_myRIO-1900.vi"

[cyotani]

Ignore my last comment. I found my answer in this thread and was able to get it to work.

http://forums.ni.com/t5/Academic-Hardware-Products-ELVIS/Using-more-than-4-quadrature-encoder-input-...

[vincent.ong@aiesec.net]

@cyotani

" When I run the code with the fpga tach loop and a myrio pwm output I get an error -61202 at source "niLvFpga_Open_myRIO-1900.vi"  "

I'm facing this problem in another situation, where i use SPI Open and Audio out Open (High Throughput)

Same type of error, can you elaborate on how did you solve your error code 61202 last time?

[ghadamf]

Hello All, 

I was hoping to get help with the problem that I'm facing which is "niLvfpga-Open_myRIO-1900.vi". For some reason when I switched from a computer to another one, I can not load my program because of aformentioned file missing!  I saw that there was a dicussion about the same problem in this thread but I couldn't arrive to the solution!

I will appreciate if you can help me with this.

Cheers,

Farhad