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can the pwm converter be used as a freq converter?

PostPosted: Wed Mar 11, 2015 9:21 am
by ashford
i have a car that has an 8000ppm speedo output but the speedo itself uses 30000ppm. the ms3 can convert it but the resolution is pretty bad it jumps roughtly 8%. at 70mph i have about 5 mph resolution ie 65-70-75.

i am just wondering if this unit can handle varying frequency not just pwm

Re: can the pwm converter be used as a freq converter?

PostPosted: Wed Mar 11, 2015 10:19 am
by jbelanger
It would handle a variable frequency but the conversion would have to be exactly a power of 2 for it to work, i.e., multiply the frequency by 2, 4, 8,... With 8000ppm and 30000ppm, it would probably not work very well. It would also cut off at low speed because it can't handle very low frequencies.

Jean

Re: can the pwm converter be used as a freq converter?

PostPosted: Wed Mar 11, 2015 12:01 pm
by ashford
i can do some adjustment in the ms3, its the frequency range/multiplier that the ms don't like, it appears dividers work better. i have done this in other cars with lower ppm output for ex a firebird had 48 tooth on the abs sensor(about 40000ppm) the speedo wants 4000ppm and it works fine.

an 8000ppm at 60 mph would be 133hz so 6mph would be 13hz. at what point would it "drop out"?

Re: can the pwm converter be used as a freq converter?

PostPosted: Wed Mar 11, 2015 12:22 pm
by jbelanger
It will stop registering frequency at about 8Hz. The timer will overflow and the unit will then assume the duty cycle is 0 so the output will be off; it could also be on if the input value is 5V for more than the timer period because that would correspond to 100% duty cycle. So I'm not sure what the behaviour will be below 8 Hz as it could translate into some multiple of the timer maximum period.

Jean