Square wave frequency input

[2002tiiguy]

If i have a 5V square wave that i want to read the frequency of this square wave. can i configure the ms2 to read that frequency? if so, how? frequency is in the range of 0-300hz

[slow_hemi6]

Might be possible with a lm2917 frequency to voltage converter and connection to adc6 or adc7. What are you trying to monitor?

[2002tiiguy]

vss out of the back of the speedometer on my 89 e30, supposedly the signal coming out of the speedometer is a square wave. since the flex fuel sensor is also read based on frequency i should be able to read the speed signal

[slow_hemi6]

Specific code would need to be written for that and my guess is it would be this or flex but not both. MS2 only has so many timer resources available. I've noticed there is not much enthusiasm for new ms2extra code/features but good luck with it.

[nathaninwa]

I'm not sure ms2 can do anything with the signal. Can a generic speedometer be created in TS to at least show speed maybe?

[slow_hemi6]

Set up the way I said you can configure tuner studio to display with a custom gauge, you can datalog with a custom channel, you can use programmable outputs with raw adc values from adc6 or adc7.

[2002tiiguy]

ah, so adc6 and 7 are the spare adc's, i was really confused

[2002tiiguy]

for the input values on the custom channel, what am i entering? can i just put the 0 and 300 hz in for point 1 and 2, or do i need to do something different?

[slow_hemi6]

Adc can only respond to voltage levels. They can not deal with a frequency. In order for a micro controller to deal with a frequency it must use a timer to do a compare of 1ON and 1OFF period to the time elapsed on the timer. This is mostly accomplished with an inbuilt timer module which saves greatly on processor resources. The timer module is already heavily utilized by MS2extra. The timer module also only works with certain input pins.

[grom_e30]

the only way to achieve this is with a frequency to voltage converter so 0mph would be 0v and your max speed would be 5v then read the voltage with the megasquirt adc and you could calculate the speed based on the voltage the ecu is reading.

[2002tiiguy]

so how does it read the flex fuel sensor?

[jsmcortina]

so how does it read the flex fuel sensor?

It is very low frequency and it is sampled by polling the pin.

James

[2002tiiguy]

gotya, guess 300hz is just a little too high