Simple frequency to frequency converter?

[Joseph Davis]

Hi!

I'd like to construct a frequency to frequency converter for use in running GM 3" or 3.5" mass air flow meters on 90-94 DSM/Mitsubishis. There has been some discussion of doing this (by another route) on the dsm-ecu yahoogroups mailing list; apparently the GM MAF is compatible with the DSM ECU hardware, but it puts out a frequency four times greater than the stock DSM MAF. The proposed solution on dsm-ecu mailing list is to divide the GM MAF's frequency input by 4 on the code level, but without adequate dasm tools things aren't progressing quickly enough for my liking.

That, and I'm bored.

I don't see any reason why running a freq-to-volt converter into a volt-freq converter wouldn't work, but I'm wondering if there isn't a component out there that would do the job for me more simply. If I can get the signal scaled down to the correct range, it's simply a matter of plotting the MAF curve compared to the stock unit, kicking the ECU's MAF table a little, and verifying my work with wideband oxygen sensor + datalogs.

I've had a little past basic electronics in school, but it's been a while. What I'm angling for are hints, leads, harsh criticism, and datasheets. I go bang my head against them for a while with the help of my old textbooks on the shelf, then come back and ask stupid questions like a good little n00b.

Thanks!

 

[williB]

Hi!

I'd like to construct a frequency to frequency converter for use in running GM 3" or 3.5" mass air flow meters on 90-94 DSM/Mitsubishis. There has been some discussion of doing this (by another route) on the dsm-ecu yahoogroups mailing list; apparently the GM MAF is compatible with the DSM ECU hardware, but it puts out a frequency four times greater than the stock DSM MAF. The proposed solution on dsm-ecu mailing list is to divide the GM MAF's frequency input by 4 on the code level, but without adequate dasm tools things aren't progressing quickly enough for my liking.

That, and I'm bored.

I don't see any reason why running a freq-to-volt converter into a volt-freq converter wouldn't work, but I'm wondering if there isn't a component out there that would do the job for me more simply. If I can get the signal scaled down to the correct range, it's simply a matter of plotting the MAF curve compared to the stock unit, kicking the ECU's MAF table a little, and verifying my work with wideband oxygen sensor + datalogs.

I've had a little past basic electronics in school, but it's been a while. What I'm angling for are hints, leads, harsh criticism, and datasheets. I go bang my head against them for a while with the help of my old textbooks on the shelf, then come back and ask stupid questions like a good little n00b.

Thanks!

Joseph, what is the frequency of the GM MAF .. and is it a square wave?
also what is the voltage of the GM MAFs output ..

 

[Joseph Davis]

It's a digital/square wave signal, and peak output freq is 12 kHz but can be run close to 13 kHz before "clipping" occurs.

I'm ASSuming the voltage of the output is 5 volts, but do not know for sure - netsearching for that atm.

Thanks!

 

[williB]

if that is the case then you can easily divide the GM MAFs signal by 4 as it is comming out , and send it to the other unit..

 

[Joseph Davis]

Yup, I confirmed it. Later GM's use the Hitachi MAF meter, which outputs a 5 volt square wave signal @ perfect 50% duty.

You think the freq-volt and then volt-freq conversion idea I had would work just fine, or care to throw an old man a bone?

 

[williB]

why not just divide the signal by 4 ??
there would be no convertion problems..

 

[williB]

you could either use a programmable counter , or another counter with some glue logic to make it work..

 

[Joseph Davis]

I was about to post an obtuse question, because I'm an electronics tard. Instead, I re-read your post - freq + divide were terms you used. Reminded me of a voltage divider (within my current limited grasp) and provided nifty search terms. I now have a handful of example ciruits for frequency dividers, and a nice n00b how-to writeup bookmarked on my browser...

Thanks!

 

[williB]

try this ..
**broken link removed**

 

[williB]

sorry that chip was a bit of an overkill ..

 

[williB]

a simpler 74LS393 should do fine..
the 393 is a dual 4 bit binary counter..
just apply the signal to the clock input of one counter ..
take the QA output send that to the input of the second counter and take the second counters QA output .. and viola , your input signal is divided by 4..

 

[Sebi]

Dual D flip-flop - like 74C74 - also can do the job...

 

[Joseph Davis]

Groovy, I think I've got it.

https://www.homemadeturbo.com/forum/index.php?topic=42246.msg484799#msg484799

Already placed my digikey order. Toddling off now to hash out the MAF table I'd need.

Brute force induction of airmass is a wonderful thing...

 

[williB]

one more thing about the 393 you gotta tie the two clears to ground ..
because they will clear the counter if left floating..
EDIT :: as sebi said a dual d flip flop will also work ..
PS as i thought about it , one of the two available counters will work , just connect the signal to the clock input and select QB ..