mx594m

iTrader: (1)

Description
The MAX9924–MAX9927 variable reluctance (VR or magnetic coil) sensor interface devices are ideal for position and speed sensing for automotive crankshafts, camshafts, transmission shafts, etc. These devices integrate a precision amplifier and comparator with selectable adaptive peak threshold and zero-crossing circuit blocks that generate robust output pulses even in the presence of substantial system noise or extremely weak VR signals.

BarbyCar

iTrader: (1)

Oh my!

Numerical value =/= Term

61* Fahrenheit = 16* Celcius
Fahrenheit and Celcius are both (names and) terms representing temperature, whereas 61 =/= 16.

Roy and Joe, you are in violent agreement, your only discord is the relative value of your adopted term.

(And the goldfish tasted like chicken)

mx594m

iTrader: (1)

actually this thread has been very helpful to me, I am thinking of moving to a 3.6 r/p and was wondering how I was going to correct the speedo display

this thread has lead me to believe miata transmissions have an internal VR sensor feeding a counting circuit driving the speedo display; if that is the case all I have to do is adjust the counting circuit to recalibrate the speedo display;

I am sure I will be corrected if this is wrong; in fact, if this is wrong, please do tell me how to recalibrate the speedometer after changing for a different differential ratio

chicken huh, LOL

shuiend

iTrader: (24)

The na's use a mechanical speed sensor that goes to the gauge cluster, and then the gauge cluster outputs an electrical signal that MS can read. The nb's have an electronic speed sensor.

To read the correct speed if you have a 3.6R&P you just need the correct speed sensor. I know they are out there, I am just not sure which one is which.

Oscar

iTrader: (2)

For reals? Where is this output located and in what form is it? Useful enough for the MS to use as a VSS input?

For the gears I found this: You can choose an M502-17-441 (19 tooth) gear or an M503- (20 tooth) gear, it depends on what wheel/tire combo you are using. With my 205/50R15 my speedometer was barely off compared to the GPS.

1011-17-442A - This is the sleeve/housing that will position the gear in the proper location to engage the gear within the transmission. If the sleeve that comes in a 5-speed transmission is used, the smaller 6-speed gear will be free-floating and will not engage. Thus, no readings.
M502-17-441 - This is the actual gear.
9922-20-214 - Spring Pin for holding the gear in the sleeve.
9958-60-8166 - Oil Seal for inside the sleeve.
1011-17-443 - O-Ring for the outside of the sleeve.

The above may or may not be actually useful

Joe Perez

iTrader: (8)

If this is for your '94, then as Oscar said, you have a mechanical speedo. The cable which plugs into the transmission has a little gadget with a plastic gear on the end, and you change that gear to recalibrate for different R&P ratios as Lars noted.


The sensor itself (a magnetic reed switch) is located inside the speedometer itself, and the leads are accessible on the backside of the printed circuit board inside the cluster.

In some NAs (1.6 cars without either cruise or an automatic transmission for sure, possible others), the wire which is supposed to leave the instrument cluster carrying this signal is absent. Later cars may or may not have the wire in place- you'll have to check.

Easiest way to find out is to pop the hood over the instrument cluster and look for a grn/red wire at terminal 2F:



If you don't have the wire, you can run one directly to the terminal on the back of the speedo. I posted a picture of this years ago in the Emanage forum, too lazy to look for it.


The switch is a closure to ground, so you'll need a pullup if you have an early car with no A/T or cruise. Test the wire first- it may already have voltage on it (test it while moving slowly, so ensure that you cycle the switch on and off) in which case no pullup is required.

mx594m

iTrader: (1)

no I haven't searched [yet] cause I am not ready to pull the trigger on the r/p swap
[and I did not even know about a sub-forum called emanage]

yes my trans is the stock 94, and since my car is an M, it does have cruise

thanks for the pin out, most helpful to us males with defective color preception

Joe Perez

iTrader: (8)

Heh, a green wire with a red stripe. I didn't even think of that.

shuiend

iTrader: (24)

I will check out my 94's wiring tonight to verify what joe posted. VSS has been working well enough in my car, just has a problem with calculating the correct gear for lower ones.

Oscar

iTrader: (2)

So the 94 cluster actually puts out a usable VSS for the MS? Not gonna lie, I'm pretty hard right now.

Joe Perez

iTrader: (8)

Huh?

The VSS signal, be it from an NB-style sensor or an NA-style speedometer, is taken from the tailshaft of the transmission (after the main gearing) and is thus accurate regardless of what gear you are in. It would work for a car rolling down a hill in neutral with the engine off.



Yes. I had this wired to the EMU in my '92 many years ago. It's how I know I was doing precisely 104 MPH when the cop pulled me over in a 55 MPH zone.

shuiend

iTrader: (24)

My MS reads the speed fine, it just does not always compute what gear the car is in correctly, esp at the lower gears. From my understanding with MS3 you put in how many gears you have and the ratios. It then determines which gear you are in based on your speed and rpms. For some reason in the lower gears it tends to read about a gear below what I will really be in. It might be slightly my fault since I generally start in 2nd with my 6speed. I just know I have done pulls from 2k rpms to redline in 4th gear and when I look in my logs it shows me being in 3rd gear for most of the run then randomly switches near the top end.

Joe Perez

iTrader: (8)

Aaah, gotcha.

Oscar

iTrader: (2)

Awesome, thanks Joe!

WestfieldMX5

Thanks for the info guys. So we have a VR sensor that outputs a 8200 ppm AC signal.
To convert this to a 0-5V DC signal for the MS, I can copy the stock VR circuit from the V3.0 board, a LM1815 based circuit or the Maxim 9924 based circuit (but those are too difficult to use). Will try to get the LM1815 circuit in the proto area.

My S2000 cluster expects 156K, so I'll first have to multiply the input frequency by 19, unless the MS output can do this.

cordycord

iTrader: (2)

Most speedometers are square wave and read off the leading edge of the square. The pulse is generated by a reluctor as a permanent magnet passes. As Joe mentioned earlier in the post, the easiest way to check the pulses is to check the reading when the car is moving. A dyno can be a helpful tool for this as well.

hustler

iTrader: (6)

Have you ever datalogged this?

cordycord

iTrader: (2)

Only on motorcycles, sorry. I was looking for a picture of the mini-oscilliscope I used, but I must not have kept the pictures. However, I do have some reference numbers for a Honda:

180mph = 3.02 KHz
119mph = 2.00 KHz
59mph = 1.00 KHz
3mph = 50 Hz

The minimum voltage required to trigger the reluctor was 3.85V p+p, and normally ran on 5V.

Interesting; the odometer was clocking the miles while I tested the speedometer readings. Also, since standard speedometers don't show tenths of a mile, a set mph on the speedometer would be shown within a range of Hz readings. Hope this helps.

WestfieldMX5

Turns out the signal is 4800ppm, not 8200ppm and the S2000 cluster expects 156K thus 32.5 times faster.
I'm using a 32 multiplier which is close enough. The stock speedo reads a bit high anyway so it'll be spot on. If I get it working that is.

mx594m

iTrader: (1)

What was the rear axle ratio of the vehicle that the transmission is/was in?