DammitBeavis

I'm looking for a simple circuit to read my ABS sensors without interfering with the operation of my ABS system. I need to convert the AC from the mag sensors into a 5v square wave like a hall effect sensor would put out. It appears that I need a reluctor interface with a high impedence floating input (neither input grounded). The megasquirt kept coming up as I was searching for a circuit. It looks like it can be built with a VR reluctor interface for reading cam/crank mag sensors? Does this circuit have a floating input? If so, can it be lifted from a diagram so I can build one?

Joe Perez

iTrader: (8)

MAX9924.

I used this chip in my new crankwheel decoder. It's awesome and also has a differential input. Build the circuit as per the mode A2 reference schematic in the datasheet, and it's just plug-n-play.

DammitBeavis

Well ****, Amazing! Thanks!
What's the best way to prototype with those surface mount components. I've never messed with components that wouldn't stick into a breadboard.

Joe Perez

iTrader: (8)

Here's how I did mine:



The little adapter board was just a few dollars, and if you're not comfortable doing SMC, they will even mount your chip for you.

Source thread: https://www.miataturbo.net/megasquirt-18/max9924-47243/



It's a damn shame they didn't use this chip on the new MS3X board; that would have been a fabulously simple, reliable, highly versatile way to go.

Or did they?

We'll never know, since the schematic is a closely-guarded secret inaccessible to us mere mortals.

DammitBeavis

That's just in-*******-credible. Everything I need from a pair of 9926 chips for $5. Then $8 for two of those breakout boards. The ($8 ?) assembly charge for one of those boards sounds like a great alternative to screwing around for 2 hours with an iron. I'll have less than $40 invested in a 4-channel reluctor interface!

Looking at your scope captures, I could probably use 100K resistors on the input side and still get a reliable output.

What size caps are you using to filter the power supply?

Thanks again!

Joe Perez

iTrader: (8)

The ones they specify in the documentation. 10nf, .1uf, and 1uf. I also tossed in a 10uf, just out of habit. The small ones I soldered directly to the backside of the carrier.

WestfieldMX5

A propos, c'est le poulet et la poule

DammitBeavis

FYI, Proto-Advantage quoted me $11.99 per adapter with assembly, and $2.97ea+$10 shipping for the MAX9926 chips.

So 4-channels worth of VR Interfaces on DIP adapters and ready to mount for $39.92 + Shipping!

They recommended that I sample the chips and ship direct to them to save a few bucks.

Edit: Shipping was free from Maxim to Proto for the samples, So the TOTAL cost for the first two was $23.98 + $4.00 Shipping.

Joe Perez

iTrader: (8)

Sounds good. The 9924/9926 really are incredible devices. If you look through the other thread I linked do, there are scope traces where you can see the chip pulling signals out of noise that renders them virtually invisible and producing reliable outputs every time. Just amazing.


One word of advice: when I got mine, I sampled them as well, and they took half of forever to get here. Maybe now that there's stock in the US it'll be different.


So, the big question: What the hell are you building?

DammitBeavis

I need to feed the signals from my ABS sensors into my ECU to setup traction control.

DammitBeavis

I really only need 3 channels. One for each front wheel, then driveshaft speed for the driven wheels. The ECU can use Min, Max, or Average the speed of the two front wheels for accurate readings in turns. I'm putting in a **** to select off, dry, or wet tables. In each table I can define per-gear slip limits and how aggressively I want it to cut power. It should be fun to play with.

Joe Perez

iTrader: (8)

Jeremy Clarkson would approve of this. Just make sure that the "off" position has some bizarre, incomprehensible acronym such as "CST".

DammitBeavis

I prefer random colors. Right now my Launch control switch is white, ALS is yellow, fan override is black, and logger is red. If I label it at all, I think maybe green/blue/grey dots? It's even funnier since I'm red/green colorblind.

DammitBeavis

OK, since that last problem was so easy to solve...... so I'll ask another thats a bit more difficult.
Is there a chip that will take two pulsed inputs, and average them into one pulsed input? I guess it would need 2 frequency counters, add them together, divide them by 2, and generate a square wave at the target frequency.

Joe Perez

iTrader: (8)

Yes. It's called a microcontroller.

(An FPGA would probably also work.)

DammitBeavis

I was looking at an Arduino. With a proper microprocessor doing some math, I could integrate a yaw and accelerometer sensor (I already have a BOSCH sensor box from an STI DCCD system) to get accurate relative wheelspeed in a turn. Then I could feed the ECU an 'ideal' slip ratio.

DammitBeavis

The assembled boards shipped today. That was fast! They recieved the sample chips and assembled the boards 4 days after ordering.