uROEFI

[m3ltd0wn]

What do you think about this hall circuit?
It is based on a circuit that I've found in the hardware forums, used in miata ECUs, I've changed the second input so it can support High to Low Hall sensors.
I know that most common hall sensors used are Low to High, VW used them on ABF engines and are widely avaible and cheap, and with few modifications they can fit on BMW as well, they have the same mounting holes and same distance from the trigger wheel to the sensor, but in case I stumble across High to Low sensors I am able to switch a jumper and the problem is solved.

Let me know what you think.

[Fred]

You don't need two variants.

FreeEMS input topology for RPM/position sensors is such that for a give OEM setup with OEM sensors the signals, whatever they are, should be inverted before hitting the CPU. This has a lot of benefits which I won't explain here, however as long as high on input means low on output, and vice versa, it'll work.

How much hysteresis does this setup have? Getting ICs with good hysteresis isn't easy. Look at Dan's RB ECU for a possibly simpler approach with an IC with moderate hysteresis.

Fred.

[Fred]

Re earlier post about "active high circuit" I don't understand why you're using a FET driver IC for an input buffer, and also how you think you can get away with no protection on those inputs.

[m3ltd0wn]

If you are referring to max9926 IC for the rpm input, well that is out of the question, I did not find any supplier in my country that can provide that IC, I can use the LM1815 IC or opamps to do the job, TL082 jfet opamp datasheet http://www.farnell.com/datasheets/127138.pdf that is used in the schematic above, and in the schematic found on hardware forums, that is based on OEM miata ecu ...

As for the fets I was tired and totally forgot about the protection on their inputs, they are rated to 18v input voltage, I'll add a resistor to lower the amps as per their datasheet, I also could use an active low input using 2 diodes and one resistor feed from +5v analog rail, thanks for opening my eyes

[m3ltd0wn]

I've seen the Dan's RB25DET ecu schematics, he is using the MC74HC14AN hex inverter with schmitt trigger, interesting choice and good noise protection, but from what I'm reading on the datasheet it only supports input voltage of +5v +/-0.5v, it is ok with modern hall sensors because they work with +5v or +12v, but older versions I think won't work with +5v supply voltage if they are designed for +12v supply, I'm referring here to those distributor sensors from old bmw and vw, m10/m20 engine codes(bmw, some of them have vr sensors) and KR,GX,DX engine codes from VW.
On some VWs, the sensor is fed from the ignition module with +12v, models that have K-Jetronic injection system.

[Fred]

If you clamp and current limit it could be 5v or 25v and the ECU would work either way. Not optimally, but nothing would be for the 25V case anyway.

As for MAX992X ICs, they're not available in any country/available equally in every country via import. I didn't just walk into a shop and buy mine :-p

Fred.

[m3ltd0wn]

Hello Fred,

Yes I know, I couldn't find MAX992X on Farnell, and nor on TME, they are the main suppliers in my country, if I was to order the IC from abroad I think the costs will be much higher.

Meanwhile, I've modified the Hall input circuit and active high inputs for launch control and table shift functions.

LE: found an old distributor in the shed, it was fed with +12v from the OEM loom, I've connected it to a +5v source and it worked, so I've eliminated the jumpers that would select the input voltage to the Hall sensor, but I'm keeping the non inverting and Inverting jumpers just in case

[Fred]

What you have in a car is a loom and in this loom you have 12V which is native and feedable to anything that needs it via relays and fuses. This takes care of your 12V needs. What you have in an ECU is one or more 5V outputs, these can supply TPS, MAP, MAF, Hall, and other trivial low-current devices where necessary. I can't think of a good reason to ever supply constant 12V through the ECU. Switched 12V for various things, OK, but constant, no.

Again, your diagram still contains an invert option for the input. This is not OK in terms of "standards compliance" and should be removed with one inversion between source and CPU the standard.

Re max, it's the only good option for VR IMO. You can get small quantities as samples. Larger quantities spread the taxation and shipping costs over the number to make each one not so bad.

Fred.

[m3ltd0wn]

Yes you are right, +12v switched is to power up the ECU, Launch input switch is on the clutch pedal, and it is feeded with +12v from the car's electric loom, it is normally open switch and only the clutch is pressed then it feeds +12v to the active high circuit, the same applies to the Table switching circuit, only that there is a switch in the console.
The other +12v rail is needed in case older VAG COP revisions are used, and they are triggered by +12v, other revisions are +5V triggered, and finally I have ground switching for old ignition modules (old but good in harsh environments, I've seen BMW COPs fail, VAG COPs fail... but yet I have to see a Bosch 139 module fail ).
And for tacho output I have a jumper to switch the voltage, older cars use +12v feed to tacho, new ones +5v, so I can choose between those .

I'll leave the schematics like they are now, and see what layout I will use for the PCB, I've seen cinch enclosures for cheap, and I will use OEM connectors, I'll just desolder from the old ECUs and solder them to this one, using the same wire configuration for the vital parts, and ditch the rest or convert it to be used as outputs to different functions , a rally car must be light lots of wires means lots of copper = weight

[Fred]

You've misunderstood (or I have!). I'm only talking about your "5V or 12V for hall sensors" situation.