MSgpio.com read only forums (Jan.15,2018)

Hi Lance,
I'm using GPIO as stand-alone and not using CAN but want to read engine rpm.
Is it necessary to add all the componets (transistors) to the "VR3" input section when using the GPIO to read Engine RPM from a Tach signal?
My tach signal is "square wave" +12v.
Thanks for your advice on the circuit.
Rob

Rob,

Finally found your post (it was hiding in another thread with the recent forum issues!)

As we discussed in PMs (earlier today), if you already have a nice square wave as an tach input, you don't need the full VRx circuit. You just need to cut the amplitude down to 5V. You can do this with a couple of resistors to form a voltage divider. Then add a 5.6 Volt Zener diode for extra protection. This might be needed in case the signal is too large, or especially if there is large but brief voltage spikes induced in the wire from the engine to the controller, possibly by a coil firing nearby.

Lance.

Lance,

What would this circuit look like in VR3? Would this work for the speedometer input? My thoughts: take the signal off the ABS signal wire from the VSSB on my 92 Chev that I would assume would be a 12v square signal at 128,000 pulses/mile. I would use a second VSSB from salvage yard to avoid affecting any of the ABS operation. I can not seem to get a clean signal into the MegaShift. I have tried different resistors from 47K to 300K as you suggested with no luck and was thinking that the VSSB would filter the signal enough to be used by the MegaShift. Let me know if you think this would work.

Silverado

Silverado,

This is how a voltage divider works: http://en.wikipedia.org/wiki/Voltage_divider Vin is the signal from one wire of the sensor, the other wire is grounded. Then you would put a 5.6 Volt Zener diode with the banded end at Vout (in the diagram at that link), and the other end of the Zener diode would be grounded.

But if this was mine, I would just build the full VR circuit as normal - it will work fine with your 0-12V signal. If it doesn't something is wrong with the way the circuit is built.

However, I am also working on a small adapter board right now. This will have an advanced VR chip (with differential input and adaptive peak threshold) on it for two VR sensor inputs (converting them to clean square wave outputs that can be fed directly to the processor pins), and also have a 1 Amp high side driver circuit for the pressure control solenoid (making the pressure control much less sensitive to supply voltage variations). It will be at least a month before this is ready, though.

Lance.

Lance,

Great, I am interested in this adapter. Would this adapter contain a chip similar to the MAX9924?

Silverado

Silverado,

Yes, it will have the MAX9926, so it will be able to handle two VR/Hall sensors (for VSS and ISS or a tach signal). The chip will be soldered to the board (it is an SMT device) but the remaining components (there aren't a lot of them) will be DIY.

The 1 Amp constant current circuit will use a couple of transistors and resistors to give a nominal output of 1.06 Amps. GM uses a similar circuit for line pressure control on the 4L60E and 4L80E, that's why both the high and low side of the pressure control solenoid are brought out to the ECU.

The design is finished and the behavior looks good in LTSpice. The board is nearly laid out now. I need to finish this, check it over, and send it out for production. Then I need to write a BOM and assembly instructions. If all goes well, I hope to have this done in 6 weeks or so (maybe sooner).

Lance.