Filtering Tacho signal to 5v pulses

[punkture]

takai; i have a circuit diagram that should help;

[punkture]

Freaking firefox double post

[oldcorollas]

Also, getting the opto is a pain. Its either Farnell or RS components, and ill almost be paying more for postage than an entirely new Arduino..

any of the MS kiddies should have a spare opto..

[punkture]

if its just to filter to 5v pulses, the tacho circuit i posted does just that =) elec engineer did it for me. hope it helps mate

[o_man_ra23]

Simple comparator circuit would do the trick. Surely Jaycar stocks comparators. At a pinch an op amp like the LM358 previously mentioned with a huge gain will give you a nice square signal out, but not quite as clean as the comparator.

The problem with the zener is that it needs to dissipate energy to keep the voltage down. The greater the voltage difference and the bigger the load, then the more heat it dissipates. The comparator doesn't do this, as the input is very high impedance, and is only used as a signal to drive the output which will run off the voltage rails you give it (ie 0-5V)

[wilbo666]

First thing to check is if IGT is 5V on 2JZGE, it might be Pretty sure IGTs are on xJZGTEs.

Second, it's not like we are taking the -VE of the coil here, takai is trying to take the signal that goes to the igniter

Just to throw some more fuel on the fire ...

Atmels have pretty good ESD protection in my experience, and to be honest I think you could get away with a straight voltage divider (Size the resistors for say a max of 16V input, and then check to see the Atmel datasheet for you micro to see what the input voltage will be before and after the Voltage divider that meets the voltage level for the micro guaranteed input high - see if this is suitable, then you can always throw the zener in if you fell like it also...).

<more fuel>
In fact I reckon you could do it with just a series limiting resistor (no voltage divider), there is an Atmel app note that states you can exceed Vcc at a GPIO pin and take advantage of the internal protection diodes to the rails. It recommends limiting the maximum current thought the internal protection diode to 1mA.

AVR182: Zero Cross Detector on tinyAVR and megaAVR devices




Edit: Also the switching speeds we talking about are really quite slow, I wouldn't be too concerned about the slew time of an NPN etc

Cheers
Wilbo

[takai]

Hm, my oscilloscope is busted, and the multimeter isnt fast enough to sample the signal. Looks like its 5v though.

Reading up on the AVR documentation the worst that will happen is that ill kill an IO pin, which i have 12 of and ill only be using a maximum of 3.