voltage threshold for interrupts

The exact levels at which interrupt inputs trigger depends on the technology of the parts used. If, as you describe, you have specific needs that differ from your part's characteristic, you could provide additional circuitry, perhaps using op-amps, to process the input.

The major problem with your specification is that there is little "dead band" between the high and low states, and your system will suffer due to insufficient noise immunity.

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          Michael Kesti            |  "And like, one and one don't make
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Interrupts have nothing to do with it. You are interested in logic levels. Receivers for such low level swings will normally be based on long-tailed pairs, op-amps, etc. Your best bet for cheap available ICs for the range might be RS485 receivers, which will convert to the usual logic levels.

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Maybe what he's looking for is a comparator between the interrupt pin and his source. I can imagine some sort of opto or inductive sensor that he wants to derive an interrupt from.

I cannot use amplifiers. The circuit I am developing should use a low power as possible and amplifiers or other preprocessing units usually consume power.

I certainly agree. With help from google, I find some low-voltage microcontrollers have a "dead band" of about 0.9V but it is still to large for my device. Are there any microprocessors or interrupt handler circuit that can accept a high/low of 0.5V/0.1V?

Thanks!

lin

I don't know of *any* logic that works with IO voltages below 1 volt. You can get micropower analog components. What you are trying to do is not a normal digital function and should not be considered as such. Find a comparator with a low enough power consumption and work with that. Some even have a reference built in.

If you want precise voltage thresholds like that, I think you'll need to use an analog comparator to measure the voltage, with the comparator's output generating a logic level signal to be used for the processor's interrupt input.

Digital inputs to microcontrollers (or digital ICs) are not intended for precision voltage measurements.

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This depends on what you consider low power. For example, the TLV370x family of comparators consumes around 600 nA/channel. Is this acceptable? (Note that the speed is rather moderate, around 40 us.) There are some comparators with even lower quiescent current, but they tend to have an open-drain output which then consumes some power.

Another possibility would be to use the internal comparator of a microcontroller. It consumes probably a lot more, but you can switch it on only once in a while to check if something has happened in the inputs, in case your speed requirements allow this.

Of course, your total power consumption will depend on how you make the reference voltage for the comparator. You'll need to use megaohm resistances in any case.

You could use an amplifier to amplify your input signals to acceptable levels. However, linear amplifiers provide a worse power-to-speed ratio than comparators.

- Ville

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Ville Voipio, Dr.Tech., M.Sc. (EE)

There are uC available that include very low power Comparitors, that can drive the INTERRUPT logic. These allow you to define your own voltage threshold levels. Look at the

families, and also the Philips P89LPC9xx families. IIRC, the Cygnal ones can run < 1uA of comparitor Icc adder.

-jg