Hardware interrupts, extend no. of outputs

Hey there,

I have one of my external hardware interrupts set up, and it has one funny little problem - when I even touch the wire of the switch on the breadboard, it triggers the interrupt as well. Any ideas to prevent such over-sensitivity?

Also, what's the best way to extend a microcontroller's number of outputs? I've read out that the D-flip-flops could do so.

Assuming a switched ground.
Pull ups.. If you are relying on the internal pull up of the microcontroller you are using (if your uC has one, you haven't mentioned what it is), these are called weak pullups for a reason and maybe inadequate for your breadboard setup.

Buy an I/O expander. They are cheap. Something like this:
Parts: 8bit IO Expander (PCF8574) - Hack a Day

If its only outputs i would also recommend a shift register... which is serial aka easier to use and also cascade-able which means you can line 2 + together to make a multiple 8 bit outputs.... (get it with a latch)

74xx595..
xx can be LS, HC, AC etc... for more info on the xx part check:

7400 series - Wikipedia, the free encyclopedia

I've got the hardware interrupts done finally with the pull-ups.

Next thing is the 74LS174N shift registers I've them on my hand.

I've wired the inputs/outputs of the shift register to a bunch of LEDs, and however, all of the LEDs are lit up only and refuses to budge when I tested it with some clock pulses. Any good guides to wiring up these?

What I do to expand the ports is to use 4 output ports to control a 74hc138 decoder and it will select each of 74HC373 data latches. Now you can have a total of 64 outputs off of 4 processor outputs. So you will run your data bus, say 8 data output ports to the D inputs of all the '373s and you can latch them up individually with unique data for each one by selecting one at a time through the '138 "one of eight decoder" chip by attaching Y0 through Y7 to "OC" output control of each '373.

Here ya go

That's a pretty "resource intensive" solution Varmint (using 12 PIC pins).

Here's an example of another solution, courtesy of guru' Roman Black's Shift1 System for 1-wire Shift Registers, that uses a single pin and relatively inexpensive 8-bit serial-to-parallel latch ICs.

Happy Holidays. Mike