> I don't know what "power decoupling" is http://en.wikipedia.org/wiki/Decoupling_capacitor See Transient Load Decoupling section http://www.seattlerobotics.org/encoder/jun97/basics.html Mention of it in two of many Microchip documents http://ww1.microchip.com/downloads/en/DeviceDoc/power.pdf http://ww1.microchip.com/downloads/en/AppNotes/00763b.pdf Most people would probably put a 10uF and 0.1uF close to the micro, 0.1uF ceramics around the circuit and possibly a bulk electrolytic too, perhaps 100uF or 470uF, something like that > Somebody mentioned this chip to me already. I looked it up and > go its datasheet but I couldn't make any sense of it. Haven't a clue > what it does. Well, an HC595, like other serial-parallel convertors, turns serial data into parallel data. This means that you feed it a clock and an 8-bit byte of data into two pins, and the contents of that data byte appear on the output pins in parallel format. Look at the timing diagrams carefully The HC164 is another shift register. This circuit drives 28 LEDs with just 2 pins (apologies for white-on-black images) http://home.clear.net.nz/pages/joecolquitt/2wireled.gif 448 LEDs with a 16F628 http://home.clear.net.nz/pages/joecolquitt/message.html > It's a piezo speaker! I'm not the greatest artist :-P A piezo often has the same schematic symbol as a crystal You can save 4 pins by multiplexing the buttons with diodes, as per http://home.clear.net.nz/pages/joecolquitt/chaser.gif Note that the logic is the reverse polarity of your pulled-up-and- grounded inputs. For a 7-to-3 multiplex, eg no buttons pressed = 000, button1 pressed = 001, button2 pressed = 010 etc up to = 111 for button7 > At the moment I'm think of going from a 9 V square battery into > an LM7805. I'll get around to that in due course Very wasteful, and particularly so because the whole circuit is running on 5V, AFAICT. If you have to use 9V, then at least run the LEDs on the unregulated 9V, rather than the regulated 5V. For parts that actually need 5V, a 78L05 or LDO would. Although given the number of LEDs (56 by my count), any reasonably-portable battery-based power supply you choose won't last long. It's quite possible that you might be drawing an average of 250mA. You will, of course, be very popular at the battery shop -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist