fluke

The spec sheet quotes the maximum current for you to design a power supply that can deliver at least that much. ICs don't need external current limiting. It's probably easiest if you think of CMOS working on voltage, not current. Power supplies always supply voltage, not current. An LM317 is a adjustable voltage regulator, but you can configure it to adjust the voltage so the current is constant by having it sense the voltage across a small resistor. When you have resistors in series, they have the same current and "use up" all the voltage. The voltage across each one is proportional to it's resistance, ie V=IR. So when you have 5V to an IC and put a resistor in series, the IC no longer gets 5V. More information can be found if you read up about Kirchhoff's Laws

For almost everything except LEDs, the maximum supply current is the most it will draw. If you want to protect the device from drawing too much current (due to a fault such as a short circuit), use a fuse or a polyswitch. You'd usually only use 1 protection device per regulator. LEDs don't limit the current they draw and will overheat and damage themselves if not regulated. Since most LEDs have a voltage drop of less than 5V, you use a resistor to drop the extra voltage and limit the current. If you really want a constant current regulator, use a LM317.

I do intend on building one, so i'll wiki my design as soon as i do. Now i just have to figure out a user interface design for a Midibox FM involving 48 led/buttons, a PalmPilot and a few encoders...

I don't think it's uncouth. Considering where you are, rather than cash, you should be offering hard to find knobs or sacks of dual-colour LEDs. :)

A slightly off topic question, but shouldn't you have a transistor in the DEFAULT_SRM_DOUT_CATHODES_R D0-D3? You've got it sinking current from 16 LEDs per pin and i thought a 74HC595 could only sink 20mA per pin. My calculations say that if all the LEDs are on, you'll need to sink around 250mA per pin.

Now we just need someone selling 238 YAC512 chips and we'll be set. ;D

What's the reasoning for using a separate regulator? Wouldn't they be sharing a ground line anyways and thus get the same noise?

My wife thought of a very cool case idea the MIDIBox FM i'm planning on building. However the best mounting position for the LCD in it is a 45mm diameter hole. Does anyone know where i can find a round or square LCD of at least 45mm diameter but not much more? A PalmPilot would work, but i'd rather not put one in as it would be awkward to install software on it as i won't be able to easier remove it. Then again, that may be the cheapest option.

It's probably not possible, the driver API changed many times between Windows 3.1 and XP. Give it a go though and see what happens. What i have been thinking of is to use DOSBox (http://dosbox.sourceforge.net/) to play games with good patch sets, dump the OPL3 data and extract the patches from that. You should be able to get Windows 3.1 to run under DOSBox.

A SoundBlaster Pro2 or 16 card or clone will have both chips for a 2 channel MidiBox FM (a second DAC is necessary for all 4 channels). Try your local computer recycling store. You can find a list of suitable cards in the wiki: http://www.midibox.org/dokuwiki/doku.php?id=soundcards_with_ymf262_and_or_yac512_chips

I had replied to this before, but that was on Friday the 13th. So here it is again from memory: Indirection basically means pointers, eg: int a; // direct int *b; // indirect int **c; // 2 levels of indirection Both errors were with pedal_group_stored_pin, it's definition should be: unsigned char pedal_group_stored_pin = ... But if it's: unsigned char *pedal_group_stored_pin = ... Then that's the source of your error.

I'm just guessing, but both errors involve references to pedal_group_stored_pin. So i'd suggest looking for its definition and seeing if it really is an unsigned char.

I found an oscillator on an Aztech soundcard. Have a look for 4 legged metal cans with 14.318 written on them. Futurlec have them for US$1.20, with no minimum order and freight to Europe of only US$4. http://futurlec.com/ICCrystalsOscillators.shtml

That would most likely be an ASIC with an OPL3 core inside. The DAC could be inside, outside or it could use a non-YAC512 DAC.

Thanks heaps Thorsten

How did i miss that? ??? Obviously a sign i need more sleep. ;)

I'm wanting to build a MidiBox FM and i can find most of the parts here in NZ for the OPL3 module (the other modules i can get as kits from Smash TV), but i can't find a 14.318 MHz TTL Oscillator. One of my sound cards has something that looks like it might be it: It's got 4 legs, one's connected to the ground plane on the back, the other 3 are through to the top (i assume). How do i tell if it is a TTL Oscillator instead of just a 4 legged crystal? How do i test it still goes once i desolder it?

Here's my sound card for comparison: Unlike AndAway's, it doesn't have a YMF262, though it does have a YAC512 (bottom right, chip to the left of the AZTECH one).

Hmmm, that's the same FCC ID as my Aztech card and it doesn't have a YMF-262 on it, at least that i can find. Could you post a photo of the card?

How much are the 4x20 displays and do you take NZ money?

The YM3812 was on the Adlib and original Sound Blaster. The first version of the Sound Blaster Pro had 2 (for stereo), so from that list above, you'd want: CT1320 Sound Blaster 1.0 / 1.5 CT1350 Sound Blaster 2.0 CT1330 Sound Blaster Pro 1 Any 8-bit ISA (with only the larger one of the two "goldfinger" connectors) Sound Blaster clone card should have them. We did have an Aztech BX-(something) that had them.

It would be useful even beyond MIDI, i could use it to control my Linux server. I've started writing it, currently you can create buttons and labels and when you click on the buttons they display a hex string. (PalmOS <3.5 doesn't have functions for dynamic UI creation, so i'm doing everything manually.) I need to rewrite it with a proper parser, instead of my hackish string splitting code. I can send you a copy of what i have now, or give me a week or so to rewrite it.

There are ports of J2ME to PalmOS, but they don't have access to the serial port. JSynthLib won't run on J2ME anyways and the entire interface would need reworking for the small screen. How about a system where locations of buttons, sliders, "LCD" display, etc and the MIDI command to send are defined in a Memo (or text file linked into the application)?

So that's 2 votes for a PalmOS port of JSynthLib? ;)

A rotary encoder isn't the same thing as a linear slider though, it doesn't stop at each end. It's really two buttons, one for each direction. A pair of buttons doesn't have the same metaphore as a knob on screen though. Hence my request for someone else to do the UI design. ;) The knob could be made smaller, i was just using all the left over space.