lylehaze

Well, I hope "Design Concepts" will work, I couldn't find "Stupid Questions", so I'll try here. I have hand-wired a DINX1 to connect a single encoder and a single pushbutton. No problems there, but I need to figure out whether I'll be connecting to J9 or J6 of the core. The application was written by Pilo, to control a PGA4311 chip. I have his source here, but I don't know where to look in the code to see which connector is used for the encoder. I suppose I can try both, but if anyone knows a more definite way to tell, I'd love to know it. Thanks, Lyle Hazelwood

Pilo, Thank You. I have your code, and I look forward to getting into it as soon as the hardware is finished. I worked most of yesterday on the power supply. It is working and mounted in the case. I have also mounted the core and display. Today I think I'll try making the summing amp for the mixer, and maybe a few stereo input modules. I doubt if I'll get any PGAs wired up today, but maybe next week. It is coming along very slowly, but there is some progress. Thanks for your help, LyleHaze

I have not looked too deeply into the SID's, but a quick glance shows that some of them have a matrix of LEDs for display. I can't (quickly) find a schematic, so I'll have to wing it here.. Assuming an 8X8 matrix, We'll have each row connected to eight LED Anodes,we'll call those 8 Group A, and each column connected to eight LED Cathodes, group B. Let's say you want the first Row with ON OFF ON OFF ON OFF ON OFF, a simple 4 on, 4 off pattern. So you set up group B with the on-off pattern you want, then enable them by turning on the driver for the first Row. At this moment, only the first row has LEDs lit, and those are alternatinn ON and OFF as you arranged it. Now look at your current draw. Four of the group B outputs are sinking enough current for one LED, the other four are not. But the single ROW driver that is enabled must source enough current for all four of those LEDs. Under "worst case" it might be eight at a time. I would suggest that the PIC outputs will not source or sink enough current to drive eight LEDs on a single pin. Assuming 20 ma per LED, you may need to source 160 ma under the "brightest" conditions. This is not an issue if you limit your displays to only a single LED in each ROW or Column, but when I design circuits, I like to leave my options open if I can. I have not yet seen the schematic for these matrix displays, so I can't say for sure what is doing the driving. I may well be wrong, but I hope at least the explanation makes some sense. LyleHaze

The last post you showed was for 64 Inputs in a matrix. It works like this: Set all outputs to HIGH. Lower ONE of the outputs. Read all eight inputs, the LOW inputs have switches closed to the ONE low output. Raise the first output, lower the next one. Read the next group of eight switches.. repeat until all eight banks of eight have been read, then repeat everything from the beginning. Now, if you need more OUTPUTS (for LED's as you said) It's much the same, except you'll use two sets of eight outputs, and the diodes are replaced with LED's, and the eight of those outputs will need to be high-current (transistors will do) and you'll need eight current limiting resistors, and on and on.. I'd search a schematic for you, but I need to run an errand right now. Good Luck, Lyle

How long is your cable from the core to the display? LyleHaze

Hey wait! How many died trying? I'm enthusiastic, but not THAT enthusiastic. :-) LyleHaze

offe: Making it as small as possible? I'll admit that the display on my project, and the one encoder could be eliminated (assuming you'll control it over MIDI). But the real space-hog for me was finding roon for 8 pairs of inputs and one pair of outputs. I'm using a combination of Phone and Phono jacks, and the back of the case has filled up quickly. For a parts source I used DigiKey.com. Fair price, good service, great website. But I don't know how well they do outside the US. Stryd_One: Why do I keep it secret? That's easy. It's because I don't know yet how well it will work, and I don't want to claim that I can do something impossible. Once I have it working, then it becomes something I can brag about. ;-) No, I really don't mind telling you what I'll try. If it works, great, if it doesn't, then I'll just look foolish for trying. (won't be the first time) I figure the core won't be too busy, since it will only be passing incoming volume changes to the PGA array. so I'm planning on adding stereo VU meters and also Peak Program meters (DIN 45406). These will be routed to 4 analog inputs on the core. Now the user can select which of these can be displayed on the VFD display, and also which can be (if desired) sent back out by MIDI for remote viewing. I mean, if we are separating the control deck from the audio processing, we might need to send back a little feedback on how things are going. Finally, if I make it that far, the option of doing audio compression comes up. I could do it first from my Amiga, by watching the "virtual meters" for audio levels above or below the desired range. If I get the algorithm right, I might even try to re-write it in the PIC. I could use something like that between my bedroom TV and speakers. The broadcaster seems to turn the volume up around 3AM. I'd like to fix that. What do you think? LyleHaze

Yes. I'm still working on my PGA4311 line mixer. It has been stalled for a while as I don't have much time. So far, the case is 95% complete, and it holds a working core module and VFD display. I'm building a bipolar power supply now. The case is a 1U rack mount, so everything has to be "low profile". Fitting the display was tight. Basically, 8 stereo pairs are mixed down. I'm hoping for a few "extra features" too, but I'll not say much until they are tested. I have not yet begun the software. I want to complete the board building first. As this is a prototype I'm hand wiring the boards, I have not yet done any Eagle designs. It all would have been MUCH easier if I just threw it all together and mounted it in tupperware, but the beautiful work being shown off in "Midibox of the week" shamed me into trying to make it look a little better. You people have built some beautiful projects! What are you planning for yours? LyleHaze

True, you'll need to do a bit of soldering, but the quality of the boards is really quite good. That helps a lot. Maybe you can find a MIDIBox user in your area to help? Good Luck, LyleHaze

This is an off-the-wall idea, but how about a MIDIBOX? You can learn all about them at http://www.midibox.org Have Fun! LyleHaze

So a LTC board wired to a SMT chip with an odd driver.. At some point it just makes sense to buy a simple MIDI cable like the UNO.. Even if it is "less fun" LyleHaze

Try a search for "Yamaha CBX Driver" It'll bridge serial to MIDI.. Just might work! LyleHaze

If you want it to appear as a USB MIDI device, it will need to respond as described in the "Universal Serial Bus Device Class Definition for MIDI Devices", also known as midi10.pdf. Otherwise it'll look like a serial port.

Yes, No, and Maybe! ::) The FT-232R is capable of MIDI baud rates, which are a bit different than the usual serial stuff. But the "usual" serial port drivers that they emulate have only a lookup table for the normal speeds, so you would have to persuade the driver to let you select your own baud rate. I have lots of information on the chips, but I don't do windows, so I don't know what it's drivers are capable of. Maybe changing a lookup table entry somewhere. So you MAY be able to get 31250 baud, but how do you make it look like a MIDI device? That could be the biggest problem. It's possible to change the device codes a bit, but not to re-write the entire device, as far as I know. So let's assume the answer is NO. You CAN make it look like a serial port, since that is it's natural purpose. So the best shot you might have might be to try and use the Yamaha "ToHost" serial port -> MIDI driver. It'll let you use a "normal" serial port for MIDI, and it just might work with an FTDI USB chip! I wrote a similar driver for the classic Amigas a few years back. Again, I'm not too familiar with the windows versions, but it MIGHT work.. Maybe.. Just maybe. Have fun, and let us know what you learn! LyleHaze

Assuming phase control dimming, (the usual for Triac circuits) you might even consider small PICs for each dimmer, to handle the phase timing for you. LyleHaze

You ask many good questions. I'll try my best to answer them. What kind of caps and how many, before and after the regulator: As you can see from the cool graphics that are at the start of this thread, the job of the "smoothing" capacitors is to average the voltage across the cap. To "smooth out" the peaks and valleys. The two most important specs of a capacitor are the capacitance and the voltage rating. The capacitance tells how much smoothing you'll get (more is generally better) and the voltage rating is a maximum for that cap that you must stay below. Bigger capacitors are usually Electrolytic, these are usually polarized, and so they should have markings to show which leg is + or -. Another high capacity type is "tantalum". They have high capacity in a small package, and usually don't degrade over time like Electrolytics, but on the downside they are more expensive, and they are not tolerant of voltage spikes. How much capacitance do you need? That is math beyond my ability. It depends on the current demand of your device, the properties of your transfomer, and how smooth you need the voltage to be. Especially with electrolytics it's a good idea to go a bit over the minimum requirement, as they may vary by 20% right at the start, and will degrade with time. As long as there is load on the supply, there will always be some ripple after the first capacitors. Each regulator requires a certain voltage to do it's job. A typical 7805 may require 7 volts to assure a good 5 volt output. If the ripple (at it's worst under full load) ever falls below that minimum, the 5 volt supply will suffer dropouts. See the datasheet for your regulators to learn about the minimum input voltage requirements. The Texas Instruments sheet I just read states that the input must be 2 volts over the output for a 7805, 2 and a half for most other voltages. So if you're feeding a 7812, you'll need no less than 14.5 volts at the input under worst case conditions. The total capacitance needed may require a bigger cap than you have room for. In the case of the example given above by Ray Wilson, there are 4 4700 uF caps. These 4 together are less tall than one much bigger cap. I expect he's planning for a low profile case, like a 1U rack case or something. So if it's about "total capacitance", why include a dinky little 1uf or 0.1 uf ceramic? These smaller caps are more effective at smoothing higher frequencies. The main ripple in the supply will be at 100Hz or 120Hz, depending on your country, but much higher frequencies can be stopped much better with little ceramic caps. OK, all that for the "smoothing Caps", now on to the regulator. The popular 78xx and 79xx regulators are "linear" devices. They require a bit more voltage on their inputs in order to provide a smooth, clean regulated output voltage. As an example, let's say we have about 15Volts DC, and we want regulated +5 and +12 volts. We supply the mostly smoothed +15 volts to the input of the 7805. The output should show something very close to +5 volts. We do the same with the 7812 regulator, and we get 12 volts out. It all tests fine, so we connect our toys, and after a few minutes, it shuts down with a burning smell. What happened? These "linear" regulators have to "burn off" the difference in voltage between the input and the output. The greater that difference, and/or the greater the current, the more heat is generated. In our example, we might be drawing 50ma at 5 volts. The difference between +15 volts in and +5 volts out is 10 volts. that 10 volt difference at 50ma = 500 mw of heat (1/2 watt) That's a bit warm. Now try 500 ma at +5 volts, and suddenly you're dissipating 5 watts through your little 7805 regulator. This is why heat sinks are needed. They are radiators that help to dissipate that heat into the air. Here's a tip. the positive 78xx regulators happen to have their mounting tab at ground. So you can mount them directly to your metal project case, which should be grounded anyway. This lets you use your case as a big, free heatsink. Don't try that with the negative regulators though, their tab is not grounded. Get a bit of "thermal paste" or "thermal grease" and put a dab between the tab and heatsink. It'll help carry the heat across to the heatsink. After the regulator, there are a few more caps, though not usually as big as the previous ones. These help to smooth the load being placed on the regulator. It is also a common practice for smaller ceramic caps to also be placed at each chip. These help to reduce spikes generated by (especially digital) signals being created. You asked about the "extra" diodes and resistors in Seb Francis' designs. These may be needed for some systems. Here's what they are about. Some regulators require a minimum load to regulate well. Many designs have a very light load, especially on the negative supplies. Adding a load resistor may help the regulator to do a better job. In some systems, when the device is turned off, the input voltage may fall faster than the output voltage. This is a bad thing for the regulator. If your input voltage is gone, and you still have a bit of charge in the caps after the regulator, the regulator may be damaged. Adding a diode from the regulator output to the regulator input prevents this problem. Another diode that is sometimes added is from the output voltage to ground, so that if ground ever rises above VOut, the diode will shunt that voltage. You can see examples of all these things if you download the data sheet for a TI 78XX regulator. Finally, extra rectifiers to drop the voltage? You'll drop between 0.7 and 1.4 volts per diode, but it all adds up to the same amount of heat. You're just moving some of it from the regulator to the diode. That works. You can also get high wattage resistors to drop the voltage. Just calculate for the maximum current you'll be drawing, and make sure that the result never falls below the input voltage required for your regulator. I know these answers are for an old question, but I think power supply basics are useful for a lot of people here. I hope this response helps someone. LyleHaze

And now for new data on an old topic.. I have loaded and run the benchmark application on my MidiBox core. V1_9B, 18F452 @ 40Mhz Since my interface and OS were not benchmarked previously, I thought some might find it interesting. I'm running an Edirol UM-880 USB midi interface, which offers "HDMR" (Hardware Direct MIDI Routing). I always wanted to know how fast it really was. Running Core 1_9B, I got 1235 to 1247 0.99ms 1.0ms Jitter .005 Pretty good stuff. Then, patching the MIDI through the 880 to my computer, using CAMD library and "MidiThru" at priority 0, 2464 to 4218 1.97ms 3.37ms Jitter 0.7ms This is running through OS4 on an AmigaOne computer. Looks like it's at least comparable to some of the other types of computers. LyleHaze

A few spares are a good thing. Have Fun, LyleHaze

That circuit will work, but it adds to the load of the 7805, which you're already expecting to supply to 4 cores and an LCD display. Would be better if your second transformer could do it's voltage without piggybacking above the 5 volt regulator. Getting better.. LyleHaze

I have never seen a bridge connected in the manner you have chosen. I cannot predict with certainty what you'll get. I can, however, see a few problems that you won't appreciate. For starters, you have decided again to ground at the transformer. This is usually done for bipolar supplies. (bipolar means both positive and negative voltages are needed) Now let's walk through this: If the bottom of S1 is our reference 0V, then the junction between S1 and S2 will be positive half the time, and negative half the time. (Alternating current) Since you only need the positive voltages, you will have to lose half of your potential power at this point, or pass it on to your regulators and toast them. The top of S2 will be twice the voltage of the top of S1. But it will also be positive half the time, and negative the other half. So again, same problem as with the other junction, just twice the voltage. So, without even looking at your "unusual" bridge configuration, you have set yourself for your "best possible" setup being half-wave rectified, which is a waste of transformer capacity, and very difficult to smooth out. Now I'll qualify my comments. I'm not an electrical engineer, though I do have a good amount of experience in small circuit design. I do not have the expertise of some others on this list. I'd like to think I have some experience in explaining technical topics in an accessible way, but my word is NOT the final nameity. If you really want to build that circuit, even though I've tried to explain the problems it will have, please go right ahead. There is no better way to learn than by doing. Just make sure your power supply is properly fused. Good Luck, LyleHaze

OK, now you're "getting there". Good Job! It has nothing to do with the primaries. It has everything to do with the secondaries! Yes, if you can find a transformer with 4 6V@1A secondaries, it will do it all. Actually, 3 would be enough if you only need 6V @1A Each secondary is "isolated" from all the others, until the designer starts connecting them. (like your series connection between S1 and S2) Connect 2 in series, and you add the voltages (6V@1A + 6V @1A = 12V@1A) Connect 2 in parallel (assuming equal voltage) and you sum their current capacity. (6V@1A + 6V@1A = 6V@2A) Connect 2 in parallel if the voltage is unequal, and you have a problem. Connect out of phase with each other, and you have a problem. That's why the phase is marked with a dot. How can I help refine your understanding? Ask questions! LyleHaze

Or, Use 2 transformers.. Even the same one you have now (got a second one?) Connect one transformer with series secondaries for 12VAC @1A Connect the second transformers secondaries in parallel for 6VAC @ 2A You have choices. Good Luck, LyleHaze

Go back to the 12V bridge. Use multiple 7805's 2, maybe even 3 of them #1 for first two cores #2 for the last 2 cores #3 for the LCD display. Then a 7812 for your SID chips. All on a common ground. It's not the most "elegant" solution, but it'll work well. Hey, 7805s are cheap. LyleHaze

Well, if you must, OK. GND the bottom of S1. Connect the top of S1 to the bottom of S2, and to the Anode of a diode. take the cathode of that diode to a filter capacitor as +VLow Connect the anode of another single diode to the top of S2. take the cathode of that diode to a filter capacitor as +VHigh. Each supply is now Half-Wave rectified. You'll need to double the size of your transformer to supply the same current. You'll also need to more than double the size of your capacitors to cover the (over) 50% loss of power. There will be a LOT of ripple in this supply. I hope you're not using it for anything that needs smooth power. Good Luck, LyleHaze

After looking closer, your last drawing would be supplying the 7805 with negative voltage. This is outside the specs for the regulator, and would result in "bad things" Input voltage (at pin 1 of regulator) may not go below the GND reference at pin 2 of regulator. LyleHaze