wickedblade
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wickedblade [2009/12/15 15:09] WickedBlade |
wickedblade [2011/11/29 14:40] (current) smashtv old revision restored (spam kill) |
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| But this is the maximum continuous current draw, we have to take the pikes into account too. I've been told that aiming at 2A is a good choice, so I'll try to do that. | But this is the maximum continuous current draw, we have to take the pikes into account too. I've been told that aiming at 2A is a good choice, so I'll try to do that. | ||
| - | I originally decided to go with a 9V power supply, because they are common in guitar effects gear. Most power supplies only provide 500mA, but I've managed to find a 9V 1A power supply. I thought that translated into 5V, that would mean that I should be able to draw 1.8A from these, which whould have been enough. Unfortunately, the 7805 voltage regulator is linear, which apparently means that it won't provide more current at 5V than it would draw at the source. | + | As far as voltage is concerned, the PIC and associated ICs need 5V, the relays need 5V too, but for the input/output buffers opamp, I need to get as much headroom as possible. 9-10V might do the trick. Given that voltage regulator tend to drop about 2V from their input voltage, I've decided to go with a 12V power supply. There are plenty of 12V 2A power supplies available, but they tend to be switching PSU, which we do not want, because they often add unwanted noise. I've found a linear 12V 1.5A PSU instead at Thomann, the THOMANN NT 1215 C unit, which is a replacement for Casio products. It is indeed linear (I've ordered it blindly, but it turned out good), the only caveat is that it has a plug that is not the "usual" DC 2.1mm jack, but it's easily swapped for anything you like. |
| - | Since then, I found a 5V 2A power supply (PETERSON POWER SUPPLY 5V 2A at Thomann), which is significantly more expensive, but ensures that I won't have power supply problems. Also, the 5V input voltage means that the 7805 won't heat much, I think. | + | |
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| - | I also found a 9V 2A unit: THOMANN NT 092A, similarly priced. | + | |
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| - | I thought for a time that I could forget about these power supply units: the Sony PSP portable console uses a 5V 2A power supply, so that means that there are many that are readily available in video game stores, for a much lower price. I purchased one and it is indeed a 5V 2A supply. However, using a 5V power supply would mean getting rid of the voltage regulator, since these have a ~2V voltage dropout that makes them rather inoperant if fed with less than 7V. This is perfectly acceptable in some cases, but I'd rather keep the voltage regulator and associated bridge rectifier and caps, because they provide some sort of protection against wrong voltage and polarity, whereas if I just use a 5V supply I may fry the PIC (or other stuff) if I accidentally use a 9V power supply from my other effect pedals. So I have to revert to using a 9 or 12V 2A power supply. I happen to have a couple external cases for 3.5" hard drives, and these are fed with a 12V 2A power supply, so I think I'll use that, and I'll purchased a new power supply only if it turns out that I have too. | + | |
| It appears to me that I need to manage 2 separate grounds for analog signal and digital signal. I don't quite know how to do that. I've been told I could put some kind of low pass filter somewhere, but I don't quite know how and where. I believe this should go between the digital and analog grounds, so that the analog ground gets a filtered version of the digital ground, but how should I go about it? | It appears to me that I need to manage 2 separate grounds for analog signal and digital signal. I don't quite know how to do that. I've been told I could put some kind of low pass filter somewhere, but I don't quite know how and where. I believe this should go between the digital and analog grounds, so that the analog ground gets a filtered version of the digital ground, but how should I go about it? | ||
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| * For use as a computer MIDI interface, you really need either a gameport MIDI cable (if you motherboard has a gameport) or a USB MIDI cable. I now know for a fact that my Line6 PODxt and my Boss DR-880 can't be trusted, even though they sport USB and MIDI outputs. The PODxt filters out SysEx messages and I couldn't get my DR-880 to forward anything. | * For use as a computer MIDI interface, you really need either a gameport MIDI cable (if you motherboard has a gameport) or a USB MIDI cable. I now know for a fact that my Line6 PODxt and my Boss DR-880 can't be trusted, even though they sport USB and MIDI outputs. The PODxt filters out SysEx messages and I couldn't get my DR-880 to forward anything. | ||
| * Noise! It turns out that having the DOUT modules chained is a recipe for noise. Specifically 1kHz noise (if that's the frequency to which you set the shift registers refresh). After a hard time investigating, this gets fixed by star-grounding the grounds of each module to the ground pin of the big cap connected to the voltage regulator on the CORE module. | * Noise! It turns out that having the DOUT modules chained is a recipe for noise. Specifically 1kHz noise (if that's the frequency to which you set the shift registers refresh). After a hard time investigating, this gets fixed by star-grounding the grounds of each module to the ground pin of the big cap connected to the voltage regulator on the CORE module. | ||
| + | * The documentation about MIOS_BANKSTICK functions is unclear about that, but it seems that if you want to use the page reading/writing functions, you MUST have aligned adresses (i.e. adresses where (addr & 63)==0 ), otherwise all kinds of trouble appear | ||
| + | * I would have dearly loved to know about the watchdog timer (WDT) before, that would have helped me understand why my app kept rebooting while it was trying to initialize the banksticks! Days on debugging have been wasted on this :( | ||
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wickedblade.1260889762.txt.gz · Last modified: 2009/12/15 15:09 by WickedBlade
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