Sync Project: Day 2
Jan 25, 2010 Arduino
Posted by
irfon
Today was the first day I’ve had to work on the sync project since my last update and it was a bit frustrating. I started late and I kept not finding what I needed, plus other mishaps. A lot of the evening was spent with an analog multimeter, a battery and a diced-up MIDI cable trying and failing to trace the pins, desperately trying to shove the battery back into our cordless phone and sync the phone to the base before calls went to voicemail, cutting up audio cables I had lying around to make connector cabling for the breadboard and discovering that the resulting strands were so thin that they just sort of sat gently in the sockets and would fall out at the barest gesture and other such entertaining activities.
However, I eventually did get it going and turned to the software part, which was about as fraught with banging my head on the table, but ultimately wound up with a fair bit of success. I guess that’s more evidence the perseverance is the key.
Right now, I have a device built which does the following:
- Has a push button to toggle between internal and external mode
- In internal mode, generates Din Sync which is read successfully by the Time Buffer
- In internal mode, has a knob that allows you to select tempo
- In external mode, receives MIDI Clock signals from the computer and converts them to Din Sync
- Powers itself from the computer’s USB bus
Things still to do:
- Replace button with two-position switch
- Use button or switch as run/stop toggle in internal mode
- Add recognition of sequencer run/stop/continue messages for external mode
- Add MIDI Thru if I decide that I want that
- Get power from synthesizers.com power supply or external power supply
- Swap DIN cables used currently for DIN jacks
- Install in box or behind synthesizers.com panel
All in all, most of the tough stuff is done and working now, and I pretty much have all the reference material I need to do the rest.
Oh, except for one thing. The synthesizers.com power supply has three rails I can use — +5V DC, +15V DC and -15V DC. The arduino likes to get something from +7V DC to +12V DC. If anyone has a few words or pointers for inexpensively getting from A to B on that one, please let me know. It would be greatly appreciated.
January 27th, 2010 at 8:46 pm
There’s a pretty simple way to do it using a cheap 78xx-series linear regulator.
If it works on +12VDC, then you can just feed the +15 into a 7812, and get regulated +12 out of it. A simple TO-220 (3-pin) IC that you can probably even buy at Radio Shack (errr, The Source). You can probably get away without a cap on the +15 side, since that is already regulated, but you’ll probably want a 100uF and a 100nF (for noise suppression) on the output. Middle pin goes to GND. If you do want an extra cap on the input – since AFAIK the datasheet does recomment it – something like a 1000 or 2200 uF should be plenty (even 470uF is probably OK).
With the 7812, you’re only dissipating 3V as heat, which isn’t too bad and you should be OK without a heatsink if you’re using under 200mA. You could use a 7809 (+9VDC regulator) if your current requirements are rather lower. Odds are you’re only using a few 10s of milliamps, so even a 7809 would be OK on its own.
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irfon Reply:
January 28th, 2010 at 12:43 pm
The 7809 sounds like a better bet in that it’s right in the middle of the acceptance range, so it can wobble a bit more without any problems just in case. I assume that means it’ll give off more heat?
I looked up the datasheet for the AZ7809T-E1 as just a random example. They show under “Typical Application”, the input and ground connected by a 0.33uF cap and the output and ground connected by a 0.1uF cap, and that’s it. I’m a little confused by that, since the capacitors they talk about have way different ratings than the ones you were talking about (1000 – 2200 uF on the input and 100uF + 100nF on the output).
It looks like for most of these ranges, electrolytic capacitors are the only choice, at least at the supplier I was checking out. Is that the right kind, or should I be looking at another kind? When choosing the working voltage for the capacitor, should I be comparing it to 12V on the input and 9V on the output? Is there any harm in getting something with a (much) higher WV? They’re all the same price.
Thanks for your help!
[Reply]
January 28th, 2010 at 5:04 pm
Interesting, I checked out another datasheet (NJM7809) and they specify the exact same thing. The larger electrolytic caps that I was suggesting are what I normally see in various powersupply designs that use the 78xx linear voltage regulators. I assume they’re used in case of the load suddenly drawing a spike of current.
You can probably do without them just fine, if the datasheet suggests. It will be much easier to track down 330nF and 100nF caps, probably just little ceramic ones.
But yes, in the 100uF+ range you are most likely only going to find electrolytics, which are typically used for that kind of application. Usually you want to go with at least 50% more than the maximum voltage that you are expecting to use. Most of the time you will be somewhat limited by your supplier’s options, so I end up working with 25 or 50V caps even when I’m operating around 9 or 12 volts. There’s no real harm in using a higher voltage, at least for most minor hobbyist applications (though the size of the cap will often increase).
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