I forgot to order the 22pF caps for the crystal....
Posted by jgilmore
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I forgot to order the 22pF caps for the crystal.... February 14, 2010 10:55PM |
Registered: 16 years ago Posts: 438 |
I forgot to order the caps, and mouser wants >$6 for shipping, so it'd be kind of silly to order 4 $0.08 parts....
I was wondering about the practicality of making them with a bit of wire... 22pF is hardly any capacitance at all, I'm wondering if I even really need it. The wire to the crystal itself as at least a couple pF of capacitance, I'd imagine.
From what I understand, I don't need it to do the ICSP and load a bootloader, but I will need the crystal to actually load a program or communicate with the chip otherwise.
I was thinking of taking a bit of 3mm plastic stock and winding a couple of wires around it 4 or 5 turns, as closely spaced as I can without shorting them, and tight enough to dig into the plastic a bit. Maybe heat them up a bit to make them stay in place... That should make a small capacitor. I have no way of measuring the capacitance, but I wouldn't think it'd be hard to get up to 22pF. Or perhaps there's a more effective way?
The alternative is to go without, and hope it works, or wait till Thursday night, when I'll hopefully be able to get to the local radio shack, and then wait till next Monday night when I'll finally have time to do something with it.
I don't like the idea of waiting a week.
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I'm building it with Baling Wire
I was wondering about the practicality of making them with a bit of wire... 22pF is hardly any capacitance at all, I'm wondering if I even really need it. The wire to the crystal itself as at least a couple pF of capacitance, I'd imagine.
From what I understand, I don't need it to do the ICSP and load a bootloader, but I will need the crystal to actually load a program or communicate with the chip otherwise.
I was thinking of taking a bit of 3mm plastic stock and winding a couple of wires around it 4 or 5 turns, as closely spaced as I can without shorting them, and tight enough to dig into the plastic a bit. Maybe heat them up a bit to make them stay in place... That should make a small capacitor. I have no way of measuring the capacitance, but I wouldn't think it'd be hard to get up to 22pF. Or perhaps there's a more effective way?
The alternative is to go without, and hope it works, or wait till Thursday night, when I'll hopefully be able to get to the local radio shack, and then wait till next Monday night when I'll finally have time to do something with it.
I don't like the idea of waiting a week.
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I'm building it with Baling Wire
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Re: I forgot to order the 22pF caps for the crystal.... February 15, 2010 01:18AM |
Registered: 16 years ago Posts: 1,094 |
the capacitors keep the crystal frequency stable and provide a measure of noise immunity. It will probably run ok with no capacitors at all, but may fail underneath lots of fluorescent lights or within 200m of an arc welder or when a storm is building.
see what happens without them, and at the same time try to obtain some. maybe cannibalize?
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Wooden Mendel
Teacup Firmware
see what happens without them, and at the same time try to obtain some. maybe cannibalize?
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Wooden Mendel
Teacup Firmware
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Re: I forgot to order the 22pF caps for the crystal.... February 15, 2010 06:34AM |
Registered: 16 years ago Posts: 438 |
K. I'll do that. I'll be running it via the laptop on a modified sine wave inverter. That's got a lot of noise, here's hoping it doesn't interfere...
I'm also assuming that the vastly larger 100nF (~500x greater) caps I have won't do. Though I suppose they might for a (vastly) lower frequency.
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I'm building it with Baling Wire
I'm also assuming that the vastly larger 100nF (~500x greater) caps I have won't do. Though I suppose they might for a (vastly) lower frequency.
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I'm building it with Baling Wire
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Re: I forgot to order the 22pF caps for the crystal.... February 16, 2010 05:57AM |
Registered: 16 years ago Posts: 1,094 |
lol I think putting 100nF caps on it would stop the oscillation completely
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Wooden Mendel
Teacup Firmware
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Wooden Mendel
Teacup Firmware
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