Jeff wrote:
>I don't quite follow this - the 5V output that does _not_ run when the fan is on? You mean it runs with the fan off, but not when the fan is on? If the fan is not on, there shouldn't be any power coming out at all should there? I've never seen this. Is this on the motherboard connector? I only ever use the disk drive power connectors...
The purple wire on the motherboard connector is a +5 V out and it does not require the fan on. As long as the power supply is switched on, +5 V is coming out of the purple wire. The purple wire also only has a 2 Amp output so it is perfect for digital applications. Plus in comparison to the red wire +5 V there is far less noise when I observed them on my oscilloscope. If I wasn't running wireless, the purple wire would have been clean enough to run my application, or at least it appears so. I have not tested my application for a long period of time yet.
I also wanted to thank all you guys for your suggestions. I sorted out my noise problems. It is so wonderful to be able to ask for help when figuring things out.
Jessica
>From: Jeff Mann <jeff@xxxxxxxxxxxx>
>To: "Arg-List@Interaccess. Org" <arg-list@xxxxxxxxxxxxxxx>
>Subject: Re: ARG: RE: Re: How do I get rid of noise spikes on my Power lines
>Date: Mon, 16 Aug 2004 22:14:00 +0200
>
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>Hi all -
>
>Jessica wrote:
> >>application. If I use the +5 V output that does not run when the
> >>Power supply's fan is on, my wireless network works perfectly.
>
>I don't quite follow this - the 5V output that does _not_ run when
>the fan is on? You mean it runs with the fan off, but not when the
>fan is on? If the fan is not on, there shouldn't be any power coming
>out at all should there? I've never seen this. Is this on the
>motherboard connector? I only ever use the disk drive power
>connectors...
>
> >>As soon as I turn on the other voltages
> >>and the fan in the power supply, I get noise spikes on my +5 V
> >>supply and I have no wireless communication.
>
>There are good reasons not to use the 5V PC supply for your chips
>directly; one is that it has so much power that if you mis-connect
>something or hook it up backwards, the PC supply will happily set
>fire to all your chips! The other is that it's perhaps more
>noisy/spikey than eg. a 7805 regulator, so if you have sensitive
>analog electronics, I would also recommend putting a 7805 or 78L05
>regulator on the 12V output instead. Bruce's suggestion to put the
>regulator after the long wire run is good. Just keep in mind that
>the regulator will have to drop 12V-5V= 7 volts; multiply that by
>the amount of current you need for your board, say for example 1/2
>an amp, the regulator would have to dissipate 3.5 watts, which means
>it will get very hot and need a heatsink. But for smaller amounts of
>current (just powering a few chips) it shouldn't be a problem.
>
>Having said that, I've had good luck running PIC chip circuits
>directly from the 5V of a PC power supply (with the fan running),
>even without any filter capacitors at all. I've heard a lot of
>people say this is a bad idea, and I don't disagree; just telling
>you that it worked for me. I mean, the whole point of these supplies
>is to power a bunch of chips on the motherboard, so it must be
>basically ok for that. I've even been able to run my r/c servo
>controller board, driving the motors from the same 5V supply as the
>PIC, although in that case I definitely needed filter capacitors -
>several .1uF ones you would normally put as close as possible to the
>power pins of the chips, as well as one 100uF or more to act as a
>reservoir for the small caps to recharge from. PC power supplies are
>nice because you can find them almost anywhere, and also most of
>them will work on both 110/220V, important if you're building it
>into something you want to take across the ocean. I've been able to
>find quite a few that will run with no load on them, which avoids
>the hassle of load resistors that Bruce describes.
>
>Sandor wrote:
>>>I have had great luck in eliminating spikes using 1uF nonpolar
>>>capacitors.
>
>Why use non-polarized capacitors on a DC supply? I've never seen
>anyone do that, at that size of capacitor. At 1uF, I would normally
>use a regular electrolytic plus smaller ceramics, or else a 1uF
>tantalum (but I don't like those, they're expensive and tend to
>explode, and when they do they cause a short circuit...).
>
>>>Step one. I would certainly suggest placing one across the power
>>>lines that
>>>feed the fan I would start by placing the cap as close as I can
>>>to the
>>>actual fan inputs..
>
>I wouldn't assume that it's the fan that's causing the noise; more
>likely it's the switching power supply itself when it's running
>normally (the fan being on is a good sign that it's running
>normally!). I mean, you could test it by disconnecting the fan and
>seeing if it makes any difference. I bet it won't.
>
>>>Also, I would place one across the DC power lines
>>>wherever they enter any circuit board after running along a cable.
>
>This is a good suggestion, but again, why use non-polarized caps
>instead of just normal electrolytics?
>>>
>>>Step three. After having done the above, I still had intermittent
>>>spike
>>>problems, although they now occurred at different times. I found
>>>that
>>>placing a 1uF nonpolar cap across from Signal to GND where those
>>>wires
>>>entered a circuit board, completely cleaned up absolutely every
>>>spike.
>>>Unfortunately it also cleaned up all my data pulses too. In order
>>>to get
>>>around this I substantially lengthened the duty cycle for all my
>>>data pulses
>>>until they were of a long enough duration to get past the cap.
>>>To do this I
>>>just used a whole bunch of NOP instructions.
>
>Well, that's certainly a creative/unconventional approach! Good if
>it worked for you, but I wouldn't suggest large caps on signal lines
>for everyone. (b.t.w. I think we've changed subjects here from power
>lines to signal lines...) yes you'll have trouble sending 5V
>TTL-type data signals across long wires; this will have more to do
>with transmission-line effects than spikes per se, and get worse the
>longer the wire and the faster you try to send data. At some point
>it makes sense to use a line driver chip, eg. RS485.
>
>cu later <Jeff
>
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