Oscillators/Resonators, not all the same....
LoopyByteloose
Posts: 12,537
Hi,
I have just been reading Sx-Ubicom's literature and Gunther's book.
It appears that all the PARALLAX boards require oscillators/resonators which include their capacitors internally.·
While it is a much cleaner board that way, I am a bit worried that I will have trouble getting these locally [noparse][[/noparse]the language barrier].
What is the risk of damage if you insert a resonator· [noparse][[/noparse]one which has no capacitors included] without the accompanying capacitors?
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
G. Herzog in Taiwan
I have just been reading Sx-Ubicom's literature and Gunther's book.
It appears that all the PARALLAX boards require oscillators/resonators which include their capacitors internally.·
While it is a much cleaner board that way, I am a bit worried that I will have trouble getting these locally [noparse][[/noparse]the language barrier].
What is the risk of damage if you insert a resonator· [noparse][[/noparse]one which has no capacitors included] without the accompanying capacitors?
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
G. Herzog in Taiwan
Comments
The caps give the oscillator circuit inside the SX the correct phase delay to operate properly.
Without the caps you may get irratic behaveour or no oscillation.
You should be able to use seperate caps on either side of the resonator.
Bean.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"SX-Video·Module" Now available from Parallax for only $28.95
http://www.parallax.com/detail.asp?product_id=30012
Product web site: www.sxvm.com
"One experiment is worth a thousand theories"
·
I went to the parts store to simply by some 8Mhz resonators for the X-52, what I got were 3 items:
[noparse][[/noparse]1] ceramic filter elements at 4.5mhz and 6.0mhz
[noparse][[/noparse]2] 24mhz oscillator in retangular package for 16pin DIPs, 4 leads
[noparse][[/noparse]3] generic 2 lead, metal case 4mhz and 8mhz crystals.
None of these are truly the little resonators that I wanted. I have made the following assumptions but really need help.
A.· Ceramic filter elements are FILTERS and may not work at driving an oscillation.· These may be useful in the future if I had a problems with EMI or RFI, but I wasted my money.
B.· The Large retanguar package may work if I only have to plug in two pins -· Further research is needed.
C. I can actually add two capacitors to the generic crystals, hot glue them to the case, solder on side to the crystal leads, create a third common ground lead and have a workable, though large-ish device.
My frustration abounds and I am sure some of you are beginning to understand why I proceed so slowly.· Being in a foreign country with a substantial language barrier means a lot of creativity and patience.
If I could just plug in #1 or #2 I would be ahead of the game [noparse][[/noparse]I can buy #2 in 4Mhz and 8Mhz at another store, but already had gotten the 24Mhz to try at the first store].
By the way, after months of asking I was actually able to buy 5 MAX232!·· So, imagne I just have to keep going back and asking to get many popular parts.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
G. Herzog in Taiwan
Post Edited (Kramer) : 9/2/2005 3:17:53 PM GMT
Anyway, he sells them via eBay. A good deal, and the shipping is not too expensive. http://search.ebay.ca/_W0QQfgtpZ1QQfrppZ25QQsassZspeff is his eBay listing.
A. Yes - filters simply filter, or suppress a certain frequency, or a frequency range, or filer out (select) a certain frequency, supressing other frequencies. I assume that you have acquired selective filters. These usually are used in superhet radio receivers for filtering the so-called "intermediate" frequency (IF). That is - whatever RF frequency you want to receive, it will be mixed down to the IF, so the signal can be amplified by an amplifier designed for just one frequency, the IF. Theoretically, you can use such filters for oscillators as well but I think the SX-internal oscillator circuit is not capable of driving such filters.
B. It seems to me that this component is a complete active oscillator. It will need a power supply (Vdd and Vss) connected to two of its pins, and it will generate a 24MHz clock signal on one of the remaining pins. This signal can be fed into the SXes OSC1 pin (OSC2 remains unconnected in this case). So, this operates as an external oscillator.
C. Yes, it looks to me that these are crystals possibly requiring extenal capacitors. I would try the crystals w/o additional capacitors first - just connect the two pins to OSC1 and OSC2 and see if the SX is clocked by running a simple LED blinker program.
What Parallax boards are you referring to? If you are using a SX48/52 Proto Board, you may be lucky and item #2 fits into the provided socket. BTW, Parallax did a good "design trick" here. You can't plug in the SX-Key, as long as the oscillator module is plugged in. IOW, you need to unplug the oscillator module before connecting the SX-Key because both items must not be connected to the SX at the same time.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Greetings from Germany,
G
GUENTHER
Actually, I am refering to all the Parallax SX-Ubicom boards, but in particular to my SX-28 programer and my SX=48/52 Proto boards.·
The little 3-pin resonators are great, but apparently overseas availablity may be a problem.· I strongly recommend that anyone buying the SX-28 or the SX-48 or SX-52 get an assortment in the same order.· I made the mistake of thinking that everything should run at 50Mhz, but the power drain is quite high [noparse][[/noparse]over 10 times that of 4Mhz].
I talked with a Taiwan manufacturer's that I teach English and he keeps telling me that he doesn't support anything that uses DIP or SIP·- it has all gone to Mainland China.· So, this may be a problem that only exists in Taiwan.· Being a major player in the electronics manufaturing,·Taiwanese are very reluctant to get caught with out-dated inventory and want to keep their position by using the latest technology.·
Also, I cannot locally find a Parallel Printer card to plug into the backplane of my computer.· They just tell me that nobody needs that anymore [noparse][[/noparse]but we know many of the programers for chips still use parallel].
In sum
Item #1 appears useless for now.· Can anyone think of a hobby application for a 4.5 Mhz or 6.0 Mhz bandpass filter?· It seems that it might clean up a problem somewhere and somehow?
Item #2 is too big.· The SX-48-52 uses what look like an·10-DIP footprint [noparse][[/noparse]it is square.].·I would have to build an adapter [noparse][[/noparse]which I may do later·because I can get a lot of these in various frequencies].
Item #3 appears to be the winner.
After looking at the schematic and what I had, I came up with a QUICK FIX - VERY CLEAN.
I am posting a photo of my own 'quickie' solution. PLEASE NOTE THE RED ARROWS. If this works, it offers a very simple 4th alternative to ANYONE using the Sx-48/52 Protoboard.
I just plug in two capacitors [noparse][[/noparse]30pf] and a crystal [noparse][[/noparse]4mhz] by using three of the sockets individually.
The wiring is right, but I wonder about spreading oscilator components around. Will this in some way destablize their usefulness?
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
G. Herzog in Taiwan
Post Edited (Kramer) : 9/3/2005 12:47:49 PM GMT
Then again, there is an engineering study that suggests that bumble bees can't fly, so try it (not the flying part!) and see what happens.
Later!
kenjj
PS why in the dingdong is carriage return producing two swingin' new lines on this mail?!
It's uglier and bulkier than I'd like, but it works.
I haven't really done that yet.
I suspected that in the long run something about just pluging in three parts would give me trouble. I will solder up a unit and add some hot glue.
I imagine that a capacitor would come loose when most inconvient.
Still, it is a 'quickie' bench test.
One more question,
Can I use the same capacitor values be used for SX-52s as for SX-28s?
I assumed that the two chips have the same oscillator driver when I purchased capacitors. I am still digging for my SX-52 specifications from SX-Ubicom.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
G. Herzog in Taiwan
Post Edited (Kramer) : 9/3/2005 12:49:44 PM GMT
The SX-28 at 4Mhz has C1 at 15pf and C2 at 22pf with an Rf of 1Mohm [noparse][[/noparse]Fuse setting 010]
··············· At 8Mhz has C1 at 56pf and C2 at 33pf with an Rf of 1Mohm [noparse][[/noparse]Fuse setting 011]
The SX-48 or SX-52
··············· At 4Mhz has C1 at 33pf and C2 at 56pf with an Rf of 1Mohm [noparse][[/noparse]Fuse setting 011]
··············· At 8Mhz has C1 at 22pf and C2 at 56pf with an Rf of 1Mohm [noparse][[/noparse]Fuse setting 011]
I suspect that you will have an oscillator regardless of getting it right or wrong - just not the frequency you want to hold at.· Also, the simple RC circuit of one resistor and one capacitor at .1% accuracy looks mighty useful for merely driving a set of servos. [noparse][[/noparse]NOTE - This is wrong, the External RC is quite problematic. After re-reading the documentation I suspect it is limited to 4Mhz - it doesn't say -·and subject to stray capacitances and other interferances.· So, I suppose the Internal Oscillator is just as good or better.· The RC circuit is trivial unless you want a tunable low frequency.]
I am finished asking any questions about this until I actually acquire both a scope or frequency counter with appropriate bandwidth [noparse][[/noparse]75-100 Mhz] and a capacitance meter.· It seems that the circuit board alone could provide your capacitace or throw it off the mark.
The TTL oscillators [noparse][[/noparse]in the tin cans with 4 wires that plug into a DIP]·are quite nice and by far the most reliable DIY solutions - no scope is needed.· But my 24Mhz draws 30ma of current. That seems about equal to the SX-28 at that frequency.· Not exactly micropower, but very useful at the higher frequencies.
Thanks again for the help.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
G. Herzog in Taiwan
Post Edited (Kramer) : 9/3/2005 12:57:38 PM GMT
wait a second - for the SX48/52 Proto Boards, you don't need to build this "crytal - capacitor - ho glue" monster. Just plug the crystal into the two outer positions of the X2 connector. If the crystal's wires are further apart, try to plug it into the two outer positions of the X1 connector. Plug one capacitor into positions X0 and G of the Cx connector, and the other one into positions X1 and the other G.
Too bad that I did not study the SX48/52 Proto Board schematic in more detail before.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Greetings from Germany,
G