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改摩打控制器

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發表於 2011-11-18 14:49:44 | 顯示全部樓層 |閱讀模式
I've bought a 126-teeth mount, but it lacks a motor and the original motor was discontinued.

In order to give it a suitable motor, I've found a motor which might be a good starting point for my hacking project.

IMG343.jpg

This motor is originally for a 180-teeth mount, and then I'll want to make it for 126T. So when I open the controller box, I can see a 5.257234MHz crystal, shall I simply change it to a similar 3.68MHz crystal?

What precaution I should have in mind when swapping crystals? I've zero knowledge here, I don't even know if they have polarity, voltage spec and they come in different shapes, so what I should keep in mind when finding for a replacement?

Thanks a lot!
發表於 2011-11-18 16:52:35 | 顯示全部樓層
回復 1# oldfield

Dear Oldfield,
Firstly you need to make sure what type of motor you are using.  controls for DC motor (they may use pulse-width for speed control, or simply voltage control), or stepper motor (the frequency of the pulse will control the motor rotation), or servo motor which needs feedback.

The crystal may be just for providing the clock pulse for the circuit, not necessarily directly related to the motor speed.

You need to know the specification of any electronic part you may like to change.  For such data, you can find in this site:

www.alldatasheet.com

pts
 樓主| 發表於 2011-11-18 17:04:19 | 顯示全部樓層
本帖最後由 oldfield 於 2011-11-18 17:12 編輯

this is a stepping motor.
發表於 2011-11-18 22:28:54 | 顯示全部樓層
一般兩腳的 crystal 是沒有極性的 passive component,除非 spec 有特別聲明 (兩腳分稱 Line 1、Line 2)。三腳或四腳的 cytstal oscillator 是 active component,有極性的,參考

http://www.maxim-ic.com/app-notes/index.mvp/id/726

如果把原有的 5.257234MHz crystal (180T) ﹕改為 3.68 MHz crystal (126 T),改後你可能要重新調校串在 crystal 腳的 capacitor trimmer 仔 才有正確的頻率 (不調校也可能照 work,只是3.68MHz 的頻率略有小偏差,你肯容忍這些小偏差便行了)

現在的兩腳 crystal 並不貴,不妨試試改裝,銲接時要小心一點,不要把原本的 crystal 腳或線路板的銅孔弄斷。
 樓主| 發表於 2011-11-18 23:07:42 | 顯示全部樓層
多謝 Alan 指點!
 樓主| 發表於 2011-12-8 17:45:35 | 顯示全部樓層
Dear Alan and all,

I've read the document here:

http://www.foxonline.com/techfaqs_cry.htm#a25

And found that there're at least two types of crystal that I might buy, given the outlook, I believe that the original controller uses HC49U but I found that HC49US is easier to buy, and it seems like the only difference that might concern me is the pullability?

And for that case, does that translate to the range that I could control by using those trimming capacitor (as told by Alan earlier)?
發表於 2011-12-8 20:44:45 | 顯示全部樓層
Dear Oldfield,

HC49U is standard size (~13 mm high).  HC49US is low-profile size (~ 5 mm high).

Since your clock circuit is using non-high frequency crystal (5.257 original  vs 3.68 MHz presumeably), I think HC49U and HC49US makes little difference in trimming capacitor.
Just try it.

Alan
 樓主| 發表於 2011-12-8 21:32:18 | 顯示全部樓層
Thanks again for your valuable comment.
 樓主| 發表於 2011-12-14 20:23:20 | 顯示全部樓層
The 3.6864MHz HC-49S crystal arrived and after my dirty soldering work, everything worked out as expected.  And after adjusting the trimming capacitor, the speed is about correct (using stopwatch for timing), and once the shaft coupler arrives, I shall test it again on the stars!

Thank Alan again for your expert advice and patience.
 樓主| 發表於 2011-12-17 12:40:24 | 顯示全部樓層
This is the alpha testing by using the sun as target:

http://osastrolog.blogspot.com/2 ... -alpha-testing.html
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