，求帮助，脱离CPU，实现每23.6ms发送一个50us的脉冲？

超級狗

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你表列的其中一個網站！

http://gc.digitw.com/Program/NE5 ... er%20Calculator.htm

6 m0 J, y& B, X/ q+ I2 |7 QR1 的值必須大於 1K，C 的值也必須大於 0 .0005 uF！

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{:soso_e113:}

jacklee_47pn

超級狗 发表于 2013-6-10 11:07
9 u2 o0 B; d+ F" v7 {你表列的其中一個網站！
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http://gc.digitw.com/Program/NE555-CALC/555%20Timer%20Calculator.htm

狗版主這是為什麼呢?  DATASHEET 根本沒有標示啊！

是不是 DATASHEET 裡面所說 Output-pulse rise time 和 Output-pulse fall time 決定了最高頻率，所以計算 R 和 C 結果不得低於 Output-pulse rise time 和 Output-pulse fall time，是這樣嗎?

超級狗

jacklee_47pn 发表于 2013-6-10 19:23
5 P; x! [# M% Z, T( ~' Y, S狗版主這是為什麼呢?  DATASHEET 根本沒有標示啊！
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2 a/ Z3 `  E6 u/ f3 A是不是 DATASHEET 裡面所說 Output-pulse rise ti ...

Manufacturers specify the maximum total resistance that may be used with their particular variant of the 555, and these maximum values are usually around 10 to 20MΩ, however using such high values can increase the error between calculated and actual frequencies, so for many uses a 1MΩ maximum can be recommended. The minimum total resistance value for the combination of R1 and R2 depends largely on the value of R1. The junction of R1/R2 is connected to pin 6 and to the trigger input pin 2. If the value of R1 is less than about 1KΩ, there is a danger that the trigger input may not be able reach a low enough voltage to trigger comparator 1, and so oscillations cannot take place.

% W7 h% U  |, B! a- A) QFrom this it can be assumed that if R1 must be 1KΩ or above and R1 + R2 should be kept below 1MΩ; a 10nF capacitor would allow a suitable total resistance of around 100KΩ to be calculated.
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{:soso_e162:}

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超級狗

樓主看到的應該是另一篇文章：
Design equations:
Charge time (output high): 0.693*(R1+R2)*C
Discharge time (output low): 0.693*(R2)*C
+ A( m- ]# B3 ^% A  OPeriod: 0.693*(R1+2*R2)
  G; b6 w& W! w# h  ~! {. }2 rFrequency: 1.44 / ((R1+2*R2)*C)
2 \) u+ A# B" C! PDuty cycle: Time High / Time Low: (R1+R2) / R2

% Q' f+ r/ _8 h# t6 G: HWith a 5-volt supply, the resistors can range from 1KΩ (minimum value of R1 or R2) through 3.3MΩ (maximum value of R1 and R2 in series). Best results are obtained with capacitors of 1000pF or larger, but smaller values can be used with lower values of R1 and R2.
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jacklee_47pn

超級狗 发表于 2013-6-11 01:08
樓主看到的應該是另一篇文章：
Design equations:
6 |! M* n/ s/ Z3 dCharge time (output high): 0.693*(R1+R2)*C

狗版主真是上知天文，下知地理，跋山涉水，翻山越嶺、披星戴月，三顧茅廬，七出奇山，藉著東風，重出江湖，寶刀未老，九牛二毛，殺雞用牛刀，將死了十幾年了驗出死因。了不起

超級狗

jacklee_47pn︰既沒押韻、也不通順，辭不達意、還有錯字！ ===> 這叫【狗屁不通】 ＞_＜！！！

' ^: }- o5 ?* I$ Y" Y9 E一起辭了版主吧！
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{:soso_e140:}

fresco_xy

用一个门电路组成振荡电路加单稳态电路，用2个电位器分别调频率和单稳时间