27MHz 遙控車, 修修補補後, 破碎的遙控恢復工作, 但是遙控距離只有一米左右


http://wp.me/ph3BR-ok

 

REVIEW

 

 

27MHz 遙控車, 姪兒的被破碎的玩具

https://xiaolaba.wordpress.com/2012/01/25/27mhz-%E9%81%99%E6%8E%A7%E8%BB%8A-%E5%A7%AA%E5%85%92%E7%9A%84%E8%A2%AB%E7%A0%B4%E7%A2%8E%E7%9A%84%E7%8E%A9%E5%85%B7/

終於有時間坐下來, 繼續學習一下無線電 RADIO CONTROL.

雖然還是一知半解, 但是畫了線路圖, 示波器看了波形, 幾本上又了解了更多關於無線電的資料.

修補的工作, C2 不見了, 用了40pf 補上, C6 斷了, 隨便換了100pf, VDD 斷線, 確認後補線, 遙控的距離只有10CM.

MOTOR CONTROL 的橋式正反轉電路, 動作正常.

調節接收器的 LC 震盪, 頻率 25.51MHZ, 並不是發射的27.145MHZ, 遙控的距離增加到1米, 可惜還是線不夠遠. 因為天線等配件都留在姪兒處, 所以猜想是天線的阻抗不匹配, 發射功率或頻率受到影響, 可是實際原因還是不太理解.

網上找到的資料, 關於27MHZ遙控車的, 雖然 IC RX-3E 沒有確切的資料, 但是參考 RX-3, 比對自己畫出的線路圖, RF 的設計是一模一樣的.

到此為止, 遙控車的發射接受線路都完整劃出來, 對於無線電是學習的一個進步.

總結一下遙控電路的基本配置,

遙控器的 [前進] [後退] 按鍵, 提供不同電壓到, 輸出 944HZ 和 294HZ 的兩種頻率, 透過 27.145MHZ LOCAL OSCCILATOR 載波, 調製並發射

接收器的震盪器 Q1, 基極透過 R1 (180K), R2 (2K2), C4, 將接收到的 944HZ 或 294HZ 訊號輸入到 IC RX-3E 的 7 腳, 4 腳 或 5 腳則輸出, 驅動橋式正反轉電路, 使 MOTOR 正轉或反轉, 達成 [前進] 或 [後退].

至於這個遙控電路的頻率或發射距離, 則還是沒有完全理解如何設計或計算, 留待日後慢慢再學.

h_t_t_p://www.youtube.com/watch?v=fOh4IflQ6a8&feature=youtu.be

TEST H-BRIDGE of MOTOR DRIVE

h_t_t_p://www.youtube.com/watch?v=rspBSOgs97Q&feature=youtu.be

REMOTE IN FUNCTION

h_t_t_p://www.youtube.com/watch?v=XyB_oe6TxkI&feature=youtu.be

BETTER REMOTE IN FUNCTION

接收機的電路, 下面這個網頁有完整的介紹, 借用其圖片及文字, 對比RF線路, 解釋動作的原理, 以下是俺的理解和翻譯,

一個27MHz的接收機前端,與27MHz的對講機的前端略有不同。

該電路的負載很低, 這樣它會檢測微弱的信號, 並且非常敏感。供電的3K9電阻負責完成供電的任務. (2014-JAN-15 校誤)
BC547晶體管 EC 端的電壓約 2V 和流過的電流小於1mA. 電路是一個共基極放大器, 在特別設計的情況下, 這樣一個晶體管就可構成振盪器.

首先, 讓我們描述這個共基極放大器是如何工作的.

220K的基極偏置電阻使 BC547 導通. 6T的線圈在集電極成為負載,但因為它的直流電阻值很低, 需要有另一個限流電阻, 因此 680R 的限流電阻但被放置在發射極, 避免BC547燒毀. 這個電阻只限制電路通過的電流, 旁邊並連的旁路電容3N3, 允許交流通過.

有兩種方法打開BC547晶體管.

一個是固定發射極電壓, 並提供控制電壓和電流到基極。
另一個是固定基極電壓, 並且降低發射極的電壓。這正是這個電路工作得方式。

4u7的電解電容保持BC547基極電壓, 39P電容則增加或減少射極的電壓, 使BC547導通或截止.

以上的觀念必須明白,我們才可以進一步理解這個電路的概念。

該電路開始動作, 通過6T的線圈和47P電容的電流脈衝。 這兩個組件構成一個 LC 諧振電路 (LC TANK CIRCUIT),當他們收到能量,它們產生的正弦波,透過39P電容傳遞到 BC547 的射極。這是一個驚人的事實,兩個簡單的LC零件可以產生正弦波,且電壓的震盪幅度較電源的電壓高,詳細的原理不在此述,需要完全理解的話請參考其他文獻. (LC oscillator 和機械學的簡諧運動, 是同樣的原理 http://www.greenandwhite.net/~chbut/lc_oscillator.htm)
(2014-JAN-15 校誤, 原網址失效, 找到另外的 MIRROR)
http://www.ctaps.yu.edu.jo/physics/Courses/Phys102/Phys102_Web_Resources/RCV/LC_Oscillator.htm

這個LC TANK CIRCUIT 產生的震盪電壓, 最終的結果是 BC547 的發射極的電壓改變, 使其導通與截止, 形成震盪。

BC547射極的70T電感器, 目的是使射極的電壓高於0V,持續使39P電容得到脈衝, 維持震盪。

要解釋這個70T電感器是如何確切工作,是非常困難的,簡單來說, 它允許39P電容降低發射極的電壓,如果沒有70T電感存在,39P的小小電壓改變難推動3N3電容。但如果3N3電容不存在, 則 39P 電容沒有足夠的能量改變680R的電壓, 震盪便無法完成. 然而,當加入70T電感,39P改變發射極電壓的工作變得輕鬆。

儘管這是一個接收器的前端,它實際上是在27MHz 振盪器。

該電路已實際搭建並實驗,以確保70T電感和6T線圈可構成敏感的RF前端。如果沒有實際驗證, 一般模擬程序無法預測的這樣的電路設計的結果。
70T電感約7uH電感量, 在1M電阻上用很細的電線纏繞而成。 該電阻器可以是任何高阻值,實際中並沒有作用, 純粹是作為繞線電感的骨架, 電阻的碳含量沒有任何電感的影響。

原文如下-

http://www.talkingelectronics.com/projects/27MHz%20Transmitters/27MHzLinks-1.html#Receiver%20for%20Tx_A

The front end of a 27MHz receiver is slightly different to the front end of a 27MHz Walkie Talkie. The circuit is very lightly loaded so that it will detect the slightest signal and this makes it very sensitive. The component that does this is the 3k9 in the power rail. The transistor has only about 2v across it and takes less than 1mA.

The circuit is a common-base amplifier and under certain circumstances, a single transistor in this configuration will oscillate.

First, let’s describe how a common-base stage works. The 220k base-bias resistor turns the stage on. The coil in the collector is the load but since it is such a low resistance, a voltage-dropping resistor has to be placed in the emitter. This resistor only limits the current through the circuit. It is by-passed with a 3n3 capacitor and does not cone (come 錯字??) into the operation of the operation of the circuit.

There are two ways to turn on a transistor.

one is to hold the emitter fixed and deliver a voltage and current to the base.

The other is to hold the base rigid and reduce the voltage on the emitter. that is what we have done in this circuit. The 4u7 electrolytic on the base holds it rigid and the 39p reduces the voltage on the emitter to turn the transistor ON and during the other part of the 27MHz cycle, it increases the voltage on the emitter to turn it OFF. This concept must be understood before we can advance further.

The circuit starts by receiving a pulse of current through the 6t coil and 47p capacitor, when it is turned on.  These two components form a TUNED CIRCUIT and when they receive energy, they produce a sine-wave (sinusoidal) waveform that appears on the lower part of the tank circuit and this is passed to the emitter via the 39p. It’s an amazing fact that two simple components can produce a sinewave that has an amplitude larger than the voltage applied to the pair, but this is what happens and to fully explain it, would require another chapter.

However the end result is the emitter is pushed down to turn the transistor ON more and pulled up to turn it off. The 70t inductor on the emitter simply keeps it away from the 0v rail so that the pulses on the 39p can have an effect on pushing and pulling the emitter. To explain how the inductor works is very difficult, however it has the effect of allowing the 39p to push the voltage lower on the emitter, than if it were not included. If the inductor is removed, the 39p will have a very hard job to push against the 3n3. But if the 3n3 is removed the 39p will have a small difficulty pushing against the effect of the 680R. However when the inductor is added, the 39p has a much easier job of pushing and pulling the emitter. Even though this is the front end of a receiver, it is actually oscillating at 27MHz.

The circuit has been built for experiential purposes to make sure the 70t inductor and 6t coil work perfectly to price a sensitive front-end. Never put a circuit on the web without building and testing it with actual components. Simulation programs cannot predict the outcome of hand-made components. The 70t inductor is about 7uH and is wound on a 1M resistor with very fine wire. The resistor can be any high value and does not play a part in the functioning of the circuit. It is just a convenient core for the winding. The carbon content of the resistor does not have any effect on the inductance.

http://talkingelectronics.com/projects/27MHz%20Transmitters/27MHzLinks-2.html

http://pro-radio.ru/user/uploads/126799.pdf

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