新研究了個東東，家裡的廢舊顯示器終於有了利用價值
阿新 • • 發佈：2020-02-05
這些年下來，家裡，公司有很多廢舊的電視機，顯示器，投影機。你說扔掉吧，有點可惜，賣給收廢品的吧，其實和扔也差不多。總想著怎麼把這個淘汰下來的顯示器給利用上呢。
這些顯示器都有個共性，就是帶有VGA介面。上網搜尋研究了一下，發現VGA介面是可以程式設計驅動的。
VGA的電氣介面除了GND以外，基本的必須有5條訊號線：hsync行同步,vsync場同步,red紅,green綠,blue藍。VGA的時序要求是比較嚴格的，差一點點都無法正常顯示。具體的VGA時序，這裡就不贅述了，大家可以網上搜索一下。
由於我打算用微控制器實現VGA的時序，使用STM32F103測試後可以實現，但由於103的記憶體太少了，畫素的計算搬運有點吃力，最後還是決定使用STM32F4，手頭剛好有F401,主頻84M,記憶體64K,足夠我使用了。
我這裡設計的是一個320*200（橫向320個點，縱向200行）的VGA輸出音樂頻譜模組，基本引數如下：
電源電壓：DC5-12V
工作電流：<30mA
頻率響應300-18kHz
聲道數：2
為了能夠穩定輸出時序，使用了兩個定時器中斷分別輸出行頻和場頻。其次需要對音訊進行40Khz的高速取樣，這裡也使用了一個定時器+DMA,最後還需要對音訊進行RFFT運算，得到幅值後轉換為畫素顯示。前前後後打了5次PCB,花了將近4個月的時間完成，中間也遇到不少坑，這裡只把最後的成果展示一下，作為疫情宅家紀念。
關鍵程式碼：
使用TIM1和TIM2分別做為行輸出和場輸出訊號，在行輸出中斷中，使用GPIOB傳送顏色訊號，在場消隱中計數，並復位影象顯示頭部。
void TIMER_Configuration(void)
{
GPIO_InitTypeDef GPIO_InitStructure;
NVIC_InitTypeDef nvic;
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
u32 TimerPeriod = 0;
u16 Channel1Pulse = 0, Channel2Pulse = 0, Channel3Pulse = 0;
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_1 | GPIO_Pin_8;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_DOWN;
GPIO_Init(GPIOA, &GPIO_InitStructure);
GPIO_PinAFConfig(GPIOA,GPIO_PinSource8,GPIO_AF_TIM1);
GPIO_PinAFConfig(GPIOA,GPIO_PinSource1,GPIO_AF_TIM2);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0|GPIO_Pin_1|GPIO_Pin_2|GPIO_Pin_3|GPIO_Pin_4|GPIO_Pin_5|GPIO_Pin_6|GPIO_Pin_7;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_DOWN;
GPIO_Init(GPIOB, &GPIO_InitStructure);
// RCC_MCO1Config(RCC_MCO1Source_PLLCLK, RCC_MCO1Div_4);
//return;
/*
Horizontal timing
-----------------
*/
TimerPeriod = 2048;
Channel1Pulse = 144; /* HSYNC */
Channel2Pulse = 352; /* HSYNC + BACK PORCH */
TIM_TimeBaseStructure.TIM_Prescaler = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseStructure.TIM_Period = TimerPeriod;
TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV2;
TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;
TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable;
TIM_OCInitStructure.TIM_Pulse = Channel1Pulse;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low;
TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_High;
TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Reset;
TIM_OCInitStructure.TIM_OCNIdleState = TIM_OCIdleState_Set;
TIM_OC1Init(TIM1, &TIM_OCInitStructure);
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_Inactive;
TIM_OCInitStructure.TIM_Pulse = Channel2Pulse;
TIM_OC2Init(TIM1, &TIM_OCInitStructure);
/* TIM1 counter enable and output enable */
TIM_CtrlPWMOutputs(TIM1, ENABLE);
/* Select TIM1 as Master */
TIM_SelectMasterSlaveMode(TIM1, TIM_MasterSlaveMode_Enable);
TIM_SelectOutputTrigger(TIM1, TIM_TRGOSource_Update);
/*
Vertical timing
---------------
*/
/* VSYNC (TIM2_CH2) and VSYNC_BACKPORCH (TIM2_CH3) */
/* Channel 2 and 3 Configuration in PWM mode */
TIM_SelectSlaveMode(TIM2, TIM_SlaveMode_Gated);
TIM_SelectInputTrigger(TIM2, TIM_TS_ITR0);
TimerPeriod =600;//625; /* Vertical lines */
Channel2Pulse = 2; /* Sync pulse */
Channel3Pulse = 24; /* Sync pulse + Back porch */
TIM_TimeBaseStructure.TIM_Prescaler = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseStructure.TIM_Period = TimerPeriod;
TIM_TimeBaseStructure.TIM_ClockDivision =2;
TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;
TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable;
TIM_OCInitStructure.TIM_Pulse = Channel2Pulse;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low;
TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_High;
TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Reset;
TIM_OCInitStructure.TIM_OCNIdleState = TIM_OCIdleState_Set;
TIM_OC2Init(TIM2, &TIM_OCInitStructure);
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_Inactive;
TIM_OCInitStructure.TIM_Pulse = Channel3Pulse;
TIM_OC3Init(TIM2, &TIM_OCInitStructure);
/* TIM2 counter enable and output enable */
TIM_CtrlPWMOutputs(TIM2, ENABLE);
/* Interrupt TIM2 */
nvic.NVIC_IRQChannel = TIM2_IRQn;
nvic.NVIC_IRQChannelPreemptionPriority = 0;
nvic.NVIC_IRQChannelSubPriority = 0;
nvic.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&nvic);
TIM_ITConfig(TIM2, TIM_IT_CC3, ENABLE);
/* Interrupt TIM1 */
nvic.NVIC_IRQChannel = TIM1_CC_IRQn;
nvic.NVIC_IRQChannelPreemptionPriority = 0;
nvic.NVIC_IRQChannelSubPriority = 0;
nvic.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&nvic);
TIM_ITConfig(TIM1, TIM_IT_CC2, ENABLE);
TIM_Cmd(TIM2, ENABLE);
TIM_Cmd(TIM1, ENABLE);
}為了提高速度，一開始使用了DMA傳輸畫素資料，但是，太快了，在行中斷後，DMA輸出的速度，經過多次嘗試無法控制在合理的時序內，導致顯示器識別的解析度過高，影象縮成一點點。最後還是放棄了，使用CPU迴圈將點陣輸出。
以下是電路圖：
以下是PCB
以下是實物圖和效果圖
可以當時鍾用
視訊連結：https://v.youku.com/v_show/id_XNDUzMzAyNDExMg==.html
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