1Project Introduction

  The FM radio based on the RDA5807FP wireless transceiver chip has an operating voltage of 2.7~3.3V and can receive broadcasts in the 50~108MHz frequency band. Supports USB and battery power input , POWER is the power switch button , SEEK+/SEEK- are the electric tuning buttons , VOL+/VOL- are the volume control buttons , you can connect an external rod antenna and plug in headphones as antennas, and support dual-channel power amplifier and headphone audio output.

2 Chip principle

2.1 Internal structure

    The interior of RDA5807FP can be divided into two parts: analog and digital. The analog part includes a low-noise amplifier LNA that supports the FM band , an adjustable gain amplifier PGA , a voltage-controlled oscillator VCO , a high-precision analog-to-digital converter ADC , and a high-precision digital-to-analog converter. LDO for DAC and power supply ; the digital part includes audio processing DSP and digital interface. 

Figure 2-1 RDA5807FP internal structure block diagram

2.2 Pin description

The circuit symbol of     RDA5807FP is shown in Figure 2-2 . The package is SOP-16 . The pin definition and function description are shown in the table below.

Figure 2-2 Circuit symbol of RDA5807FP

3 Circuit Principle

  FM radio can be divided into three major modules: power input circuit, FM radio circuit and external audio output circuit. The circuit principles of each module will be analyzed below.

3.1 Power input circuit

 The power supply part mainly uses the Micro USB female socket as the power input port, C6/C7 as the power filter capacitor, 5V is then stepped down by a linear regulator to output 3.3V , which supplies power to the radio circuit, and C8/C9 is the stepped down filter capacitor ; You can also use the pin header to connect to an external 3.3V power supply .

Figure 3-1 Power input circuit

3.2 FM radio circuit

    The U1 wireless transceiver chip uses RDA5807FP to convert high-frequency signals into audio signals. Using the H1 rod antenna, J2 can use a headphone cable or a 3.5mm audio rod antenna as an antenna to receive signals . You can use a jumper cap to short pin J3 to switch the radio mode. Short-circuited to the power supply ( 1/2 short-circuited), the radio is in manual mode, you can switch channels through the SEEK+/SEEK- electric tuning button, short-circuited to ground ( 2/3 short-circuited), the radio is in automatic mode, write a program The radio is controlled through the I2C bus .

Figure 3-2 FM radio circuit

3.3 外接输出电路

  使用螺钉式接线端子P2/P3，可外接喇叭功放，输出左右双通道音频，也可以在J1采用耳机进行收听。

图3-3 外接输出电路

4 原理图设计

4.1 新建工程

  打开嘉立创EDA，创建工程并命名为【模拟电路】RDA5807FP调频收音机，将原理图文件命名为：SCH_RDA5807FP调频收音机。根据以下电路，划分为电源输入电路、调频收音电路、外接输出电路和M3铜柱接口四个板块进行电路原理图绘制。

图4-1 SCH_RDA5807FP调频收音机

4.2 器件选型

  在本项目的元器件选型中，USB连接器和LDO线性稳压器以及RDA5807FP芯片使用贴片封装，其他的元器件均选择插件即可，所有器件可直接在嘉立创EDA的元件库中进行搜索，如果对元器件不熟悉，也可以通过复制物料中的商品编号进行搜索（每一个元器件在立创商城都有唯一的商品编号），如果出现物料缺货情况，亦可选择其他可替换物料，通过以上电路的分析，相信聪明的你对各个元器件在电路中的作用有所了解，那么更换个别物料也不会影响到电路的工作性能的，了解电路工作特性后，电路选型也就变得简单了。

图4-2 元器件搜索示意图

图4-3 通过商品编号搜索示意图

4.3 物料清单

5 PCB设计

  完成原理图设计后，经过检查电路与网络连接正确后点击顶部菜单栏的 “设计 ”→ “原理图转PCB”（快捷键为Alt+P），随即会生成一个PCB设计界面，可先暂时忽略弹出的边框设置，然后将PCB文件保存到工程文件中，并命名为：PCB_RDA5807FP调频收音机。

5.1 边框设计

  在绘制PCB前需根据个人意愿以及元器件数量所占空间确定PCB的形状及边框大小，若无特殊外壳要求，一般设计成矩形、圆形以及正方形。在设计该项目时，秉承着大小合适，美观大方的原则，我们在顶部工具菜单栏下的边框设置选型中设定了一个长为70mm、宽50mm、圆角半径为2mm的圆角矩形。实际板框大小会随着布局布线中进行调整，如果太小可适当放大，太大也可缩小边框，风格样式可自由发挥，但尽量控制在10cm*10cm之内，这样就可以到嘉立创免费打样啦～

图5-1 边框设置

图5-2 RDA5807FP调频收音机边框示意图

5.2 PCB布局

  在绘制完板框外形后，接下来进行PCB设计的第二步，对元器件进行分类和布局，分类指的是按照电路原理图的功能模块把各个元器件进行分类，图中有很多按键和对外的接口，这里需要我们用到立创EDA所提供的布局传递功能，首先确保PCB工程已保存到原理图文件的同一个工程文件夹中，然后框选原理图中的某一电路模块，比如选中按键电路，然后点击顶部菜单栏中的 “工具” → “布局传递”（快捷键为Ctrl+Shift+X），PCB页面所对应的元器件就好进行选中并按照原理图布局进行摆放， 使用这个方法将各个电路模块进行分类后依次摆放在前面所放置的边框中。

  在布局的时候注意摆放整齐，可根据飞线的指引进行摆放，按照原理图信号的流向和器件连接关系进行摆放，是可以把原理图器件摆放非常整齐的，在布局的过程中注意接口位置，布局参考如图5-3所示。 在该项目的布局中提供以下几点参考建议：

（1）摆放元器件时应先按原理图摆放，再细调位置；

（2）在板边四个角分别放置M3铜柱孔，用于固定支撑，左上角孔与天线复用；

（3）天线座及电源输入放置在左侧板边，耳机座及喇叭音频接口放置在右侧板边；

（4）无源晶振靠近放置在RDA5807芯片附近；

（5）收音机五个功能按键排列等间距放置在下侧板边；

布局参考如图5-3所示，初次设计可参考下图进行布局，也可以自行合理摆放。

图5-3  PCB布局参考图（飞线已隐藏）

5.3 PCB走线

  接下来进行PCB设计的第三步：PCB走线，全称为印刷电路板布线（PCB LAYOUT）。由于电路板有顶面与底面两个面，在PCB走线也就可以分为顶层和底层走线，其中顶层走线默认是红色线，底层为蓝色线，也可按照个人喜好设置其他颜色，走线也就是在电路板中按照飞线连接导线，将相同的网络连接起来即可。

  首先选择层与元素中要走线的层，然后点击导线工具进行连线（快捷键为W）。看似简单的连连看，其中需要我们耐心的进行调整，元器件的摆放布局也会影响走线的难度，所以还需要在走线过程中进一步调整布局，进一步优化。前面所介绍的PCB布局相当于是在给走线做铺垫，布局好了，走线也就自然顺畅了。在该项目的走线中提供以下几点参考建议：

（1）电源线设置为25mil，信号线设置为15mil宽度；

（2）走线以顶层走线为主，走不通的可以切换到底层进行连接；

（3）走线过程中优先走直线，需要拐弯的地方以圆弧拐弯或钝角为主；

（4）最后加上泪滴，添加丝印标记该按键功能以及接口功能；

（5）将客户编号指定位置藏于耳机座下；

布线参考如图5-4所示，初次设计可参考下图进行走线，也可自由设计，属于你的调频收音机。

图5-4 PCB走线参考图

5.4 覆铜与丝印

    PCB 走线画完后进行覆铜，就可以连接好 GND 网络。丝印字符遵循从上往下从左到右的原则。对按键、音频接口和接线端子等加上丝印标注说明，在板子加上工程名称与LOGO。

图 5-5 PCB 顶层覆铜与丝印参考图

图 5-6 PCB 底层覆铜与丝印参考图

6Welding and Debugging

6.1 Hardware welding

  When welding, you should first weld the chip components, then the plug-in components, and follow the principle of welding from low to high. Novices can refer to the welding sequence: USB/LDO/RDA5807 → Crystal Oscillator / Diode → Resistor / Inductor → Capacitor / LED / Transistor → Row Pin / button→audio interface / terminal block.

  When welding, be careful not to have false soldering, missed soldering, or wrong soldering. For devices with polarity such as capacitors and diodes, you need to pay attention to the welding direction. All devices must be aligned and flat to avoid unevenness.

  When welding, the temperature must be controlled, and the temperature should not be too high. Too high a temperature can easily cause the device to burn out; the tin point should not be too large, as it can easily cause the device to be welded and have poor contact; do not use too much force, as too much force can easily cause the board to break or short circuit. The solder mask paint peels off, etc.

Figure 6-1 PCB assembly diagram

Figure 6-2   Unsoldered PCB board

6.2 Hardware debugging

  After the welding is completed, check the circuit for short circuits, open circuits, false soldering, etc. Only after the inspection is correct can you turn on the power. When using pin headers to connect external power supplies, you should pay attention to the positive and negative polarity of the power supply, and do not connect it reversely.

  Use a jumper cap to short-circuit J3 in manual mode. If you do not short-circuit J3 , you will not receive sound. Plug in the earphones to hear the rustling sound. Pull out the antenna and press SEEK+/SEEK- to receive the FM station. You can receive five to six A station.

Figure 6-3  PCB-3D preview

Figure 6-4 PCBA physical diagram

Figure 6-5 RDA5807 FM radio