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This project describes a transistor-based DIY FM transmitter with a range of 1/4 mile and adjustable transmitting frequency from 87-108 MHz. The author has also posted the PCB layout and the schematics of this project.
DIY FM transmitter
This electronic dashboard for a bicycle uses an Arduino and a few other parts to create a light control system and an LED speedometer. It is powered with eight 1.5V batteries connected in series. Six LEDs on the dashboard indicates how fast are you going on your bicycle.
Bicycle dashboard
STM32 micros just like any other micro provide hardware for serial communication. As we all know serial communication is a very important tool for debugging, connecting with external hardware like RFID, GPS, GSM modems, etc. and for performing other communication-related tasks. STM32s have several hardware serial (USART) ports. The number of ports available in a STM32 micro is dependent on device family type and the device itself. Typically there are at least 5 serial ports. Apart from the basic serial communication needs, STM32’s USART hardware also have support for LIN, one-wire, smart card protocols, SPI and IrDA. We can even utilize STM32’s DMA controller with USART hardware to achieve high speed automated data communication. Thus these hardware are truly universal synchronous-asynchronous receiver-transmitters.
In any standard serial communication, we need three wires – TX, RX and GND. TX pin is an output pin and transmits data serially to another device’s RX pin. RX pin is an input pin and is responsible for receiving data from another device’s TX pin. The two devices connected in this way must have same ground (GND). There are other pins like CTS and RTS which are used for hardware flow control. Additionally there’s also another pin called CK. It is transmitter’s clock output and used usually in SPI and other modes.
Depending on package, USART pins are arranged in the following pattern:
| BGA100 | LQFP100 | LQFP48 | LQFP64 | Pin Name | USART/UART |
| D9 | 67 | 29 | 41 | PA8 | USART1_CK |
| C10 | 70 | 32 | 44 | PA11 | USART1_CTS |
| B10 | 71 | 33 | 45 | PA12 | USART1_RTS |
| C9 | 68 | 30 | 42 | PA9 | USART1_TX |
| D10 | 69 | 31 | 43 | PA10 | USART1_RX |
| G3 | 29 | 14 | 20 | PA4 | USART2_CK |
| G2 | 23 | 10 | 14 | PA0 | USART2_CTS |
| H2 | 24 | 11 | 15 | PA1 | USART2_RTS |
| J2 | 25 | 12 | 16 | PA2 | USART2_TX |
| K2 | 26 | 13 | 17 | PA3 | USART2_RX |
| K8 | 51 | 25 | 33 | PB12 | USART3_CK |
| J8 | 52 | 26 | 34 | PB13 | USART3_CTS |
| H8 | 53 | 27 | 35 | PB14 | USART3_RTS |
| J7 | 47 | 21 | 29 | PB10 | USART3_TX |
| K7 | 48 | 22 | 30 | PB11 | USART3_RX |
| B8 | 79 | - | 52 | PC11 | UART4_RX |
| B9 | 78 | - | 51 | PC10 | UART4_TX |
| B7 | 83 | 54 | PD2 | UART5_RX | |
| C8 | 80 | - | 53 | PC12 | UART5_TX |
Personally I’m interested in LQFP packages, particularly 48 and 64 packages as they are mostly used in the most common STM32 development boards. I suggest locating USART/UART pins before working with them.
What is this Standard Peripheral Library (SPL)?
It’s just a collection of hardware libraries that provide an easy approach to any STM32 ARM programmer. It has support for every peripheral a STM32 micro has like CAN, USB, ADC, Timers, etc. In short it’s a hardware abstraction layer fully covering the STM32.
Why use the ST SPL?
Software Needed
Hardware Needed
How to use the Standard Peripheral Library?
First we need to prepare our MikroC PRO for ARM compiler for linking with SPL. I’m assuming that the compiler is preinstalled. First go to the compiler’s installation folder and look for the include folder. In my case, it is:
C:\Users\Public\Documents\Mikroelektronika\mikroC PRO for ARM\Include.
In this folder there’s a file named stdint.h. It’s basically a definition of variable types and other related stuffs. Rename it to stdint (backup).h and copy the new stdint.h file from the supplied folder to this location. We are done here.
Okay firstly the reason I wrote about the clock system instead of I/O ports or something else in this second post of the XMega series is simply because of the fact that without understanding clock configurations you won’t get what you want from your chip. Since XMega’s clock system is software-level configurable and complex at first, it makes itself the first priority module before anything else.
There are several clock sources that XMega micros can use as clock. These are both internal and external clock sources. As stated earlier, clocks are not set by fuse settings unlike traditional Mega AVRs, they are controlled by software and the outputs from these sources can be multiplied using the internal Phase Locked-Loop (PLL). Thus there’s a wide range of clocks available in the XMega and it’ll not be needed to shut down and reprogram the XMega just to change its clock – a great relief from meddling with fuse settings. Some port pins can also output the system clock frequency. Literally there’s no need to depend on external quartz crystals which are not available in all frequencies.
