All microcontroller developers for debugging and device control use serial communication via a computer (or other device). The most commonly used serial communication is RS232. Ten years ago, every computer was equipped with a serial port, but today it is uncommon on PC platforms and almost non-existent in laptops.
As a solution for these problems, USB to Serial adapters was appeared. Unfortunately, not all adapters were proved to be useful. Problems with drivers and incompatibilities are the most common problems. Otherwise, these adapters are quite expensive considering that the small dimensions PCBs with only a few components. Prices on Amazon are about 15 dollars and more.
The most popular USB to Serial adapters are based on the FTDI chip. Manufactured by FTDI (www.ftdichip.com) specializes in manufacturing chips in converting peripherals to USB and has 20 years experience in this field. If you buy a device or create your own device based on FTDI chip, their site contains all the necessary drivers and software for chip configuration.
On this occasion, we will show you how to work with the chip from the series labeled as FTD232RL. Detailed instructions can be downloaded from manufacturer's website. Easiest way is by clicking HERE.
What should you know about this chip? If you want to make a USB to serial converter, follow our scheme. If you need something special, read the instructions.
This series has a built-in EPROM memory, which can be configured. Configuration can change the function of pins CBUS0..CBUS4 and some other things that we will explain later. The following table shows possible features of configurable pins. We will use CBUS0 and CBUS1 to drive LEDs for indication of changes TXD and RXD signal lines, and this is default function of this pins when you buy chip.
Our idea was to make a USB to serial converter. But in practice we often needed a way to connect directly to the microcontroller without a level converter (MAX232). The idea is to use the jumpers for the adjustment of the converter operation. Since the use of microcontrollers with a 3.3V supply voltage increased, the internal LDO (low drop out) voltage regulator build in chip was used to generate the appropriate voltage levels for the TxD and RxD signal lines. Jumpers are used to select appropriate level of signal lines. Detailed schematic is shown on picture.
Whole device is supplied from USB port. Also, it is possible to supply other devices through connector, but only with current that will not trigger protection build in inside USB port. Typically this current cannot exceed 100mA, but with configuration software can be set to maximum of 500mA.
For configuration of EPROM memory MProg 3.5 software is used. You can download software HERE. As you can see on picture, you can configure lot of FTDI chip, you can set maximum current that device can drain, even you can change a name that will be shown when device is connect to PC (or other platform) first time. When you make any changes on chip’s EPROM, device will be recognized on other COM port than last time, so don’t forget to adjust your Terminal software.
And at the end of the final look of the converter. FTDI chip is in bottom layer. If you want to make your own adapter, download shematic and PCB HERE. Note: In design it was used receptable DB9 connector, but you should know that male DB9 conector must be solder instead.