TTL To RS232 Converter
by Sidney Kantor
The Vision
Nothing too complicated here. I just wanted to be able to have my microcontroller communicate with my PC via the RS232 serial port. After some research I found a chip to do exactly what I needed and I designed and manufactured a board. The board worked well and I sold this single product online through my first company, M5 Control Systems. This was over 10 years ago. They sold for $14.95 and probably cost about $5 in parts. Profit margins were tight but I think I ended up selling almost 100 of these. Microcontollers operate at 0 to 3.3V or 0 to 5V and they communicate serially at these voltages as well with threshold voltages determined by whether they are TTL or CMOS. The PC's RS232 serial communication operates at +3 to +15V for logic level low and -3 to -15V for logic level high. So the board has to flip and scale the voltages so that the microcontroller can communicate with the PC.
My first PCB and product that I designed and manufactured from many years ago from my first company, M5 Control Systems. The TTL To RS232 Converter allows a microcontroller using TTL (Transistor Transistor Logic) to communicate with a PC using a standard serial cable and the RS232 serial COM port.