I am trying to build a USB Bridge circuit as part of a larger project. What I mean by that is, I wish to control a parallel out circuit based on information transmitted by the host computer.
The idea behind the project is to have a USB powered Nixie Clock. A Nixie Display unit has a high operating voltage of about 150V. The power supply part of the project will take care of stepping up 5V DC (up to 500mA due to USB limit) to 150 V (Vdc), 5mA (0.75W).
We want our initial design to have no onboard clock circuitry, instead, we want the time and date information to come over a server lookup from the USB host computer.
Parallel Pin requirement:
Due to a power limitation, our design will rapidly switch between the 6 Nixie Tubes (HH MM SS) such that only one is lit up at a time. This is where the parallel out requirement stems from.
We need 6 pins to select the tube whose anode is pulled up to Vdc and 10 pins to choose the digit that currently glows. These final outputs can come from a decoder, but the system will still have 16 states.
So atleast 4 parallel pins are a requirement. However it would be better to have 3pins for tube control + 4 pins for digit control Since these will be interfaced to decoder ICs I believe, there is no significant current requirement for them.
A good solution could be to use a general purpose USB microcontroller such as the TUSB - 3210
However to keep things simpler, I have considered using a USB - UART interface chip such as the FTDI series of devices - FT232R (Single UART) and FT2232 (Dual UART, for more functional pins)
So what I want to be able to do is to program the pins available as per my will, without regard for their UART protocol functionality. I wish to avoid using the FT232R on-board EEPROM due to a lack of experience with using such programmers. This prevents me from using the control bus (CBUS) pins.
My questions about doing this are
- Is doing this a good idea, is it a common application of FT232R?
- I am on a tight power budget since I want to make a Nixie clock front end work using just USB power. Would the 3210 prove better for this application, considering the fact that USB controller will be a single package solution whereas a UART based solution would need some extra (Although low power) Decoder ICs?
Some useful information about the FT232R datasheet
- Page 7 - 10 pin functionality.
I am very new to big controller based projects, please provide feedback on how I could make the question better, provide more details...