Putting the U401, U421, and U451 to work
The U401⁄U421⁄U451 can be used for a wide range of applications, tying devices to the PC via USB. It is very simple to interface to the U401 using it as a large SIP-type of device in your custom application. Using the U401 to interface with SimmSticks couldn’t be easier. Like the U401, the U421 can also be used with solderless experimenter boards. The app notes located here in this section cover some of these potential applications.
- Digital output: Driving relays
Relays can be driven by the U401⁄U421 by setting the appropriate I⁄O lines to output and using appropriate relay driver circuitry. The Dontronics relay board DT205 is a simple way to accomplish this. The U451 has two onboard relays and 6 open collector outputs that can be used to drive more relays.
- Digital input: reading switches
Simple buttons, switches, and other CMOS-level inputs can be read by the U401⁄U421⁄U451. A Dontronics board, the DT203, can be used for input testing.
- Writing to an LCD display
Many character LCD modules (HD44780 devices) are compatible with the LCD commands of the U401⁄U421⁄U451. These modules range from one row of eight characters to four rows of forty characters.
- Expanding output by using SPI
A serial shift device, such as the 74HC595, allows for the expansion of output lines via the SPI port.
- Expanding input by using SPI
A parallel to serial device, such as the 74HC165, will increase the number of input lines by shifting eight inputs into the U401⁄U421⁄U451 via the SPI subsystem.
- Using the U401⁄U421⁄U451 as a power source
The U401⁄U421⁄U451 can be attached to a PC as a USB device and allow a circuit to use the 5V power from the USB port. There are examples of this in consumer devices, such as a notebook PC light.
- Serial A⁄D via SPI
A⁄D converters that interface via a SPI bus can be used to read analog values into the PC via the SPI subsystem of the U401⁄U421⁄U451.
- Parallel A⁄D via strobed byte read⁄write
Various microcontroller interface chips, such as some A⁄D converters, use a strobed read command to read eight bits of data. The strobe function of the U401⁄U421⁄U451 can interface to these chips.
- SPI EEPROM programming
SPI EEPROMS can be interfaced to the PC via the SPI subsystem of the U401⁄U421⁄U451. The EEPROM can be read and written using U401⁄U421⁄U451 commands.
- Atmel AVR (ATtiny) programming
The Atmel ATtiny series of microcontrollers can be programmed via the SPI subsystem of the U401⁄U421⁄U451.
- Serial potentiometer control
SPI potentiometers can be interfaced to and controlled by the U401⁄U421⁄U451.
- Home automation sensing and control
Door⁄window contacts can be monitored as inputs to the U401⁄U421⁄U451 and relays driven by outputs. Your home can be controlled by a PC interfaced to the U401⁄U421⁄U451. The U4x1 supports 1-wire⁄MicroLAN, often used in Home Automation for temperature sensing and remote I⁄O. The U451 with relays is especially suited to Home Automation.
- Model tethered robot or railroad control
Tethered robot experiments can be done with all of the features of the U401⁄U421⁄U451.
For more application information on interfacing components to I⁄O ports, check out books such as Jan Axelson’s Parallel Port Complete and The Microcontroller Idea Book. The interfacing ideas in these books can be extended to the U401⁄U421⁄U451.