(The D-Sub connector is female.)

Keywords: USB, LPT, parallel, parallel port, printer port, converter, adaptor

Converter from USB to parallel port (25 pin SubD receptacle) with hardware virtualization at input/output instruction level
Supports all parallel port modes named SPP, EPP and ECP, 16 Byte FIFO depth
USB Low Speed (1.5 Mbit/s signaling; 1 kByte/s for input/output instructions)
Supports USB suspend mode with reduced power consumption
Full open-source, even for schematics and PCBs

USB2LPT – Cloning instructions for Release 1.6

This device is almost the same as Release 1.5.
For high-speed USB, there is a Release 1.7.

If 3.3V operation of ATmega is wanted, a user can now populate a dual diode BAV199 instead of the LD1117 of the previous version. This enables drawing less than 500 µA of standby current in this case.

The firmware from december 2010 to february 2012 is not compatible to Windows Vista and Windows 7 (32 and 64 bit) – please update!

Electronic Components

You need:

Pieces	Description	Reichelt Order Code	Price in € (2007)
1	ATmega8 in TQFP32 package	ATMEGA 8-16 TQ	1.70
1	Ceramic capacitor 100 nF 0603	X7R-G0603 100n	0.051
1	Resistor array 220 Ω 1206	BCN16 220	0.02
1	Resistor 10 kΩ 0805	SMD-0805 10k	0.10
1	Electrolytic capacitor 10 µF	rad 10/35	0.041
1	Yellow LED 3 mm	LED 3mm ge	0.051
1	SubD receptacle 25 pin	D-SUB BU 25	0.15
1	USB receptacle MiniB through-hole	USB BWM	0.50
1	Housing	Kappe CG25G	0.13
1	USB cable 1 m	AK 673-A	0.98
1	Two-sided PCB (see below)	UL16LP	1.00

It's not hard to populate this PCB.

Photo upper side Photo lower side
(Sufficiently) populated PCB

The LED

The yellow multi-function LED shows following states:

off:
- No power supply (cable broken or similar)
- USB2LPT not recognized by computer
- USB Standby mode - e.g. at notebook's suspend mode
- USB2LPT in bootloader mode
on:
- USB2LPT active, output drivers enabled, inputs with pull-up resistors
flashing:
- fast: USB BULK or INTERRUPT transfers (redirected IN and OUT instructions; normal operation)
- slow: USB CONTROL transfers (mostly initiated by Windows)

Software

Schematic and PCB, Source
For Windows driver and AVR firmware, see page above, and how-to-use instructions.
Here you can browse the firmware source in your web browser.

Here are some notes about firmware implementation:

The current USB2LPT Low-Speed (1.6) firmware implementation has many ways for I/O transaction. However, the driver (usb2lpt.sys) preferes only one, the oldest and still fastest way, using two BULK pipes. One BULK OUT for addresses and output (write) data, another BULK IN for input (read) data. Refer to DeviceIoControl() based API for understanding.
The other ways for I/O transactions exist for following reasons:

The very simple and low-performance EP0 based for one Linux user (Henning Paul). Contrary to all other interfaces, it has no ECP/EPP support at all.
I never used this interface.

The INTERRUPT OUT + IN alternative for Linux, Vista, Win7 to conform to USB standard which forbids BULK for low-speed USB devices. (USB2LPT was developed for full-speed AN2313 controller.) The device is preconfigured to use INTERRUPT instead of BULK. This works on all known systems but is at least 8 times slower than BULK. Activating BULK will remove that slowdown but will render the entire device as defective in Windows Vista, 7, 8, and newer, and Linux.
The usb2lpt.sys driver supports both BULK and INTERRUPT pipes.

The advanced EP0 based as a faster alternative to INTERRUPT pipes.
The driver currently doesn't use this way, but it's planned.

The HID (Human Interface Device) way to overcome the driver certification trouble on Win64 systems.
The driver cannot use this way because Windows loads its generic HID driver for this interface (that omits certification hassle). This interface is for USB2LPT-adopted inpout32.dll and similar port access libraries. Note that most parallel port accessing software will not run on 64 bit systems, even with a true parallel port. In such cases, requiring to use InpOut32.dll is not a limitation.

Preparations

Drill holes into SubD shell for LED
Label the shell
Bend pins of USB receptacle straight – see picture
Trim pins of LED and electrolytic capacitor to about 1 cm length
Download and install either PonyProg or WinAVR
PonyProg: Setup interface as shown here, check by connecting the programming adapter (this checks for connection between Pin 2 and Pin 12), invoke Setup→Calibration

Making-Of

New: The do-it-yourself process for the similar 1.7 version is available at YouTube! (Three parts, running time ca. 30 minutes, German comments, English subtitling)

Solder paste applying, SMD population
SMD population (cont.), Reflow process, SubD receptacle
USB receptacle, LED, Housing shell, Final check

put SMD cream, 4 SMD components, make a reflow process – or solder by hand
Check for short circuit between 5 volts and ground
press and solder SubD receptacle keeping ½ mm gap between PCB and SubD shroud
Align and solder USB receptacle (see helper tool), solder the pins with lowest possible iron temperature
Populate electrolytic capacitor as flat as possible
Align and solder the LED using the shell, watch for right polarity
Check for short circuit between 5 volts and ground again
Check “operation” by connecting the USB cable, must show as “inoperational USB device”, this is the power supply for programming the bootloader
Connect programming adapter to an old-style parallel port and program the bootloader, either
- PonyProg: load main.hex, write, set fuses exactly as shown here
  Do not twiddle with the fuses without knowledge! You may make the ATmega unaccessible to PonyProg and all other low-voltage serial programmers!
  or
- WinAVR: invoke make prog (directory src/firmware/USB2LPT6/bootloadHID)
If your programming software doesn't recognize the right controller, check:
- Programming adapter soldered correctly?
- Programming adapter used in correct direction?
- Solder jumper SJ2 (still) connected?
- Pins of SubD25 socket soldered correctly?
- Microcontroller soldered in correct alignment and angle? (If wrong, remove with a hot-air gun. If 180° wrong, use new ATmega8.)
- Mikrocontroller soldered without shorts?
Cycle power to USB2LPT, let install driver usb2lpt.inf. The Bootloader ( HIDboot) will not occur because the .hex file above contains both bootloader and the real USB2LPT firmware.
If there is no USB2LPT, then check:
- Solder joints on USB socket correctly?
- USB socket not melted? (Contact springs still visible?)
- SMD solder joints correctly without shorts?
Check with another computer and/or with front-side or back-side USB connectors on PC, or using a USB hub. If USB2LPT seems to work unreliable, populating the crystal and downgrading to USB2LPT 1.5 firmware may help. The reason is an unstable 5V supply, that jitters the internal RC oscillator of the 1.6 firmware solution.
Remove programming adapter
Scratch jumper SJ2 (the only solder jumper on silk-screen-less lower PCB side)
Connect LPT checker or similar device, run Kurzschlusstest.exe, make corrections if necessary
Alternatively, download fw-utils.en.zip first for English message utilities (it's not supported by me).
Close shell, make a final check

Known PCB bugs

The crystal and the both 22 pF capacitors are not to populate
Population with ATmegaX8 is currently not recommended.
If you want ATmega48 population, R₁ should be 4.7 kΩ, and the older firmware USB2LPT5 (and crystal) must be used. A bootloader cannot be used (this chip has no bootloader support)
If D₂ (BAV199) is used, R₁ must be 1.5 kΩ
The 5 V USB interface with 220 Ω series resistors is incompatible to some notebooks. In such a case, the device will not be recognized correctly, and you see „Unknown device“. No driver installation will help here, and any force may damage your Windows installation.
Possible solutions:
- Use a USB hub in between, or an active extension cable (which is essentially a one-port hub).
- Change components to 3.3 V design, i.e. populate the BAV199 as stated above. Of course, this will result in 3.3 V I/O voltages, and the inputs are then not truly 5.0 V compliant.
- Populate flying 3.9 V zener diodes to USB D+ and D- wires.

Solder jumpers

This revision 6 (USB2LPT 1.6) has 3 pre-connected solder jumpers:

SJ1 can assign power to pin 25 of SubD receptacle:
- open: Pin 25 unbeschaltet
- right connected: Pin 25 to ground (default)
- left connected: Pin 25 to 5 volts
If power is needed, populating a self-resetting fuse is highly recommended.
SJ2, connected at PCB fabrication, scratched at device manufacturing: activates the RESET pin of ATmega for programming the microcontroller.
SJ3, connected by default, scratch when you want 3.3 volts operation of ATmega8 (e.g. for safer JTAG connection), populate a BAV199 and change R₁. Moreover, scatch it to measure device's current consumption and re-solder.