Converter From USB To Parallel

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
To USB2LPT — Overview

USB2LPT – Cloning instructions for Release 1.5

This device was built using AVRUSB firmware developed by Objective Development.

Meanwhile, a very similar Release 1.6 exists.

This Low-Speed device violates following USB specification rules:

Detachable cable (must be captive for Low-Speed)

Output drivers with 5 V (must be 3.3 V, but USB is 5 V tolerant)

No differential data input (only one line D- is sampled)

No data clock regenration while receiving (only at packet start)

No error detection of input data (OUT direction), no time for CRC16

Data transfer using BULK pipes (not specified for low-speed, but works on Windows – for Linux there is an "Alternate Setting" with INTERRUPT pipes instead)

However, new to this firmware, following rules are accepted:

Suspend detection and lowered suspend current (below 500 µA)

Electronic Components

You need:

Pieces	Description	Reichelt Order Code	Price in € (2007)
1	ATmega8 in TQFP32 package or ATmega48	ATMEGA 8-16 TQ ATMEGA 48-20 AU	1,70 1,45
1	Crystal 12000 kHz	12,0000-HC49U-S	0,24
1	Electrolytic capacitor 10 µF	rad 10/35	0,041
1	USB receptacle MiniB through-hole	USB BWM	0,50
1	SubD receptacle 25 pin	D-SUB BU 25	0,15
1	Yellow LED 3 mm	LED 3mm ST ge	0,051
1	Resistor array 220Ω	BCN16	0,02
2	Ceramic capacitor 22 pF 0603	NPO-G0603 22p	0,051
1	Ceramic capacitor 100 nF 0603	X7R-G0603 100n	0,051
1	Resistor 10 kΩ 0805 or 4.7 kΩ for ATmega48	SMD-0805 10k SMD-0805 4,70k	0,10
1	Housing	Kappe CG25G	0,13
1	USB cable 1 m	AK 673-A	0,98
1	Two-sided PCB (see below)	UL-15	5,00

populated PCB photo — (Sufficiently) populated PCB

Software

Schematic and PCB, Source , Programming Interface: Wiring
That's right, my USB2LPT5 only needs two port pins for USB, no additional INT pin. I use the Input Capture interrupt of Timer1. As a side effect, I can exactly measure the time between two SOFs.
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.

Known PCB bugs

R₂ must be 10 kΩ or at least 4.7 kΩ for right voltages on USB!
1.5 kΩ is only suitable for 3.3V operation using LD1117

Solder Jumper

This revision 5 (USB2LPT 1.5) has three solder jumpers:

SJ1 connects pin 25 of SubD receptacle:
- open: to nothing (free pin)
- right shorted: to ground (default)
- left shorted: to 5 Volt
SJ2, shorted by default, cut at delivery: Activation of RESET pin for programming the ATmega chip.
SJ3, shorted by default, for optional 3.3 Volt regulator, or for measuring power consumption.