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A development board with a software-defined USB interface

AVR drives USB

A development board with a software-defined USB interface
Is it possible to use a microcontroller from the pre-USB era to fashion a USB device without using additional ICs? The designers set themselves this question a while ago. Many long evenings later, the answer proved to be ‘yes’. As a result, we can now present a USB I/O board based on a standard AVR microcontroller – without any special USB chips!
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Resistors
R1 = 4kΩ7
R2,R5 = 1kΩ
R3 = SIL array 8x 100kΩ

R2,R4,R5 = 1kΩ5
R6,R7 = 68Ω
R8 = 10kΩ
R9 = SIL array 8x 470Ω
R10 = 100Ωk
P1 = 10kΩ preset
Capacitors
C1 = 22µF 20V radial
C2,C4,C5,C6,C7 = 100nF
C3 = 47µF 20V radial
C8,C9 = 18pF
Semiconductors
D1 = 1N4001
D2-D11 = low-current LED, red, lead pitch 2.5mm
IC1 = 7805CP
IC2 = DS1820
IC3 = ATmega32-16PC (programmed, E-SHOP # 060276-41)
IC4 = ULN2803A
Miscellaneous
K1= 2.5mm mains adaptor socket
K2= 10-way PCB terminal block, lead pitch 2.54 mm (e.g. Phoenix contact # 1725737)
K3= USB-B connector
K4 = 10-way boxheader
K5= 14-way pinheader
K6-K10= 3-way PCB terminal block, lead pitch 2.54mm (e.g. Phoenix contact # 1725669)
Re1-Re5 = 5V relay (e.g. OMRON G5V-1-DC5)
S1-S6 = pushbutton (e.g. OMRON B3F-1002)
X1 = 12MHz quartz crystal, HC49/U case
LCD module, 2x16 characters
PCB, E-SHOP # 060276-1

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