About the article

USB/I²C interface

I-square-C rules...

USB/I²C interface
Since the introduction of the I2C bus in the eighties by Philips it has been used many times to provide a simple connection between a PC and home-built circuits. This often made use of a simple interface connected to the parallel port of the PC. This now seems a bit dated, so we’ve designed a USB/I2C interface for you to build.Articles about the I2C bus have appeared several times in Elektor Electronics. We have even published designs for a whole range of modules that communicated with a PC via the I2C bus. At that time we used an ISA card to provide an I2C interface. Another type of interface that was frequently used was a simple circuit that connected to the parallel port.But with the introduction of modern operating systems it became much more difficult to control the parallel port correctly. The old software would often no longer function properly.We have designed a new I2C interface, which uses the USB bus instead of the parallel port to connect to the PC, so that it can be easily used with newer PCs and modern operating systems.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD 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.

Extra info / Update
In Figures 2 and 4, the inputs and outputs of IC1 have been transposed. In both diagrams, pins 2 and 3, and 6 and 7, should be swapped over.

In the circuit diagram in Figure 1, the outer connection of the mains adapter socket is shown connected to ground while the centre pin carries the positive supply voltage. On the PCB designed for the project, these connections are the other way around.

Even if the circuit diagram does not show it explicitly, the P82B715PN is a bidirectional component (see www.semiconductors.philips.com/pip/P82B715PN.html). Consequently, nothing changes when compared to the circuit without the P82B715PN. Incidentally, controlling devices over the I2C bus always requires a bidirectional interface.
Component list
R1 = 15kOhm
R2,R3 = 33Ohm
R4 = 1kOhm5
R5,R6,R8,R9,R10 = 10kOhm
R7 = 5kOhm6
R11,R12 = 330Ohm
C1,C4 = 1µ F 16V radial
C2,C3,C7-C11 = 100nF
C5,C6 = 22pF
D1,D2 = BAT85
D3 = 1N4001
IC1 = TUSB3410 (Digikey # 296-12699-ND)
IC2 = 24LC64, programmed, order code 040334-21
IC3 = LM1117-3.3 or LD1117V33C (Digikey # 497-1492-5-ND)
IC4 =7805
IC5 = P82B715PN (Farnell # 559-258; RS Components # 821-784)
T1,T2 = FDV301N (Farnell # 995-848; RS Components # 354-4907)
K1 = USB-B connector, angled, PCB mount (Farnell # 152-754)
K2 = mains adapter socket PCB mount
K3 = 6-way RJ-11 connector (Farnell # 393-8359)
X1 = 12MHz quartz crystal
USB cable
PCB, order code 040334-1 (see Readers Services page)
Disk, project software, order code 040334-11 or Free Download
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