Velleman K8055 - First Look

I went to "You Do It Electronics," the closest thing the Boston area has to a Fry's, and found that they had them. Fortunately, they had them marked incorrectly on their website, $29.90 rather than their normal $49.90, bonus for me as they gave me the website prices when I said that's why I came.

There is no official support for the device under Linux, there is, however, a fairly hackerish USB driver out there. It doesn't fully work, but it was close enough to take a good look. I should be releasing a cleaned up interface class on the site sooner or later.

By replacing "usb_interrupt_[read|write]" with "usb_bulk_[read|write]" I was able to get about 1200~1300 read-write cycles out of the unit. This will clearly make the LinuxPCRobot less bandwidth limited on I/O over the parallel port I2C. Also, since USB is handled in hardware, the communication between computer and device takes very little CPU.

The D2A circuit utilizes PWM. An analog signal is generated by a simple R/C circuit fed into an op/amp.

The A2D circuit utilizes a simple op/amp with programmable gain.

It uses a programmed PIC16C745 PIC chip with built in USB, PWM, and A2D converters.

It is clear that Velleman doesn't utilize all that this chip can do, but it is a pretty good start for short money.

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I've driven by this place a number of times but didn't know what they were. Thanks for the update.

Also, just in case anyone doesn't know what a Velleman K8055 is:

The K8055 interface board has 5 digital input channels and 8 digital output channels. In addition, there are two analogue inputs and two analogue outputs with 8 bit resolution. The number of inputs/outputs can be further expanded by connecting more (up to a maximum of four) cards to the PC's USB connectors. All communication routines are contained in a Dynamic Link Library (DLL). You may write custom Windows (98SE, 2000, Me, XP) applications in Delphi, Visual Basic, C++ Builder or any other 32-bit Windows application development tool that supports calls to a DLL.

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Thanks, Ken

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mlw wrote:

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Since I got such a great price, I bought two units. (Velleman K8055), and have them both running on a single USB hub, and both running, at the same time, are getting about 1200 I/Os a second. Not bad.

The % CPU load is about 2% per process.

AMD Athlon XP 2800+ running Kubuntu.

Not bad, there is very little impact on USB.

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