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Velleman K8055 - [Velleman K8055]

Velleman K8055

What is the Velleman K8055 card?

Picture of a K8055 card

The Velleman K8055 is a computer interface card. It allows you to add any electrical equipment with it. Unlike with K8000 the K8055 uses USB to connect it to a computer. You can run it on any modern computer.

The card is way more limited than the K8000 card: it has less connections. It has 8 digital outputs, 5 digital inputs, 2 A/D inputs and 2 D/A or PWM outputs. You can connect up to 4 cards simultaneous.

Card Function

Schematic diagram of the K8055 circuit

Unlike the K8000 - which runs on the I2C protocol - the K8055 runs by a single PIC microcontroller: the PIC16C745. The code that runs on the PIC has not been made public by Velleman.

The digital inputs or outputs are not directly connected to the PIC: they are connected through an UNL2803 driver IC. This makes sure they are not directly connected to the microcontroller.

The analog inputs are connected trough two operational amplifiers: the TLV274. The attenuation can be regulated with a trimmer. Optionally you can add some resistors to the circuit to make the opamp amplify your analog signal. This can be used when you have a weak analog signal. I believe the opamps will also make sure the PIC is somewhat protected against over voltages on the A/D inputs.

The PIC has two PWM outputs (Pulse Width Modulation). They can be set to a certain frequency and duty cycle. The PWM outputs on the K8055 are available as open collector outputs (transistor BC337). According to its datasheet this transistor can switch currents up to 800 mA. Velleman however specifies the outputs may switch only 100 mA. It's best you add your own circuit if you want to have higher powered PWM outputs. The PWM outputs are converted to normal D/A outputs through an Opamp. So both PWM and DAC outputs share the same microcontroller pins.

Limitations

The K8055 is easy to connect and to use. But it is less protected than the K8000 which is optically isolated from the computer. K8000's I/O ports are isolated as well.

Copyright ©1998-2017 Vanderhaegen Bart - last modified: August 24, 2013