Ras_Mux

The Ras_Mux module is used in the CCD_Rasnik alignment monitoring system. It contains a video multiplexer and LED drivers. It is used to increase the number of alignment systems connected to a single computer.

Here the Ras_Mux for the demokit (1996) is described. If you want to know about the Ras_Mux for Atlas, go over here.

The electrical part of the system contains an LED and a black and white camera that is read out by means of a framegrabber. Typically the framegrabber is inserted in an IBM compatible PC. To be able to monitor more systems, a multiplexer is needed for the standard (RS170) video signals. Some framegrabbers have E.G. four multiplexed inputs. Also PC cards with 8 channel multiplexers are available.Since a camera can be part of multiple alignment monitoring systems, 2 LED drivers must be available for each video input. The two LEDs of such a system are labeled A and B. The LEDs must therefor be switched on and off. Commercially available interfaces could not fulfill our requirements, therefor the Ras_Mux was developed.

The basic module contains an 8 channel video multiplexer and 16 LED drivers. It is controlled via a Centronics port of a PC or any device that can generate a 7 bit dataword plus a strobe. The signals are TTL level. You can have a look at the block diagram.The system can be extended in two ways:

If the hard- and software of the system connected can handle 4 video inputs for example, one can connect 4 boards to it. These 4 boards are still controlled via a single port.
By adding a 5th Ras_Mux, one has a single video output.

A simple system can have up to 64 video inputs and a single output, by using 9 cards. It is controlled by a single LPT port. Further extensions are possible.

Several Ras_Mux crates have been build at NIKHEF. You can read more about what you need for a particular system.

Video

A single card has 8 video inputs and one buffered output. The system impedance is 75 ohms. Standard video signals are expected (RS170). You can have a look at some connection examples.

LED drivers

A card contains 16 LED drivers. They are divided into two groups: A and B. Addressing the LED is not fixed to the addressing of a video input.

You can read more about:

The LED drivers and power supply.
How to control a Ras_mux system.

Or you can have a look at:

The card layout.
A single module (75k GIF).
A 32 channel Ras_Mux crate (70k GIF).

Or go to CCD_Rasnik home page.

You can mail

suggestions for (or questions about) this page to: Henk Groenstege.

may 1999