CCD_Rasnik straightness monitoring system
Description of the Ras_Mux module
This section describes the LED drivers and the
power supply .
LED drivers
A card contains 16 LED drivers. They are more or less related to a video input.
They are divided into two groups: A and B.
Addressing the LED is not fixed to the addressing of a video input.
The LED connections must not be connected to ground. A single LED driver can deliver 400 mA.
Not all LEDs can be switched on at the same time. In a group of four A and B outputs
(total 8 outputs), one LED can be switched on. So two outputs can be active on one card.
If the LED current does not exceed 200 mA, one can use the dual mode.
In that case one out of four outputs can be active, so four on a single card.
Dual mode is entered under software control.
The limitation of the number of LEDs, switched on at the same time,
is programmed in PALs (Programmable Array Logic).
Upon request, these can be altered to meet specific needs.
This can be useful, when the individual channels draw little current.
The A and B-LEDs share the positive supply line on the frontpanel connector.
An LED is connected between this positive power supply (18 V) and
an open collector driver with a 27 ohm series resistor.
How to control the LEDs.
The demo-kit lightsource connector.
Power supply
A Ras_Mux module requires a single power supply. On the PCB (printed
circuit board) a DC-DC converter takes care of generating plus and
minus 5 Volt. The current consumption of one board is app. 300 mA
from the +5V. The current drawn from the negative supply is neglectable.
The DC-DC convertor can deliver 850 mA. So three boards can be fed by
one convertor. There are screw terminals to interconnect the boards.
The input voltage can range from 9 to 36 Volts. The choice depends on
the requirements of the lightsource containing the LED. For the demo-kit
type of lightsource, 16 to 18V is a proper value.
Since the DC-DC convertor can consume 5 Watts at full load,
it may take up to app. 350 mA at 16 V. If only one board is used,
this would be app. 150 mA. The LEDs are fed directly
from the incoming power supply. This can be 4 times 100 mA E.G..
The power supply for the cameras is not an integral part of the system.
The choice depends on the requirements of the cameras connected.
Usually a camera draws something like 150 mA from the 12 Volt
power supply.
Something to keep in mind, when choosing a power supply for the cameras,
is the fact that many cameras contain a SMPS. This switched mode power
supply can draw considerable current when the input voltage is low.
This is the case when power is switched on. So if the nominal load
is close to the supply's maximum, it may never start.
The DC-DC convertor on the Ras_Mux board shows a simular problem.
Though a board, in a particular situation, may draw only 300 mA,
one may need a 1 A power supply.
In the Mux_Crate special provisions
have been made to ensure proper power-up of the Ras_Mux modules
and cameras. This module is known as the sequencer.
In the Ras_Mux crates it is located behind the
camera power panels.
Go to the
Ras_Mux home page or to the
CCD_Rasnik home page.
You can mail
suggestions for (or questions about) this page to:
Henk Groenstege.
july 1996