Daedalon EC-33 User manual
DAEDALON CORPORATION
Instruction Manual
For
EC-33 Geiger Computer Interface USB
Hardware
Introduction
This interface is designed to connect to a computer’s USB (Universal Serial Bus)
port, power a Geiger tube, detect pulses, and send count rate information back
to the computer. The interface consists of a high voltage power supply to operate
a Geiger-Müeller tube and a microcontroller to communicate with the host
computer. The GM tube connects to the Interface via the color-coded 4 mm
banana jacks located on the rear panel.
The interface connects to the computer USB port with the supplied 2 m cable.
Since all power for the Interface is derived from the host computer’s USB port,
there is no need for batteries or power cables.
The high voltage Geiger tube power supply has preset outputs at 450 and 900
Volts. A third setting allows the output to be adjusted between 0 and 1200
Volts. An analog to digital converter reads the tube voltage, which is sent back
to the host computer along with count information. This is useful in developing
count rate vs. voltage plots to determine the plateau range for the tube.
The “STATUS” of the Interface is indicated by two pilot lights on the panel. The
“STATUS” will initially light up red to indicate the device is receiving power. Its
color will be yellow when the Interface has been recognized by the computer,
and green while software is collecting data.
The “COUNT” LED flashes when a pulse has been detected from the GM tube.
This is particularly helpful in verifying that the device is receiving counts from
the source. Software problems can be separated from hardware problems by
observing this indicator. The Interface also includes an audible transducer
producing a chirp for each event. This feature may be disabled via a rear panel
switch.
The Daedalon EC-33 Geiger Computer Interface has been designed to work with
the Windows operating system, as well as Macintosh computers.
EC-33 Geiger Computer Interface USB 2
Setup
It is possible to verify that the interface is working before installing software.
Installation will depend on which operating system you are using.
1. If installation is taking place on a computer running
Microsoft Windows 98 or Windows ME, locate your
installation disk. It does not need to be the original
CD used for installation.
2. Connect GM tube to the interface via the red and
black jacks on the rear panel.
CAUTION: To avoid possible electrical shock or damage to the interface,
connect the GM tube before connecting to the USB port on the computer.
3. Set the voltage selector switch to either 450 or 900
Volts as appropriate for the tube being used. An EN-
01 requires 450 Vdc and the EN-04 operates on 900
Vdc . If a different, non-standard voltage tube is
being used, set the Voltage selector switch to
“ADJUST” and turn the Voltage control fully
counterclockwise.
4. Locate the computer’s USB port. If a USB hub is
being used, it must be self-powered (i.e. with its own
external power supply). Connect the interface to the
computer using the supplied cable.
5. The “STATUS” LED should immediately turn red.
What happens next depends on the operating system
you are using:
Macintosh: The computer will automatically recognize the Interface and, after a
short delay, the light will change color to yellow. Sometimes the color change
from red to yellow is very fast, sometimes it might take a second or two. If the
LED does not turn yellow within a few seconds, see Troubleshooting. Otherwise,
proceed to step 7.
Windows 2000/XP: When the interface is first plugged in, the computer will
briefly display a message indicating that a new device was found. No user
intervention is required. The computer will automatically recognize the Interface,
and after a short delay, the light will change color to yellow. Sometimes the
color change from red to yellow is very fast, sometimes it might take a second or
two. If the LED does not turn yellow within a few seconds, see Troubleshooting.
Otherwise, proceed to step 7.
Windows 98/ME: The computer will recognize that you have plugged in a
“Human Interface Device” and starts the Add New Hardware Wizard. The driver
used for this device is included with Windows.
Click Next when this dialog appears:
When the following dialog appears, select “Search for the best driver for your
device”, then click Next.
EC-33 Geiger Computer Interface USB 3
Place the Windows distribution CD in the CD-ROM drive, and select CD-ROM
drive when the following dialog appears. If the Windows distribution CD is not
available, it is possible that the driver is in the default location suggested by the
“Specify Location” selection:
Click Next when the following dialog appears:
If all is well, Windows reports back with the following dialog box. If the
“STATUS” light is still red, try disconnecting, then reconnecting the interface. If
the LED does not turn yellow within a few seconds, see Troubleshooting.
6. With Windows 98/ME, this procedure may need to
be repeated for every USB port on the computer. It
would be worthwhile repeating step 5 for each port
now.
7. The “COUNTS” LED should flash whenever the GM
tube detects an ionizing particle. If the rear panel
switch is on, there will be a short audible beep for
every detected event as well. This verifies operation
of the tube and Interface.
Installation of the EC-33 Geiger Computer Interface is now complete. See the
software manual, (Windows or Macintosh), for details on software installation
and operation.
Hardware Description
The EC-33 connects to a computer via its USB port. It is a low speed device,
compliant with Version 1.1 of the USB specification. It will operate with any
USB port that meets version 1.0 or newer of the USB specification as defined by
the USB Implementers Forum. Power is drawn directly from the USB port, with
a maximum of 250 mA.
The Interface contains a regulated switching power supply to generate the high
voltage required for Geiger-Müeller tubes. Two fixed voltage presets provide
outputs of 500 Vdc and 900 Vdc, adequate for most GM tubes. A third setting
allows continuous adjustment of voltage from 0-1200 Vdc via a front panel
control.
Counts generated by the Geiger tube are generally on the order of tens of
microseconds. The pulse widths are stretched to 20 ms, so that the counts LED
is visible to the human eye. This stretched pulse controls the audible
transducer as well.
Counts from the tube are collected by the on-board microcontroller during 20
ms intervals, then sent back to the computer. The microcontroller clock is
synchronized with the USB timing, which in turn is controlled by a crystal inside
the host computer.
An 8-bit integer received by the computer represents the counts collected during
the measurement interval. Note that the limit for an 8 bit integer is 255. This
limit is more than sufficient, as the counting rate required to exceed this
EC-33 Geiger Computer Interface USB 4
number is so high that it would cause pileup and damage the Geiger tube (as
well as the experimenter!)
An 8 bit analog to digital converter measures voltage. One measurement is
taken every 20 ms and included in the packet that contains counts. Host
software displays a number taken by averaging 50 measurements, thus yielding
a higher effective resolution.
Dead time for a Geiger Counter is defined as a period of time for which the
counter will miss counts during each measurement interval. Dead time for the
counter is less than 2 microseconds, although if a pulse transition occurs
during this brief interval, it is still captured by the microcontroller. Pulse widths
coming from the Geiger tube are much longer than 2 microseconds, thus
effective dead time is zero.
Communication on the USB is very robust. The electrical design of the interface
is very conservative, using differential signaling. In addition, handshaking and
CRC error checking are built into the protocol. If data were to be corrupted
during transmission, the packet will be sent again to the host.
If the host computer goes into suspend mode (sometimes called standby or sleep
mode), the EC-33 will go into a very low power mode where it draws less than
500 µA. When the computer is reactivated, the Interface wakes up, and is ready
for use.
Troubleshooting
If the Interface “STATUS” light is not yellow after plugging it in, here are some
tips to try and uncover the problem.
1. Be sure that the computer is running Windows 98, or
Windows 2000, or newer. USB support in Windows
95 is not complete, and there is no USB support in
Windows NT.
2. If the Interface is connected to a hub, be sure it is a
self-powered hub, and that the power cable is
plugged into it properly. Most hubs will operate as
self-powered or bus powered depending on whether
the A/C adaptor is connected. Devices that appear
to be USB “splitters” are, in fact, bus powered hubs,
and the Geiger Interface will not work with them.
3. Determine whether other USB peripherals will work
on the current machine. A mouse or keyboard may
be borrowed from another machine and connected
for testing. USB keyboards and mice are inter-
changeable across platforms, so a Macintosh USB
mouse may be used on a PC and vice-versa.
4. If another known-good peripheral does not work on
this computer, it may be necessary to use the
Windows Device Manager to find out why. Look for a
device category called “Universal Serial Bus
EC-33 Geiger Computer Interface USB 5
Controllers”, and check to be sure that this is
activated and functioning correctly.
5. If there is no entry for the USB controller in the
Device Manager, be sure that the USB controller is
enabled at the BIOS level for the computer. Be sure
that any device drivers relevant to the USB controller
have been installed. A customer support website for
a computer manufacturer will generally provide both
advice and updated device drivers.
6. Try another USB cable. Avoid using cables longer
than 2 meters.
7. If it is possible to operate other USB peripherals on
the computer but the Daedalon Interface will not
work, try installing the Interface on a different
computer. Contact Daedalon customer support and
provide as much information as possible.
Specifications
Counting
Geiger Tube: Daedalon EN-01 or EN-04 tubes are
recommended. Most end-window Geiger
tubes can be used.
High Voltage: 450 or 900 Vdc presets, 0-1200V adjustable
via front panel control.
Warning Excessive voltage indicated by continuous
glow of the "COUNTING" light with no
source present. This rapidly wears out the
GM tube and must be avoided. Voltage
may be read from the interface using
provided software.
General
Power The interface draws 5 Vdc directly from the
computer’s USB port. Current draw is
250mA max.
Connections Two Meter USB ‘A’ to ‘B’ cable. Dual color-
coded 4mm banana jacks for GM tube.
Indicators Two panel LED lights for status and
counting indications. Internal transducer for
audio output of tube counts.
Controls AUDIO and GEIGER TUBE VOLTAGE slide
switches on front panel. Front panel knob
for adjusting voltage (0-1200 Vdc).
EC-33 Geiger Computer Interface USB 6
Dimensions 4 H x 155 W x 175 D cm
Weight 350 g net
System Requirements
Windows: Windows 98, Windows 2000, or Windows
XP. 5MB free memory, 1MB hard disk
space.
Macintosh: System 8.1(iMac), System 8.5, or later.
Requires PowerPC processor, and USB port.
SFS April 2004
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