Instruction Manual. For EC-33 Geiger Computer Interface USB Hardware

Transcription

1 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. DAEDALON CORPORATION FAX (978) , daedalon@cove.com

2 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.

3 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 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

4 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 interchangeable 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

5 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: High Voltage: Warning Daedalon EN-01 or EN-04 tubes are recommended. Most end-window Geiger tubes can be used. 450 or 900 Vdc presets, V adjustable via front panel control. 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 Connections Indicators Controls The interface draws 5 Vdc directly from the computer s USB port. Current draw is 250mA max. Two Meter USB A to B cable. Dual colorcoded 4mm banana jacks for GM tube. Two panel LED lights for status and counting indications. Internal transducer for audio output of tube counts. AUDIO and GEIGER TUBE VOLTAGE slide switches on front panel. Front panel knob for adjusting voltage ( Vdc).

6 EC-33 Geiger Computer Interface USB 6 Dimensions Weight 4 H x 155 W x 175 D cm 350 g net System Requirements Windows: Macintosh: Windows 98, Windows 2000, or Windows XP. 5MB free memory, 1MB hard disk space. System 8.1(iMac), System 8.5, or later. Requires PowerPC processor, and USB port. SFS April 2004