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ozzytom

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Everything posted by ozzytom

  1. I just had a look at the specs of the USB-6008. A couple of things to be aware of. The digital outputs have an open drain configuration, meaning they can be configured to either source or sink current. If you want to see a voltage at the pin, you need to activate the internal pullup resistor. This will allow the port to come up to your internal USB voltage rail when activated. I thing the USB 6009 allows 3.3V as an option, but the USB 6008 only provides a 5V output. Have a look at pages 22~24 in the manual.... http://www.ni.com/pdf/manuals/371303k.pdf Bear in mind, that with the internal pullup you will only source about 1mA of drive with a 5V supply ( internal pullup is 4k7 ohms ) If using an external pullup, you are limited to 8.5mA max. Exceed this and run the risk of frying the I/O port. What relay are you intending to use. You said low current. What specifically? If you are using a solid state relay, you will be fine with some of the low input current devices. typically they only need a couple of mA input drive current. But if you are going to drive a coiled relay, it will have to have a coil resistance of greater than 600 ohms to limit the current below 8.5 mA. The coil should be positioned between the I/O pin, and the +5V supply. Disable the internal pullup, and use the relay coil resistance to limit the current. The relay will switch ON when the I/O port is LO, and will switch OFF when the I/O port is HI. Like I said, this is only OK if coil resistance is greater than 600 ohms. The higher the coil resistance, the lower the current that will flow (sink) into the I/O port. Best bet for reliability with coiled relays, is to use a buffer between the coil and the I/O port. A switching transistor would work well. By the way, relays are OK for slow switching, high voltage or high current loads.... but if you are switching low voltage DC circuits, you could use an opto isolator. They can be driven directly by the I/O port, and you can run a seperate (different voltage) circuit on the load side depending on specs of opto-isolator you choose. This way you have complete protection of your I/O port due to the isolation of the input circuit from the output circuit. cheers, tom
  2. G'day from the Land Down Under.... I only just found this forum.... and I've been a part time LabVIEW user since the Pioneer version almost 20 years ago. :headbang: I am a hardware engineer, and my position has evolved into a mechatronics role, incorportaing mechanical, electronic and computing systems. I love electronic hardware and mechanical design using tools such as Protel and Solidworks, and I used to love LabVIEW. I work in one of Australia's top sports institutes and have built equipment and developed apps using LabVIEW for research in sport science, determining the physiological parameters of elite athletes to help assess effectiveness of training and exercise protocols, and supplemental nutritional goods and other performance enhancement strategies (all the legal ones, that is ). Some of the applications include assessment of oxygen consumption (VO2), power output on various ergometers (cycling, rowing, kayak paddling), treadmill control and various force plate systems for biomechanics. Quality assurance has always been an important factor for our laboratory measurements, and I have developed quite a number of apps to evaluate the accuracy of our measurements. One such item is a dynamometer used to calibrate the ergometers we use... it is capable of delivering 2500 watts of power with a certified accuracy of +/- 0.05%. LabVIEW is used to control the dyno, as well as collect the data and provide the calibration reports. It was built 15 years ago and is still running reliably on a PC running Windows 95, with an ATMIO16 card, and some other custom hardware interfacing for isolation. ************************************************************************************************ My basic philosophy is, "If it ain't broke, don't fix it!" But I need to ascertain the ongoing viability of these apps, as new computers are introduced with new operating systems, and non-compatible bus architectures with my original design. All of the apps were developed using LabVIEW v5.1 and most of the apps use either the ATMIO16 multifunction acquisition card or PCTIO10 counter / timer card. I have been updating/upgrading PC hardware recently, and have succeeded in getting a couple of applications working using the newer M-series cards PCI-6024E, but I have issues of compatibility with several of my original apps using the AM9513 counter timing chip. I don't seem to be able to use the old style boards with LabVIEW 8 due to lack of driver support, and the new cards do not provide the same functionality of period measurement... or maybe I just don't know how to set them up. I have tried using the USB62XX series and can't get it done.... I am having some difficulty in making the transition from v5.1 to v8.2. It isn't as easy as I thought it should be. There are many incompatible vi's which make porting apps unsuccessful. I hope I might be able to get some assistance from all you full time LabVIEW gurus, and if there's anything an old fossil like me can help with, I'm only too happy to contribute. cheers tom
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