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Everything posted by Olihou

  1. At last I have been able to find locally a supply of UV sensor diodes OS100 from Orion Semiconductor: http://www.orion-semi.com/orionsemi.html I have tried it out, giving a few mV output when shined with a small UV lamp used for checking bank notes. Will look for suitable circuits to make a handy UVB Meter. Again any advice please with regard to the circuits, the curent amplifiers....and how to calibrate it evetually ....... ?????
  2. Thanks OnOff. 6490 is probably OK for my application, except I am not sure how its unit :Index has been defined. I would prefer the unit uW/cm2. Besides, being a module with the amplifier the price will probably be high. I would prefer having a sensor diode and build the circuit my self. It saves money and it is fun in building something to one's own desire. Any one with other recommendations please ? :D
  3. I have the interest to build a UVB meter for measuring the ultraviolet radiation intensity in the wavelength range from 280 to 320 nanometer. It will be used in my reptile house. The reptiles need UVB light for making vitamin D for bone health, but over doze will hurt them. UV meters are available as laboratory instruments and are quite expensive (hundreds of dollars). I think I can meet my target with a simple circuit. What I need is a UVB detector diode plus a high gain current amplifier. May be a budget of $50 will suffice? Any advice please, on the detector diodes and circuits? :D
  4. Hello Jedi As an amateur I have the interesrt in building an ECG machine, and have now completed the basic amplifier circuit to acquire the ECG signal from my own body. Please see my previous posting in this forum: http://www.electronics-lab.com/forum/index.php?topic=1746.0 What I like to do may be some what similar to what you are planing to do, i.e. to display the signal on the PC, for ease of data manupulation and storage, etc. I am a hardware man and I find it difficult to get the part of job in computer programming. I have used a program downloaded from the Internet to display the ECG signal fed to the PC via the sound card. However since a sound card is basically an AC amplifier, the DC content of the ECG signal is lost and so there is some sort of distortion introduced. I am still figuring out how this problem can be solved by software means. May be we can share our experience with each other. I am not familiar with medical equipment in practical use -- would it be easy nowadays to have readily available digital output from the ECG machines ? So why do you need the ADC input board for this purpose? Best regards, Olihou
  5. Hi Audioguru and every body I am curious at the thinking that kit-makers put errors in their products purposely -- and if the kits would not work -- would that defeat their intention to sell the kits -- so they have protected their intellectual properties -- but not their businesses ? I have experience in using kits only a few times and am lucky that I succeed every time. It is nice to have some one in this forum poiting out the traps, saving the headache of many .....
  6. Thanks Ante. I will try what you have recommended. I am now exploring Labview. I have already downloaded the program but it seems quite sophisticated that I need to spent some time to find out how it can be used. Oli
  7. Hello Lou How about this? See if it helps. http://www.national.com/an/AN/AN-30.pdf The log amplifier output gives a DB equivalent of the input voltage. An ADC would be required should you need the digital form. Oli
  8. Any one any advice please ? Just tell me if you are aware of any programme for Windows to convert a PC to a chart recorder -- Yes or no please? Oli
  9. Is the output you have in mind digital or analog? If just for analog, there are functional circuits using op amps and diodes, as far as I can recall. Have you search for it in the cyber?
  10. Your requirement is not very clear to most readers, I am afraid. Perhaps you can describe what your physics experiment is so that others will know what you really want. Also a block diagram of the circuit you like to have should help. Oli
  11. I have some experience in powering low power circuits directly from 220V mains, without the use of a power transformer. Voltage regulation could be achieved by the use of zener diodes Darrins needs to tell others what kind of device/circuit he/she intends to power before others can offer advice. It could be rather dangerous unless every thing is well insulated, by one with good experience in high voltage circuits. Oli
  12. Hi Does any one konw if there is any programme (preferrably free) for Windows to convert a PC to a chart recorder, using the audio card as the signal input? I have tried some programs for PC oscilloscope. However their time base is not long enough for recording signals for long time, say hours. I intend to have it for monitoring things like temparature variations. It will also be used for ECG. Thanks. Oli
  13. Hello dicky Dimming by a trim-pot? What do you mean? What do you want to do? Oli?
  14. They prices are in US$, and are quoted by Farnell in HK$297 and HK$79 respectively. It is expensive ! I think I will take Audioguru's advice and try the TL072 or other popular opamps first. However I can foresee that much circuit skill would be needed to get it perform, in say achieving good CMRR values. I have to do further searching for good circuit designs before switching on my soldering iron .... Cheers, Oli
  15. They prices are in US$, and are quoted by Farnell in HK$297 and HK$79 respectively. It is expensive ! I think I will take Audioguru's advice and try the TL072 or other popular opamps first. However I can foresee that much circuit skill would be needed to get it perform, in say achieving good CMRR values. I have to do further searching for good circuit designs before switching on my soldering iron .... Cheers, Oli
  16. Hi Audioguru Congratulations! You have made a good stuff again! By the way, I undersdtand that we have a university here conducting an R&D project on electronic stethoscope. It is said that the new device have many good features and would evetually replace the traditional mechanical ones .... This is an intersting as well as useful project ! :) Oli
  17. Thanks Trigger and Audioguru ! With your advice I have now been able to locate the suppliers locally. The AD624AD cost $38. The INA118PB costs $10. Surprisingly INA118PB seems to have better specifications! I will certainly use INA118PB! I just wonder if AD624 is something out of production? -- scarcity causes expensiveness .... Oli
  18. Dear Audioguru I am in a small place south of China, ruled by British for one hundred years until 1997 when it is returned to China. Got it? ;) I have been searching for the inamps. They are available locally only in large quantities! So I am still thinking if I can use opamps readily available, as you have suggested. However I find opamps, such as TL074, LM741 or LM709 are normally of low CMRR, around 20 to 30 DB lower than the inamps. Besides, to build inamps from these opamps, high matching resistors (specified to .1% in circuits I have seen) are needed. No easy job to me! Or you can advise me where to get the inamps. I will be prepared to buy just two to three pieces, as they seem to be very expensive. One more question for your help please. For the INA118 circuit I have posted previously, I do not quite understand what is the purpose of the amplifier output of which is connected via a 390 Kohm resistor to the right leg. Also why the gain is made to 39 (390k over 10 kohm)? Do you have a good explanation? The links you have provided to other discussion forum are very useful to me. Thanks and best regards Oli from Hong Kong
  19. Here is one circuit I have found from : Has any one tried it out? How good can it perform ? I would like to have some assurance of the circuit before trying to search for the parts, the op amps in particular, which seem to be unavailable locally. Will any one please advise. :o Oli
  20. Hi Audioguru Thanks for your advice. The only thing I do not understand is that why I should be wearing a white doctor's gown. ::) I have started searching for the instrumentation amp, but am not successful yet from local suppliers I have checked. I will continue to search for it. I do need help please!!! Can any one supply more complete circuits/guides for this project, please? ??? Oli
  21. Hi Audioguru Thank you very much for your advice. You have always been so nice and helpful. My interest in ECG arises from my curiosity, and most probably due to my childhood desire to become a medical doctor, but that has been only a dream for me. I just wish to find out if a ECG can reveal one's cardiovascular health. The commercial unit must be very expensive. I just wish to have a cheap and simple unit to show if there is some early indication of changes in the heart condition at home, whenever we want. Undoubtedly I have no intention to have it replacing an actual medical check. May be the circuitry of a working ECG is very complicated and beyond the capability of an amateur -- a dream for me again. ???
  22. I have found a circuit at the website of Scientific America: http://www.sciam.com/article.cfm?articleID=000C74E4-5172-1C74-9B81809EC588EF21&pageNumber=1&catID=2 The ECG circuit seems to be surprisingly simple. Would it really work -- I wonder. Any one has tried this circuit? Or any others? Oli
  23. Hello every body! I am new to this forum. I wish to build a simple ECG (Electrocardiograph, for one of my family members not having a good heart). This project does not seem to have been a topic of discussion in this forum. Can any one advise me how I should start. If any one can provide me with a circuit, it would be great. Many thanks. Oli
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