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    Anyone used an LM2931-5.0?

    Steve, The LM2931 regulators draw a lot of current during the rise of the input voltage, until the output reaches regulation. This is because the internal control circuit rather stupidly applies full base current to the PNP pass transistor, in an attempt to increase the output voltage...
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    Help in Timer circuit

    Katherine1, An LCD would be an option, but will add some complexity to both the hardware and software. Also adds to the expense. No need for it, according to your original "specification". A display could show time remaining, but you need to be careful about "feature creep". Even...
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    Help in Timer circuit

    Katherine1, The microcontroller approach can result in a very simple hardware design. This is how you would want to design the device for mass production. However, depending on your current programming skills, it might make the project much bigger for you, possibly taking too long to...
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    How to trigger a triac?

    Triggering triacs can be very complicated. Both the gate current and the load current through the main terminals are important factors, along with time and temperature. Polarities matter. 2us seems like a pretty short time. Triacs tend to be slow. To get more specific advice you will...
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    Help in Timer circuit

    Katherine1, I think most of the digital circuits shown in the linked pages switch the buzzer circuit to different digital counter outputs to set different delay times. This leads to times that progress by powers of 2: 1, 2, 4, 8, 16. It would also be possible to switch different...
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    Help in Timer circuit

    Katherine1, It sounds as if the timer needs to work pretty well, and that this may be more important than I imagined it was. There is no doubt that the digital timer circuits will provide more reliable performance, for the longer times that you need. The ”CMOS Pocketable Timekeeper"...
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    What did I do wrong?

    Steve, I thought I was answering the OP's last LED question, which appeared to me to concern the LED in the original circuit he linked early-on. However, I must admit that there is an LED in the low battery detector circuit as well. I have to say that this low battery detector...
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    Help in Timer circuit

    Katherine1, I think you can make your original plan work well enough. All of the problems mentioned are valid, but your requirement is not for precise timing, I think. I suppose that you intend to make one or two units for experimentation and personal use. The answer would be different...
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    What did I do wrong?

    The LED indicates that the charger is in the constant current mode. This is the first part of the battery charging sequence, when the battery is being charged rapidly, and its voltage is relatively low. The battery voltage gradually rises during this part of the charging sequence. Once...
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    What did I do wrong?

    As already mentioned, an LED without a current limiting resistor is not a suitable load for the charger circuit. You really need a lower resistance trimpot, but the 100k one might work. You might disconnect the trimpot from the circuit, and see if you can set it to values around 2k to 3k...
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    3V to high voltage inverter

    sauroman1, Disposable camera inverters usually provide a 200 to 300V DC maximum output. The frequency is often a few tens of kHz at full voltage. The frequency is lower as the flash capacitor begins to charge. You may be able to hear it. These circuits are designed to work well over a...
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    3V to high voltage inverter

    sauroman1, Sounds as if you are making progress. Note that the AC frequency may be too high for your multimeter to measure properly. Often the AC ranges on these are only good for power line, and possibly low audio frequencies. It is possible that touching the connections overloads...
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    3V to high voltage inverter

    sauroman1, Thanks for the pictures! It is still not clear what sort of "C547B" you have. I don't recognize the manufacturer's logo. If that is the only one you have and it is now dead, perhaps it does not matter. Don't power-up your circuit again with any transistor, until the...
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    3V to high voltage inverter

    sauroman1, I had a chance to look into your transistor. Is C547B the complete part number? Who is the manufacturer? Can you post a link to a data sheet? I think this number might signify a GE SCR. That won't work in your inverter circuit! Often the marking on the part is not...
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    3V to high voltage inverter

    sauroman1, You should know that the schematic, both as seen in your original post, and on the linked page, has a typo that will prevent the circuit from working. The transistor's base and collector connections are reversed. This will tend to destroy the transistor when power is...
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    DB25 Parallel Port Programming

    Hiigarangh7, You are very welcome. The forum members are eager to help you. We could be of more help if you shared with us more details about what you are working with. We can make all sorts of guesses, but the resulting answers may not be useful to you. So far, you have mentioned a...
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    Component help

    Screwball, Perhaps you could tell us a bit more about what you are trying to accomplish. I realize that you initially asked about transistor selection, but that was not the entire question you need to have answered. Some things we would like to know include: What is your power source...
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    DB25 Parallel Port Programming

    Hiigarangh7, Since this is getting a bit overdue for some sort of answer, I'll give it a try. Perhaps there are no answers because we really need to know more about what you are working-with. Also, the cable you mention buying does not seem to be what you will need. What sort of...
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    Hall Sensor - Limit Voltage

    David, To best answer your question we need to know more. Is it possible to tell us the make and model of your sensor, and something about the device or circuit it is to be driving? Can you provide links to device data sheets, and circuit schematics? A general description of what you...
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    L7805CV 5V Voltage Regulator 1.5A

    StealthRT, If you are wiring-up that thing with clipleads, it still may not work, even if the connections are not scrambled. Many of these parts will oscillate at some RF frequency unless the input has a capacitor connected right across the IN and GND terminals. If the capacitor is at...
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