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Type: Posts; User: Tunelabguy

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  1. Closed: Re: PCB coating for use in garden soil (moisture sensor)

    This looks ideal. Just what I was looking for. Thanks.
  2. Closed: PCB coating for use in garden soil (moisture sensor)

    I have a PCB design for a capacitive moisture sensor using the PCB traces as the plates of the capacitor. The PCB is shoved into the ground and senses the moisture by the effect on the capacitance...
  3. Closed: Re: magnetic sensor alternative to pressure plate

    I suggest a capacitive detector, like the sensor in a Theremin. It is so sensitive it will detect objects several inches away. But perhaps it will be less sensitive to a floating object without too...
  4. Closed: Re: DC to DC followed by LDO and Inductor in series

    The problem is the ceramic output capacitor. Read the section in the datasheet under Application Information / Output Capacitor. They require between 0.3 Ohms and 22 Ohms effective series...
  5. Closed: Re: DC to DC followed by LDO and Inductor in series

    I would start by looking at the input to the 1117 on a scope to see if the buck regulator is somehow misbehaving. Then check your connections, such as the polarity of the filter caps on the input...
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    Closed: Re: Sensor to ADC interface

    Resolution is a theoretical limitation on accuracy. But as Klaus pointed out, your accuracy is often more limited by other things, such as the accuracy of your reference voltage, or the presence of...
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    Closed: Re: Sensor to ADC interface

    An interface circuit serves two purposes. #1. It can shift the level and range to take full advantage of the ADC range. #2. It can provide a low-impedance drive to the ADC.

    As for #1, the range...
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    Closed: Re: MOSFET which can on fully at 5V

    If you connect 30V across drain and source, you will get either 0 Amps (if the gate is OFF) or 1000 Amps (if the gate is ON), which will instantly destroy any reasonable MOSFET. But this is not a...
  9. Closed: Re: Unwanted piezo-sensitive amplifier circuit

    @Barry: I resoldered a few parts and connected the input to a low-Z source. The noise went away. I guess my mistake was assuming that the 1 Meg load would be sufficient without an input connected....
  10. Closed: Unwanted piezo-sensitive amplifier circuit

    While debugging a little noise problem in an amplifier, I noticed that the circuit is acting like a microphone. Vibrations in the PCB are showing up as noise in the final output.

    The circuit is...
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    Closed: Re: Startup time of 32KHz crystal OSC

    It probably has the same relationship to a second that a mini-computer has to a computer, or a mini-skirt has to a skirt.
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    Closed: Re: Startup time of 32KHz crystal OSC

    It depends on the circuit. But a typical start-up time for such a crystal would be many milliseconds. Maybe 30-60 msec.
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    Closed: Re: Wattage of Resistor in Voltage Divider

    Your wattage figures appear to be right on. However from a practical point of view, your second circuit would have an output of -24v from the op-amp. But the TL072 is only built for a maximum of...
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    [SOLVED]Closed: Re: Select the right Freewheeling diode.

    I agree with FvM that for overcurrent protection, your existing low-side shunt is sufficient, and a lot simpler than high-side current measurement, like I had to do in a similar project, which was a...
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    [SOLVED]Closed: Re: Select the right Freewheeling diode.

    I mean the current sense resistor must be in place of the wire that goes from the anode of the diode to the bottom of the solenoid.
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    [SOLVED]Closed: Re: Select the right Freewheeling diode.

    I agree about the fast Schottkey. You can also say that the diode must be able to handle 6 amps intermittently, and withstand a reverse voltage of at least 24 volts.

    But I want to comment on your...
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    Closed: Re: Why free wire is'nt dangreous?

    That is true. Years ago I saw an article in a radio controlled model airplane magazine that described a wing-leveler auto pilot based on this 100v/m electric field. The model airplane had...
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    Closed: Re: 4n35 line sensing problem

    Here is a simpler solution. Start with the power supply for your microcontroller. Make that power supply from a low-voltage AC transformer. In addition to the usual rectification, filtering, and...
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    Closed: Re: Photodiode noise cancelling, how to?

    You don't understand. Your attempt at canceling the noise may actually make the noise worse, if the ambient light in the side-looking diode is more twice the light the forward-looking one. I...
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    Closed: Re: Photodiode noise cancelling, how to?

    I think your assumption that two diodes mounted in this way will receive an equal amount of ambient light is unjustified. The amount of ambient light received by the two diodes depends on the...
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    Closed: Re: Questions about joule thief

    I had never heard of the "Joule Thief", until I found this Wikipedia article. It is apparently an oscillator that generates pulses higher than the battery voltage.

    From that description I would...
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    [SOLVED]Closed: Re: Gate driver for mosfets

    I was going to say that this is not exactly true. There are logic level MOSFETs that are fully turned on by a 5v microcontroller output. But then I looked again at the OP's micro, and I see that it...
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    Closed: Re: I/Q components and phase

    Measuring the I and Q components of each of the two signals only makes sense if there is some third signal acting as the reference. But determining I and Q with respect to some third signal is no...
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    Closed: Re: Alternative to a bunch of 555 timers

    Yes, it's CMOS. As long as it can sorce or sink sufficient current for the relay coil.

    - - - Updated - - -


    Since the relay coil requires even more current than the 1.35 mA I discussed...
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    Closed: Re: Alternative to a bunch of 555 timers

    Regarding the ULN2803, it has several problems.

    1. It is a Darlington, which means the saturation voltage is two diode drops above ground, or about 1.6 volts in your case. So if your relay was...
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