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    Basic DC Circuits Analysis and Theory

    @jkele: "If two points in a wire are at the same voltage then the difference between them is 0 and this is a short circuit which causes a lot of current to flow however if we have 0V between two points then we have no electric force hence no current flows?" You ask the question as though the...
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    solar lamp circuit without transistors

    From what I can tell, the "tiny paths" are areas where the copper foil has been etched away thereby leaving larger patches of isolated copper foil that connects the components soldered to it. The black blob must be a surface mount device (SMD), possibly a transistor. If you have access to a...
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    solar lamp circuit without transistors

    @marcia "It's on a board where connections are not visible, so how is everything connected?" Even with the poor quality of the photos it seems obvious that the connections are visible. Just assume that anything soldered to a contiguous patch of copper foil is all connected together.
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    Basic voltage Comparator question

    An opamp is a differential amplifier that has been optimized for linear operation with negative feedback, while a comparator is a differential amplifier that has been optimized for non-linear operation and with logic-level output. It is generally possible to use an opamp as a comparator - it...
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    INTERCOM

    In any op amp circuit (that works) you can be sure that the voltage at the (+) input is the same value as the voltage at the (-) input of the op amp. So what is the value of the quiescent collector current flowing through the output speaker? Understanding the quiescent state is your first clue...
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    Help!! - Circuit Design: Voltage divider amplifier

    My datasheet for the 2N3904 has a graph showing Vbe as a function of collector current. Initially you can assume Vbe=0.6 to calculate the collector current, then read the datasheet graph to get a better value for Vbe. Then do another iteration for accuracy. Having a lower cutoff frequency...
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    6v relay problem

    If any of those LED's light up, then you can be sure the relay transistor is toast. If that transistor were good there is no possible way for the LED's to glow because the base of the LED transistor would never exceed 0.6 volts.
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    6v relay problem

    Let's assume you are using a Panasonic HC relay. Go to the Panasonic relay page at http://pewa.panasonic.com/components/relays/power-relays/general-purpose-power-relays/ and download the HC catalog: http://pewa.panasonic.com/assets/pcsd/catalog/hc-catalog.pdf Find the HC relay data for the 6...
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    relay control circuit

    The R2C1 time constant is 1 second so it takes C1 about 5 seconds to become fully charged. Just change R2 to something around 100K so it will charge up in 0.5 seconds. That is the first thing I would try. Changing C1 to a smaller value could make the reset unreliable.
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    relay control circuit

    You may not have to do anything at all, as long as R3 & R6 are rated at least 1/4 watt. Measure the relay coil current when driven with 28 volts. DC current gain of Q3 is specified at least 100 in the 10 - 150 mA range so Q3 should remain saturated up to (28 - 0.6)/(4.7K + 10K)*100 = 180 mA of...
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    Circuit design help

    Have you thought about doing a prototype with an audio stereo amplifier? You could use each channel to drive a full-wave rectifier to provide a varying DC voltage to the motor. The DC voltage would be proportional to the sound volume, and the volume control would give a simple method to adjust...
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    Water heater project

    Don't know about your setup, but at my place the water heater and pool equipment are both on 240 VAC circuits. Plus the water heater can draw up to 6 kilowatts so you will need to find a hefty relay. Just make sure you know what you have and what you need.
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    Flashing LEDs

    What you describe I believe can be implemented rather simply as a state machine with JK flip-flops (e.g. CD4027). The mode line controls whether just the green LED flashes or all LED's fire in sequence. Note that the K input on all flip-flops is at a logical "1" so the J input controls whether...
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    LED Panel Circuit

    While my comment about Edison using a rheostat may have seemed sarcastic, I was not suggesting that a rheostat would be a poor solution. In fact, it might be the best solution for your purposes (unless some of your purpose is to learn about modern electronics). A rheostat would offer an...
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    LED Panel Circuit

    Using a high-current rheostat as a dimmer is probably how Thomas Edison would have done it back in 1880. So you would be in good company.
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    Protecting a circuit - ideas

    The old standby coil coating is GC Electronics Polystyrene Q Dope. http://www.gcelectronics.com/order/SubCatPDF/thinners%20Solvents%20Coatings%2055-56.pdf
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    RF Signal Strength meter (was Wiring a potentiometer correctly)

    Can anyone explain how that diode rectifier section is able to work? I have read the original explanation available at http://www.talkingelectronics.com/projects/FieldStrengthMeterMkl/FieldStrengthl.html but just can't seem to visualize what is going on in there.
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    Interfacing with a switch in an external circuit

    According to the PIC datasheet the RA1 pin is a tri-state I/O port which in the floating state acts as a high impedance input port with leakage current of +/- 1 uA and TTL logic levels, i.e., 0.0-0.8 V is logic Lo, 2.4-5.0 V is logic Hi. The first question is how large can R1 be and still pull...
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    Solutions please for the novice.

    So you need a high-current switch controlled by a lower current. That would either be a transistor or a relay. Since you already have the delay switch w/LED (20 mA?), and the glow plug draws 100 times that current (2 A?), then just find a high-current transistor with a DC gain of 100. Drive...
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    Opamp circuit help needed

    It was not really obvious to me how the circuit worked so I tried to analyze it. For analysis purposes the circuit can be simplified. R1 can be replaced by a Thevenin equivalent bias voltage Vb and source resistance. The equivalent input resistance Ri is determined by the setting of R1, R2...
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