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    Understanding The Following Circuit

    Hi All, I was wondering if someone can help me understand the attached circuit. this is what i have measured:- Input to the opamp is -0.5V (from a PSU), because of feedback the inverting terminal must be at the same potential ie -0.5V because of virtual earth of opamp. The gate of the FET is...
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    LED monitor using phototransistor

    Hi all, I have a requirement to monitor a LED using a photo transistor. The LED is powered from a 3V3 supply via a resistor, the cathode if the LED is going to a I/O line of a micro. So a logic 1 keeps the LED off and a logic 0 lights the LED. If I use a phototransistor, do I need to match the...
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    op amp question

    Hi all, I have a op amp circuit powered from +5V and -5V supply rails. If the non inverting input is sitting at 1V. If I now put a -2V on the inverting input. Should the output still go negative. Sorry this has been puzzling me. Best regards, Raj
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    detecting low voltage with PIC

    Hi, I have a Pic micro that drives a LED. The circuit is 3V3 through a 270R resistor, to the anode if the LED and the cathode is connected to a I/O line of the PIC. So a logic 0 lights the LED, a logic 1 keeps it off. Can I connect this cathode / PIC IO line to another PIC microcontroller input...
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    pull down resistor for npn relay driver

    Hi all, I have the attached circuit diagram. I wanted to know if there is any way of calculating the value of the pull down resistor. I don't want the relay to be driven on when the microcontroller is switched on. My understanding was that if the output from the PIC is OV. Then the transistor is...
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    Clarification on LED millicandela and light output

    Hi all, I have two LEDs which have the following specifications LED1 LED2 VF 3.0V 3.2V IF...
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    LED replacement

    Hi, I am looking for a secondary source for LEDs in a project. I am looking at the following specifications to make a comparison, have missed anything out? Dimensions Pitch Colour VF forward voltage If forward current Reverse current Min and Max current Lumens output in MC milli candela...
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    Low value resistors

    Hi, I have a application in which i am switching low value resistors i. e. 0.1R, 0.2R, 0.4R etc to a unit under test. I have come across a problem, track resistance and cable resistance which override the resistor values. These are software selectable so need relays to switch them to the end...
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    LED monitoring

    Hi all, I have a project in which I need to monitor a couple of LEDs for activity. This is part of an automated system. The LEDs are driven from a microcontroller. 3.3V, then a resistor with the LED cathode connected to the micro I/O pin. So a low signal will trigger the LED on. Could I...
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    Detecting positive and negative edges

    Hi all, I need some advice. I have different sound patterns that are driven from a microcontroller. They vary in pulse width and duration according to the different alarm patterns. They are used to drive a piezo circuit. I need to monitor the sound patterns to determine which alarm occurred...
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    Understanding if this circuit

    Hi All, I was wondering if somebodycan give me some help in understanding this circuit. The first stage is a inverting amplifier stagevwith gain of -1. If I put in 0.5V I then get -0.5V. This goes into a second stage which the N channel FET is in the feedback loop of the opamp, It is a negative...
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    Led flashing for one second using Mikro c

    Hi All, I am currently writing some code in C on Mikro C platform. The program is supposed to doba led chaser on port D of pic18f54k20, I am using debug PCB on pickit 3. Then it's supposed to flash led on port c bit 0 every second. It does the led chaser routine but never goes into the...
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    Capacitor / filtering for PSU

    Hi, I am designing a 19' inch rack system. A Switch mode PSU offering 5V, +/-12V has been selected. I am using the 5V supply to generate a 3.3V supply for a micro and DAC. The 5V will also supply the +ve supply for a 0P1177 opamp. What filtering would I need for the 5V output from the PSU. Would...
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    Python and Mikro C

    Dear all, I am currently learning Python. I wanted to start a project that allows me to build a GUI in Python which allows me to set LEDs on a PIC microcontroller (PIC18F4520). I am using Mikro C. I am thinking of using FDTI from PC USB to RX/TX (UART) of the micro. The GUI will be very simple (...
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    Voltage regulator 7905 capacitors.

    Hi, I am using 7905 regulator and would like to ask the capacitors that are required. The data sheet says 0.33uF across input and 100nF across the output. I have seen 10uF across input and output too. My question is should the 10uF be electrolytic, tantalum or ceramic. Low ESR type? I would...
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    PIC A/D question

    Hi, I am looking to use a PIC A/D channel, the PIC is PICLF1936. I have used a forward biased diode connected with a 1K resistor to measure temperature, every 2mV gives a degree change. I am trying to implement the same with a voltage divider. The network set to 500mV, using a 10k (source...
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    Filtering for USB5V

    Dear all, I am doing a project that powers off a USB port I.e. 5V. This will be used to get a clean 5V line, generate a 3.3V from LDO and also a -5V supply using a charge pump IC. I know that USB5V is noisy. Could someone give me ideas on filtering this. I have seen pi filter arrangements but...
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    Programmable negative constant current source

    Hi, I was wondering if someone could help. I am building a programmable negative constant current source. The idea is as follows: DAC controlled from a microcontroller fed into the non inverting input of an opamp. The opamp has split supplies +/-5V. The out put of the opamp drives the gare of a...
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