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    Measuring CR123A battery using PIC A/D

    Hi all I have a CR123A 3 V battery. I am trying to monitor the condition of this using a PIC 18F45k20 A/D. This is my approach. 1. Use the Vdd and Vss of the battery as my PIC reference. This will be used to measure off load battery levels. 2. I then intend to use a voltage divider 30K top...
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    Pcb as antenna track

    Hi all I am looking at doing a project with 433MHz radio modules. I think that 3x10 (power8)/433MHz is 0ne wavelength. If i divide this again by a quarter to get a 1/4 wavelength. Just say this came to 7cm as an example. I want to know how i can make a PCB track to act as an antenna. Say it...
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    N channel Fet v npn

    Hi all I was after some help regarding n channel fets v bipolar npn. I want to conduct a simple experiment so I can understand the differences when using these transistors as switches. I want to switch an led powered from 9V using both transistors. So basically 2 different circuits. One with an...
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    Pressure sensor for focus pads

    Hi all, I am starting a project that will display the force that someone has hit a focus pad. This will be used for boxing practice. The idea being yiu hit a focus pad and then a displsy registers how hard you have hit the pad. I am a little stuck on the method to detect the strike. I was...
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    switching the VSS line of an IC

    Dear all, I have a IC which I need to switch off when not in use as it draws a current of 100uA in standby. I think the best way of doing this would be to disconnect the 0V line via a switch i.e. transistor or FET. I have one pin of my PIC I/O line which I could do this with. I am looking at a...
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    EMC good practices

    Hi I was wondering if someone could help me with the following EMC and PCB layout questions: 1. Why is it good to have a separate layer dedicated to the GND? Is it because it is a low inductance/resistance path to ground? i.e. less voltage spikes? 2. Are track lines meant to be short as...
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    Detecting an active low signal

    Hi all I need some help with a problem. I have 2 x PIC microcontrollers on seperate PCBs that communicate via SPI. They connect via a 8 pin header. One is a master the other the slave. I need to detect when tbe slave PIC has bern disconnected from the header. I have MOSi, MISO,CLK and Slave...
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    Peak detector to A/D of PIC

    Hi all I have a peak detector circuit below. However when i connect this to the A/D pin of the PIC i get a flat line ie 0V Could this be an impedance matching issue? I have aldo noticed the same thing happen if i attach a low pass RC filter to the PIC A/D ie 100K and 220nF I have thought about...
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    Volts per metre

    Hi all, I have a question regarding volts per metre or v/m. I know that this is a unit to measure electric field strength/intensity. I believe thst when we say 1V/m it means at a distance of 1 metre a voltage of 1V strength is applied. I also know it is used in EMC immunity tests. My question...
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    Good PCB layout design practices

    Hi all I am learning some schematic capture and layout with Eagle PCB. I eanted to ask whst is generally good PCB design practice. Is it some of the following: 1. Segregate Analogue and Digital circuitry 2. Decoupling caps on all ICs 3. 4 layer stack up woukd be signal gnd power signal 4. Have a...
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    Square wave to DC level

    Hi all I have a 0 to 7V square wave signal. Frequency is 4KHz. I want to convert this into an 0 to 3V signal to be read into PIC A/D or Comparator. My initial solution was to use a voltage divider to reduce to 3V, This still leaves me with a 3V square wave. Can i use a low pass filter then to a...
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    Opamp to pic a/d

    Hi I just wanted some advice. I have a signal of 25mV. This i want to feed to a PIC A/D pin. However i eant to amplify this to say 2.5V. Would it be ok for me to use a non inverting opamp and suitable resistors to provide the gain/amplification? Do i need any care in selecting the resistor...
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    Clamping circuit for PIC A/D

    Hi, I was wondering if someone could help me. I have a 60V pk to pk signal, which has a current of 200uA, so not much. I need to clamp this so I can feed this to an A/D input of the PIC microcontroller (PIC18F). The PIC can have its A/D from 0-5V My solution is to use a resistor and zener diode...
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    Electronics help

    Hi, Please could someone explain the difference between solder paste, solder mask, solder resist and paste mask. It confuses me. My second question is what is the connection of pcb track length with wavelength? How can a track become an antenna at certain frequencies. I look forward to any help.
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    A/D source impedance

    Hi all, I am looking to do some A/D measurements with a PIC microcontroller. The PIC datasheet states that it has a source impedance of 10K. Does this mean, I need to drive it with something that is lower in value so that it won't load the signal. I have a voltage divider connected to this pin...
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    understanding discrete circuits

    Hi all, I have a Btec OND in electronic engineering. Which I qualified for a few years ago. My question is that I find it difficult to analyze circuits that I have seen to figure out what is going on. Something with say 3-4 transistors NPN and PNP starts to baffle me. I look at a circuit and...
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    Wanted: Oscilloscope help

    Hi, I am looking to purchase a oscilloscope, my budget is not great. But I will be using it for the following experiments. 1. Monitoring SPI, RS232,I2C signals using PIC microcontroller 2. Analogue elevtronics, filter design and simple circuits like waveform generation 3. Basic digital...
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    Understanding impedance

    Hi, I am a relative novice in Electronics. I can never truly understand the meaning of impedance. I understand it is a measure of resistance at AC (which includes inductance and capacitor reactance. What I can't understand is when I here for example 'This circuit has an input impedance of 10K'...
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    Wanted: Transistor Circuit Techniques Book

    Hi all, I am writing to see if anyone has the following book Transistor Circuit techniques by Gmail Ritchie. It's £48 on Amazon, I was wondering if anyone has this book for sale at a cheaper price :) Thanks in advance
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    Resistor across LED

    Hi all, I have a question. There is a circuit of an LED and 680R resistor. The LED is powered from 3V, the 680R is driven from the I/O line of a PIC, so a logic 0 will light the LED. However, across the LED anode and cathode is a 10K resistor. What is the use or idea for this? Can anyone help...
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