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  1. R

    LED forward voltage and brightness

    Hi Bob Thanks for your reply. So am.i correct in saying that if i increase the current the LED will be brighter and get closer to the mcd value of 200? Thanks in advance.
  2. R

    LED forward voltage and brightness

    Hi I wanted to ask a question on LEDs. If i have a 3V3 supply and using a LED of 2.1V forward voltage and IF of 20mA.the mcd is 200. I tend not to run st full 20mA but give some head room so 15mA is what i normally use. To calculate the required resistor is R = 3V3-2.1V/15mA How is this...
  3. R

    Capacitance on PIC I/O line

    Thanks for your advice guys, much appreciated. Is excess current draw through the capacitor when the voltage changes suddenly also a problem associated with capacitors.
  4. R

    Capacitance on PIC I/O line

    Hi I wanted to ask a question regarding capacitance on the input of a PIC I/O line. Why is this undesirable? Is it because if we get a voltage rising quickly then we will get a sharp rise in current due to the capacitance? Hence we must keep try and keep the capacitance as a low value? Also...
  5. R

    Calculating current limit resistor value

    Hi Bob Connecting the unit to a PC via FTDI lead, so we can download information from the units EEPROM. Thanks.
  6. R

    Analogue Electronics Practical Experiments

    Hi thanks for the recommendation. I will take a look.
  7. R

    Calculating current limit resistor value

    Hi Bob Thanks. Is there away to calculate this properly? I thought it would be R= 0.8VDD/ 2mA = 1.2K. Is that wrong? Also do i need an internal weak pull up on the PIC? I do not know what the point is by having it. Thanks in advance.
  8. R

    Calculating current limit resistor value

    I cant seem to upload the file but this is what i have: PIC ---TX-----------------------33R resistor----------- | | ------- ------- 39pF | | ----- 0V
  9. R

    Calculating current limit resistor value

    Hi Here is a schematic showing only the TX line. The RX line is the same. They both go to the connector on the right hand side which is used to read data from a unit. Do i need an internal pull up? The PIC can source or sink 25mA, i want to adjust the value of R1 to limit well below this...
  10. R

    Analogue Electronics Practical Experiments

    Hi i am after understanding and building circuits using transistors, capacitors, FETs, Opamps, diodes etc. I can understand some stuff but cant get the concept of using individual components to build a circuit.
  11. R

    Analogue Electronics Practical Experiments

    Hi all, I am trying to get better at analogue electronics. My main issue is that i cannot read what is going on in a circuit. I am currently reading a Basic Electronics book to understand some theory work. I also need to be building some circuits practically. Can anyone recommend a good simple...
  12. R

    Calculating current limit resistor value

    Ok. I will draw out the schematic for you today. Thanks for your help.
  13. R

    Calculating current limit resistor value

    Hi Please could you elaborate with the example above? Do you mean it will be different when the I/O lineis either teceivjng or transmittibg.
  14. R

    Calculating current limit resistor value

    Hi I have a 33R resistor and a 39pF cap to 0V. Note: First it is the 39pF connected the PIC I/O then to 0V. The 33R is then from the capacitor to a 3 pin header. The 33R is connected to the TX line of a PIC. I think the PIC can sink or source upto 25mA. If the output of the TX line was VIH ie...
  15. R

    2 layer and 4 layer pcb

    Hi all I am starting to get familar with schematic capture using Eagle PCB. I am now ready to do some simple pcb designs. I am looking st a 7 segment pcb as a starting project. This fits into a microchip development board that i have. So it will be a small module pcb. The bosrd will plig into...
  16. R

    Understanding N channel and P Channel FETs

    Thanks will get a copy.
  17. R

    Understanding N channel and P Channel FETs

    Hi all I have always had difficulty in understanding how FETs work. N channel and P channel also all the variants such as enhancement and depletion types. Also the operation modes ie. Linear mode triode mode etc I would like to learn this practically. Are there any good resources where i could...
  18. R

    PIC A/D sampling help

    Hi Thanks for the replies. This is the output that i get from the hardware. It is 4KHz, signal. So i should sample at least at 8KHz. I can't change the hardware, as PCBs are already done. Hence this is why i asked about using software. All i want is to distinguish between the two waveforms...
  19. R

    PIC A/D sampling help

    Hi I have attached two waveforms that are going into a PIC18F4520 micro A/D pin. The PIC is powered from 3V using the VDD (3V) as the internal reference voltage. Waveform 2 should be easy to measure, it settles at 900mV. I am struggling with waveform 1, which cycles through 1.3V and 800mV...
  20. R

    Capacitive reactance affecting voltage divider output

    Hi Thanks for the message. The unit is enclosed, so he cant look at it. He must periodically test it (once a week) to ensure it is connected.
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