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  1. R

    Programmable negative constant current source

    Hi Steve, I tried to follow the equations but do not understand them. I get the inverting amplifier but nothing else. Sorry but could you explain it? I don't understand the current calculation, or if you could give me a hint. Best regards, Rajinder
  2. R

    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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    PIC A/D question

    Sorry should be PIC16LF1936, my mistake.
  4. R

    Python and Mikro C

    Thanks for the advice. I want to break this project up into smaller manageable projects. I want to check that my serial comms works. Would it be a good idea to write a Python program to send characters and use a terminal program to see if they are sent successfully? Something like RealTerm etc...
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    PIC A/D question

    Let me upload again, sorry. Here it is. Best regards, Rajinder
  6. R

    PIC A/D question

    Hi Adam, Sorry for the delay in getting back. I have attached a circuit diagram. The Output voltage from the DAC will be adjusted 0-3.0V. The voltage from the potential divider fed into the A/D channel of the PIC. The voltage divider gives 500mV. I need this to be between 500mV to 640mV. I know...
  7. R

    Programmable negative constant current source

    Thanks Steve No it wasn't homework. I needed to connect the circuit to another circuit but have a common ground. That's where your advice and suggestions helped. Best regards, Rajinder
  8. R

    Python and Mikro C

    Hi Harald, Thanks for your help. You make it sound easy. I have never done any work with serial comms and this may be tricky without further reading. I should be able to generate a GUI and get the PIC to read the ASCII text. My PC gas no serial port (9 way). Hence I am having to use USB to...
  9. R

    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 (...
  10. R

    Programmable negative constant current source

    Hi Steve, I apologise for the questions. You helped me with the negative programmable current source. Would you be able to answer a few questions please. 1. My thoughts were to use a n channel device with drain to 0V and source provide the negative voltage. As the drain is more positive than the...
  11. R

    Programmable negative constant current source

    Hi
  12. R

    Voltage regulator 7905 capacitors.

    Hi Adam, Thanks for your reply. I always have been told that 10uF + 100nF at the input, the 10uF should be low ESR. The same at the output. Alot of engineers have told me to use tantalum and not aluminium capacitors for the 10uF. I am not sure 100%, so need to really understand why we select...
  13. R

    PIC A/D question

    Hi Adam, Will upload one asap. Thanks for your reply. Best regards, Rajinder
  14. R

    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...
  15. R

    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...
  16. R

    Programmable negative constant current source

    I have wired the circuit with a n channel, drain to 0V, sense resistor taken from source and voltage feedback from this to inverting input of opamp. You have a P channel FET. I am not sure why my circuit is working correctly? Any ideas? Best regards, Rajinder.
  17. R

    Programmable negative constant current source

    Hi Steve, Thanks for all your help with this problem I wanted to ask something. My understanding of the n channelosfet for this design is that Drain voltage must be greater than source voltage. Also gate voltage must be greater than vgs threshold. So am I correct in saying that because the...
  18. R

    Filtering for USB5V

    Hi thanks for your message. I am using the USB5V to obtain a 3V3 supply, 5V and -5V supply. Also to supply voltage to power up a external reference for a DAC. The 3V3 will power the DAC and microcontroller. I have not yet monitored the USB5V supply line for noise but will do. But I have some...
  19. R

    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...
  20. R

    Programmable negative constant current source

    H Hi Steve, Many thanks for your help. The circuit works as expected. Thank you again for your help. Best regards, Rajinder
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