Search results

Search Forums New Posts
  1. R

    Help With Circuit

    Hi, Thanks for your reply. The schematic is incorrect. I have a n channel with drain to 0v, in between drain and 0v is the sense resistor. Then this is connected to the opamp. If the drain is at 0v then I need the source to be at a lower potential I.e. -5v. Is this not correct? Thanks in advance
  2. R

    Help With Circuit

    Hi Steve, Thanks for the help. I did point this out in my previous post when you drew the circuit i.e. that the get you have is a p channel. I have replaced this with a n channel. Drain to 0V with sense resistor and source going to load with the other end of load to -ve. Is that correct I.e. n...
  3. R

    Help With Circuit

    Hi Steve, Thanks, if i use a n channel fet, then i can have the drain to 0V with resistor to non-inverting input and then source to output with the other end to -v supply. Do you remember that you helped me once before? I am still trying to understand the circuit you helped me with. i have...
  4. R

    Help With Circuit

    Hi all, i have attached the following circuit. it is basically a opamp driving a n channel fet used as a constant current source. the drain of the fet is connected to 0V, the source is at -5v. the gate is driven from the opamp output via 100R. my understanding that the opamp will drive the fet...
  5. R

    6 layer pcb stack

    Hi all, I have a coupe of questions: i have a 6 layer pcb, the stack up is as follows layer 1 - component (smd and through-hole) + tracking of analogue signals layer 2 - gnd layer 3 - inner track for digital signals i.e. spi, i2c layer 4- inner track for digital signals i.e. spi, i2c layer 5...
  6. R

    PIC Micro Output I/O

    If we have a push pull I/o line
  7. R

    PIC Micro Output I/O

    Hi, I have a question regarding the PIC18F4520 micro. If i connect a 10K pull up to one of the pins and make this as an output. I believe that this will be a logic '1'. If i now make this (still as an output) but output a 0, how can the output be a 0 since it is connected to VCC via a 10K...
  8. R

    MOSFET to replace a relay

    Hi, I need to replace a relay with a MOSFET. The relays have very low contact rating is 30milli ohm. I need to switch low value resistors typically 0.2R. I am measuring currents in the 2uA range, so can't afford that to be affected. The relays are controlled from a PIC micro. Is there any...
  9. R

    A few questions on electronics

    The master clear is a active low signal. So I thought to disable it would need to be a high, then reset via a FET connected to the pullup, to drive the pin low when we wanted to reset.
  10. R

    A few questions on electronics

    The shift register is connected to a ULN2003LV to drive 5V relay coils. So I didn't want them to chatter on power up.
  11. R

    A few questions on electronics

    Hi Bob, Thanks for your help. I wasn't sure the state of the micro I/O lines on power up. So hence the pull up, to make the master clear high, disabling it. I wanted the FET to give me control of this line, so that I can pulse this low to reset the shift register anytime I want. My requirements...
  12. R

    A few questions on electronics

    So for the FET, am I safe today I can connect gate to 0V via a 10K pull down resistor. Then a 470R from the gate going to the micro I/O. But how do you calculate these values from FET characteristics and micro I/O output drives?
  13. R

    A few questions on electronics

    Thanks for your answers.
  14. R

    A few questions on electronics

    Hi all, I have a few questions that I wonder if you could help me with. 1. If a electric MIC has an output impedance of 2.2K, does that mean anything I connect to it must have an input impedance greater than 2.2k? 2. I need the MIC output to be coupled then to an opamp, the value of the...
  15. R

    Piezo To Detect Sound

    ok thanks for your assistance. so an electret mic, amplifier and comparator or similar woul ddo the trick?
  16. R

    Piezo To Detect Sound

    Hi, I am considering a project where i can use a piezo buzzer to detect sound rather than using a mic. I have seen different types of piezo buzzers, some with 2 wires and some with 3 wire. I think that the 3 wire has an additional feedback signal. Not sure. Is this a possibility? I am trying to...
  17. R

    sound patterns

    hi thanks for your prompt reply. Please could you explain why the 10nF will not damage the inverter. i belive that in this state it will be used as a current sink output pin, is that correct? is it due to current flowing through the 10nF will be less than say a 100uF? not sure? i did try the...
  18. R

    sound patterns

    Hi, many thanks for your help. I have one question, when the diode is forward biased, it stops the capacitor discharging. Is the discharge path through the cap to the diode and the output pin of the Schmitt trigger. Is that correct, are there any potential issues with this? Best regards, Raj
  19. R

    sound patterns

    Hi, Thanks for the description of the circuit, it makes sense. A quick question, do I need both circuits or just one. Do I need the monostable and retriggerable circuit or only one of them? Thanks Raj
  20. R

    sound patterns

    Hi, I need it to accurate, at least to distinguish alarm patterns as mentioned previously. I like the idea of the retriggable monostable. But if I use this what happens when there is no pulse I.e. space Skills are a mixture although not do good with hardware side of things. Last sequence is...
Top