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  1. R

    RF basics

    Thanks for the help.
  2. R

    RF basics

    Thanks for the help. I have a couple of more questions please: 1. Why are standing waves undesirable? 2. How do you design a PCB antenna for 50R? Thanks in advance.
  3. R

    Wanted: Student Manual Art of Electronics

    Thanks for the link.
  4. R

    Active high signal

    Yes, they share the same 3V3 line and OV.
  5. R

    Active high signal

    Hi all, I have an active high signal on an IC. This puts the IC into shut down mode. It is connected to an I/O line of a PIC. Can i connect the shut down pin to OV via a 10K pull down resistor, this makes the IC active. Then output a logic 1 from the PIC to enable shut down i.e. making it high...
  6. R

    RF basics

    Hi, I am new to rf design. I have been given a project that uses a 868MHz rf chip. Are there any good sites for beginners with minimum maths? Also what is carrier frequency, frequency deviation, preamble. Lastly, how does crystal selection select the frequency i.e..868MHz? Thanks in advance
  7. R

    Protection of Lithium Batteries

    Thanks for your help.
  8. R

    Protection of Lithium Batteries

    I am looking at energizer AA lithium batteries. These have 3000mAh. Each cell is 1.5V. I have a further question. If i have 4 of these. I need to get 3V. So this is easy i.e. put 2 in series. Can i put 2 more in series and then connect all 4 in parallel to give me 3V at 6000mAh? What...
  9. R

    Protection of Lithium Batteries

    Thanks.
  10. R

    Protection of Lithium Batteries

    Thanks for your reply. Please can you let me know what you mean by ORing diodes? Is it a wired OR? I dont understand. Thanks
  11. R

    Protection of Lithium Batteries

    Hi all, I am looking to parallel a few Lithium Coin Cell Batteries i.e. CR20332. Could I put in Schottky diodes in replace of the PMOS FETS in the image attached? Or will I not need to use anything as the batteries are not Lithium Polymer type? Best regards, Raj
  12. R

    Interfacing arduino mega 2560 to 3v circuitry

    Hi all, I am using an Arduino Mega 2560. This is to be connected to some circuitry which runs off 3V. I have seen the following TXB0108 level translator. However it seems to me that it is a 3V to 5V translator. Where i need 5V to 3V. Can anyone help?
  13. R

    Pic interface with sensor

    This is the info for the gas sensor. Any help would be aporeciated. Thanks.
  14. R

    Pic interface with sensor

    Hi I have tried to post a scematic in different formats all less than 3mb but get errors. Output needs to be 0.65V (tolerance of 1%). The width has to be 100ms. I have generated the pulse using a dc dc converter Ltc 3549, which gives exactly the output i require. The sensor heater is at 150mA...
  15. R

    Pic interface with sensor

    Hi How can i switch a 0.65V pulse? I am testing some sensors and 0.65V pulse is required for the heater voltage. I was thinking of using a pfet high sude switch. Drain as output, source at 0.65V pulse. Gate to drain with a pull up to keep the fet off. The other end of the pull up connected to...
  16. R

    Pic interface with sensor

    Hi all, I have managed to find a dc-dc converter that with feedback resistors, i can achieve 0.65V DC pulse. It is the LTC3549. The design has changed, where i need to test 5 to 10 sensors for comparison. I thought i could use a high p fet switch and drive it with a pnp transistor. I am not...
  17. R

    Pic interface with sensor

    The gate is driven by the micro, drain is at 0.65V and source is at 0V for a n channel mosfet? Is that wrong?
  18. R

    Pic interface with sensor

    Ok. I will try and use a psu set to 0.65V. I have no idea if i should use a p or n mosfet for the switching. Could you assist. I think n mosfet would be easier to drive and it might have lower rds on. Can you advise?
  19. R

    Pic interface with sensor

    Sorry, i will keep it everything in this thread. My issue now is the drive to the heater. Looking at the datasheet the heater has a resistance of 1.8ohm (when cool) and i presume this will increase slightly when the 0.65V DC pulse is applied. I need a circuit to drive this low kmpedance 1.8ohm...
  20. R

    Pic interface with sensor

    I need to find a way of generating 0.65V DC. Cheap with minimum components. So thought i could charge a cap to 0.65V (diode drop) then discharge. Hopefully giving me a pulse output.
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