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Recent content by vitoa

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    125MHz peak detector Help optimize circuit

    Hi, I need a peak detector working at 125MHz to measure a variable capacitance between 4pF to 30pF The oscillator outputs 0V to 3,3V square wave at 125MHz and I need to get a proportional DC voltage output to capacitance value (4pF to 30pF). First all, will diode 1N4148 work well at 125MHz? or...
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    AC Wheatsone bridge equivalent impedance at AC

    Thanks for simulation. Bridge setup is not the best for this application ,so this circuit will fit better the propouses.
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    AC Wheatsone bridge equivalent impedance at AC

    Hi, thank you very much for this simulation. It seems my circuit is not working as I expected. I only have square wave oscillator for this setup. But I found alternative methood to do good measure of capacitive probe with good results. Any one could help with the simulation of this circuit...
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    AC Wheatsone bridge equivalent impedance at AC

    Some one to help me solve this wheatstone bridge and calculate R's Any quick simple simulation if possible Thanks
  5. V

    Use RF 100MHz to measure soil moisture IC generator plus IC detector

    Hi, for new design I recommend this setup. This will adjust better range because AD8307 is logarithmic. So find better range for probe on wet and probe dry. Adjust R until get most difference between wet to dry probe voltage output. If you do not want 100MHz or 80MHz you can use any...
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    Use RF 100MHz to measure soil moisture IC generator plus IC detector

    Water salinity influence measures at low frequencuies. See this paper. Most linear to measure and transparent to minerals is 380-485MHz range
  7. V

    Use RF 100MHz to measure soil moisture IC generator plus IC detector

    Yes absorption/reflection. For light there is an examle ir ligh sensors with emitteur and receiver ir led's. Paralell pcb plates act as small antena cylindrical pattern. It starts detecting hand reflection at 15cm. Maybe a 15cm antenna range.. Inside soil it measures moisture. Soil wet...
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    Ampop subtractor operational OPAMP amplifier subtractor circuit help

    Hi the ideia is this one, need to get porportinal output from AD8307. AD8307 will output 2,7V to 3V range. Need to use 2.5V referece IC Voltage divisor is to get output 3V down to 2.5V. Compare variable voltage to 2.5V .Variable voltage drop 0.5V with resitor divisor. AD8226 is good choise...
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    Use RF 100MHz to measure soil moisture IC generator plus IC detector

    FDR soil sensor working. Probe range is 15cm to detect hand, few mV change. wet soil to dry voltage difference 300mV Measuring soil volumetric water content 15cm radius. Using 80MHz Salinity insensible. Need to amplify this voltage output to get range 0-3V proportional out AD8307 outputs 3V dry...
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    Ampop subtractor operational OPAMP amplifier subtractor circuit help

    Thanks a lot for help. Now just need to choose a low power opamp supply from 2,7V to 5V and low current consumption. I think OPA170 or LT1006 - Precision, Single Supply Op Amp will do. Regards - - - Updated - - - I need help to choose resistors. Im using a voltage reference IC 2,5V and and...
  11. V

    Help improve pcb esp12-e xbee form factor

    Help improving pcb esp12-e xbee form factor Hi I need some help to optimize this pcb to fit esp12-e in a xbee form using all io's. See eagle files. **broken link removed** ESP on mirror bottom side xbee form: esp12-e form: Idea is this one. Any help is welcome.
  12. V

    Ampop subtractor operational OPAMP amplifier subtractor circuit help

    Hi, I need to built a circuit to subtract a reference voltage of 4V from a variable signal from 4 to 4,25V This interval 250mV must be amplified 4 times. I need output variable from 0 to 1V Can someone help me designing this circuit and resistor values Any one knows a low power ampop single...
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    AC Wheatsone bridge equivalent impedance at AC

    Now seems I'm working in the dark because my 100MHz oscilloscope is not available anymore.Can't see wave form, but is oscillating at 80MhZ. I'me getting porportional output DC according the impedance of probe. A simple measuring capactitance at probe with capacimeter, 10pF free air and 1000pF...
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    AC Wheatsone bridge equivalent impedance at AC

    Circuit was working at 40Mhz because div connector was open. Now set at 80MHz, voltage output range is going to half. Maybe tantalum capacitors are blocking some 80MHz signal. Dont know why lost voltage range. Now lower interval 300mV instead of 700mV interval dry to wet previosly at 40MHz
  15. V

    AC Wheatsone bridge equivalent impedance at AC

    Hi KamW, I can't call it now bridge because is not a bridge measure. First experiement with one end of probe connected to ground, the voltage only get a difference of about 200mV wet to dry, when changed probe ground pin to other input of amplifier ther circuit started working as I expected but...
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