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RCtime distance between sensing device and propeller — Parallax Forums

RCtime distance between sensing device and propeller

JkaneJkane Posts: 113
edited 2015-04-14 08:18 in Propeller 1
Hello,

I would like to use the HS1101 Humidity Sensor on one of my systems, I have used RCTime before, and if I remember correctly it usually has to be as close as possible to the Pin sensing the delta time (voltage drop). i would like to know if i can build a RCtime PCB that allows a 20 foot distance between the sensing device (HS1101) and the Propeller.

regards

Jeff

Comments

  • tomcrawfordtomcrawford Posts: 1,126
    edited 2015-04-03 09:39
    0. You will absolutely need two wires, signal and ground. Could be twisted pair or coax.
    1. The wires will have a little resistance, small with respect to the 220 ohms shown in Parallax's schematic. Also some capacitance, at one end or the other of the 220 ohm resistor. I don't know whether it is negligible or not.
    2. If you have two Hs1101 sensors, hook up one nice and close; the other at the end of your cable (which is nicely coiled for test purposes) and compare the results.
    2.5 Try putting the resistor at each end of your cable and see which one works best.
    3. Consider using the HS1101 with a 555 to generate a frequency proportional to the humidity. Then remoteness shouldn't be an issue.
    EDIT:
    3.5 If you are using a Propellor and you have a spare cog, think about using an Am2303.
    http://forums.parallax.com/showthread.php/153855-Low-Power-Am2303-DHT22-Driver-for-Propellor
    EndEdit
    4. Be sure and tell us how it worked out.
  • DomanikDomanik Posts: 233
    edited 2015-04-03 11:14
    Tom's #3 sounds good. The HS1101 has a capacitance range of 40pf for 1% to 100%; 20 feet of twisted pair has about 30 - 80 pf depending on?? The capacitance also changes as the wire is bent or moved closer to any ground. Even shielded coax will have these problems.

    A small PCB with the sensor as the control element in an oscillator circuit would work very well. The PCB will require 3 or 4 wires: 1) GND 2) VCC 3) SigOut+ perhaps 4) SigOut-. The datasheet has a circuit to do this.

    At 100KHz it should work remotely to at least 100 feet or even 1,000 feet.
  • kwinnkwinn Posts: 8,697
    edited 2015-04-03 12:48
    + 1 to Tom's #3 suggestion. By far the simplest and most reliable way to go.
  • JkaneJkane Posts: 113
    edited 2015-04-14 08:18
    tomcrawford wrote: »
    0. You will absolutely need two wires, signal and ground. Could be twisted pair or coax.
    1. The wires will have a little resistance, small with respect to the 220 ohms shown in Parallax's schematic. Also some capacitance, at one end or the other of the 220 ohm resistor. I don't know whether it is negligible or not.
    2. If you have two Hs1101 sensors, hook up one nice and close; the other at the end of your cable (which is nicely coiled for test purposes) and compare the results.
    2.5 Try putting the resistor at each end of your cable and see which one works best.
    3. Consider using the HS1101 with a 555 to generate a frequency proportional to the humidity. Then remoteness shouldn't be an issue.
    EDIT:
    3.5 If you are using a Propellor and you have a spare cog, think about using an Am2303.
    http://forums.parallax.com/showthread.php/153855-Low-Power-Am2303-DHT22-Driver-for-Propellor
    EndEdit
    4. Be sure and tell us how it worked out.

    Hello, I am just starting to receive the parts, but in referrence to item 3 in your list

    I was going to build the circuit using a TLC555 timer chip, which is in the data sheet for the Humrel (HS1101), the circuit seems simple and can be fairly small, so I can use my cable (CNC) and I just need to get signal, ground and Vin, when i test it I'll add the results

    (I attached the circuit)

    regards

    Jeff Kane
    HS1101.jpg
    470 x 514 - 38K
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