simple voltage divider circuit

Discussion in 'General Electronics Chat' started by raidermanz, May 12, 2008.

  1. raidermanz

    Thread Starter Active Member

    Aug 14, 2007
    I think I have correctly designed this very simple voltage divider circuit to indicate when a voltage potential reaches a certain level. Since I am an extreme novice, I thought I would ask for constructive criticism. If I am using a PTC device connected with a small resistor in series, I should be able to monitor the voltage between the two to establish the current state of the ptc resistor. Also, using a zener at this point, I should be able to connect that to a pic to be monitored without fear of over-loading the microcontroller. Does anyone disagree with this? All feedback is appreciated.
  2. SgtWookie


    Jul 17, 2007
    What's the resistance range of your positive temperature coefficient thermistor, and the fixed resistor in series with it?

    What is the voltage connected on either ends of the series resistors?

    Please post a schematic; they help a great deal to eliminate confusion.
  3. raidermanz

    Thread Starter Active Member

    Aug 14, 2007
    I apologize for my unforgivable lack of information. I am using a PTC heating element from DBK-USA. This is a temperature limited heating element which they do not seem eager to disclose values on. I guess I am just looking for general guidance rather than specific values for my devices, but what I would like to do is estimate some of the particulars of the design. let's assume that applying 24 VDC to the ptc heating element results in a stable current of 750mA. If the current draw through the heater increases due to cooling the element from it's current temperature, the voltage potential between the ptc and the small value series resistor should increase?? I believe I would need a fairly small valued resistor such as a 1 or 2 ohm to achieve ~2.5 volts at this point. Then I wanted to connect that to a pic microcontroller to monitor this voltage, but in order to protect the microcontroller, I wanted to place a zener in the circuit which could limit the voltage to 5.1 so as not to damage the chip. I hope this makes sense, and I appreciate the help.
  4. nigelwright7557

    AAC Fanatic!

    May 10, 2008
    A resistor of a few K in series with the PIC input will protect it so long as you dont go way over the 5volt rail.
    The PIC has protection diodes on its inputs.