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Reflective Object Sensor for Propeller Chip — Parallax Forums

Reflective Object Sensor for Propeller Chip

idbruceidbruce Posts: 6,197
edited 2010-10-31 08:54 in Propeller 1
Hello All

It has been a long time since I have been here, I hope everyone is well. Anyhow I am trying to adapt a Basic Stamp example to the Propeller. One of the examples given in the Process Control text, is an example of using a QRB1114 Reflective Object Sensor. In succeeding Errata to Process Control, it is recommended to change both the emitter and sensor resistors to 1K ohms and to place a 220 ohm resistor before the input pin. In the Process Contol example, VDD would have been 5VDC, so it is my intention to feed both the emitter and the sensor with a regulated 5VDC from the Propeller Proto board. I have been told that since I am returning 5VDC instead 3.3VDC to the Propeller IO pin, I should substitute the 220 ohm resistor for a 10K ohm resistor to bring down the current and protect the IO diode. Is this correct and does the schematic look like it would work like it should? I have attached the proposed schematic and the necessary datasheet. Any input will be greatly appreciated.

Bruce

Comments

  • W9GFOW9GFO Posts: 4,010
    edited 2010-10-30 17:44
    Is there a reason that you don't want to just use 3.3 volts?

    Rich H
  • idbruceidbruce Posts: 6,197
    edited 2010-10-30 17:57
    Rich

    There's really no reason that I could not use 3.3VDC, except for the current layout that I have on the proto board, however it is still adaptable. I truly just want a dependable circuit. I have a working 5VDC circuit, but it was arranged with hit and miss resistor values. I am much better at programming than electronics, and since I am working on a new proto board, I am just seeking guidance for dependable circuitry.

    Bruce
  • idbruceidbruce Posts: 6,197
    edited 2010-10-31 01:27
    Here is a schematic of my existing circuit and it appears to be working perfectly well for my particular purpose. I suppose my question should be, "Is the IO pin of Propeller chip sufficiently protected from overcurrent in the circuit below?
  • idbruceidbruce Posts: 6,197
    edited 2010-10-31 03:22
    OOOOpppsss

    I apologize, I am currently feeding that circuit with 3.3V. SORRY
  • kwinnkwinn Posts: 8,697
    edited 2010-10-31 08:54
    That circuit is fine for the prop with a 3.3V input. The led current will be pretty low with a 1K resistor and 3.3V in so I am a little surprised it works. A typical current limiting resistor would probably be in the 180 to 240 ohm range to provide 5 to 10 mA to the led.
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