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polulu ir beacon level shift — Parallax Forums

polulu ir beacon level shift

stargazer2050stargazer2050 Posts: 89
edited 2014-01-25 08:01 in Propeller 1
Polulu ir beacon
Quickstart bd
Bs170
Nte3220
Voltage divider

Has anyone sucessfully level shifted beacon to 3.3 v?
Tried three methods so far getting strange results.

Comments

  • Duane DegnDuane Degn Posts: 10,588
    edited 2014-01-23 12:55
    stargazer2050 wrote: »
    Has anyone sucessfully level shifted beacon to 3.3 v?

    I'm pretty sure the answer to this is yes.

    Assuming the Pololu beacon outputs 5V (a link would be nice), then all you should need is a 10K (or 3.3K ior 4.7K) resistor to keep the current on the input pin below 500uA.
  • stargazer2050stargazer2050 Posts: 89
    edited 2014-01-23 13:21
    Hi duane!

    http://www.pololu.com/product/701
    5.6k over 10k gives me 3.2 volts at 320 ua.
    I metered it also. However when i put the output into the propeller, it lights up each of the ir leds to which they are attached.
    When i increase to 56k over 100k they no longer light up but they stop working.

    Too little current maybe?
  • Duane DegnDuane Degn Posts: 10,588
    edited 2014-01-23 13:47
    You don't need a voltage divider. As long as you have at least 3K ohm in series between 5V output and Prop you're okay. The Prop pins have clamping diodes but they can only tolerate 500uA (0.5mA) of current.
  • stargazer2050stargazer2050 Posts: 89
    edited 2014-01-23 13:59
    Min 3k in series ... Im on it.

    And again i thank u.
  • JonnyMacJonnyMac Posts: 9,107
    edited 2014-01-25 08:01
    I agree with Duane; it appears the outputs are driven high and low to control the detection LEDs. Put a 3.3K resistor in series with the outputs and take them into the Propeller.

    Why 3.3K? It's the nearest standard value to 2.8K which is the calculated minimum one should use to protect the Propeller pins from a 5v signal. Easy to remember, too: 3.3v Propeller uses 3.3K resistor to protect inputs from TTL circuits.
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