Translation Board/ Level shifter.

Discussion in 'General Discussion' started by S.Arnold15, Mar 12, 2015.

  1. S.Arnold15

    S.Arnold15 New Member

    Mar 12, 2015
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    Sorry I am noob to this. So maybe this has been already answered. What are you guys, using for changing 3.3v to 5v? I have a couple of Have you guys ever used the Link-sprite T board bridge? Do you think it is compatible? link is below. ... -v2-and-3/

    or do you guys do something else?
  2. fetcher

    fetcher Member

    Mar 9, 2014
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    I use TXS0102 chips for bidirectional level-shifting of the I2C bus, where each pin must be both an input and output. A couple of MOSFETs and pull-up resistors would work, but I wanted something more robust for driving a ~4m cable. The only downside to this chip is it's a tiny surface-mount thing, MUCH smaller than an SOIC-8, rather tedious to solder.

    For 3.3V -> 5V conversion of output-only pins I've used various 74HCTxxx / 54ACTxxx chips I had laying around... e.g. 74HCT04 hex inverter, 54ACT241 octal buffer. The HCT family chips are preferable to normal HC, because their logic-high threshold on the input side is lower. Plain old bipolar TTL, 74LSxxx or just 7404 with no letters in the middle should work too, at the cost of higher power consumption, probably a non-issue for most uses where you only have a few chips.

    On the input side, 5V -> 3.3V, for low-speed signals you can use simple diode (cathode/striped end pointing away from the input pin, allowing the applied signal to pull it down but not up) combined with pull-up resistor on the pin if internal pullups aren't strong enough.

    A more solid option for input shifting, capable of higher speed is the 74HVC245 chip, which will handle 8 pins at once, accepting 5V levels and outputting at 3.3V, 1.8V or whatever you power it with. These are kind of a specialized IC, but can be found cheaply on ebay.

    If you don't want to design your own board, the one you linked to looks OK, except that it handles only a subset of pins, basically the ones present on smaller Arduinos like the Uno, probably since those are the ones 5V-only shields would use, but it looks like it would block other pins on the additional Mega/Due-layout headers.

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