Any idea to make the old sensors compatible with 3.3V teensy 3.6?

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mrmu

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Hi I have been playing with arduino for a while, so have some 5V sensor/motor driver around. Some of them were designed for arduino and don't have their specification. I assume they have to work at 5V. I can have seperate power supply for them but for other lines like signal i2c sda scl, should I put resisters between those pins and ground to divide the voltage? Any better idea?
 
The best way to translating signal from 5V to 3.3V depends on the type of signals.

For SDA and SCL (the I2C communication signals), these level shifters are best.

https://www.sparkfun.com/products/12009

For other types of signals, "it depends". That type of level shifter works very well for I2C, but it performs poorly for fast signals like SPI and WS2812 LEDs. If you want advice about other signals, you're going to have to mention more. This is the best advice I can give for the signals you said.
 
Many circuits specified to run on 5V will run just fine on 3.3V, so I'd say that would be first thing to try.

If there are some that really need 5V for proper operation (electric motors, for example) there are a number of ways to interface them to a 3.3V micro, but as Paul was already asking for it, you need too provide more details on the exact devices you have.
 
Many circuits specified to run on 5V will run just fine on 3.3V, so I'd say that would be first thing to try.

Be very careful when trying. If the device is powered by 3.3V it's more or less safe to try. If it is powered by 5V it will most likely drive signals to a logic high voltage of near 5V, which is too much for the Teensy 3.6. It would be better to use a Teensy with 5V-tolerant digital inputs such as the Teensy 3.5 or 3.2.

To complicate things further, if the only connection to the Teensy is a I2C bus, this might still be safe with a Teensy 3.6 and a 5V-powered device, because I2C uses passive pullups. You need to make sure there are no pullups soldered on the device to its 5V supply rail and you should use discrete pullups to 3.3V

Series resistors or voltage dividers may or may not work, this mainly depends on signal integrity requirements, so it's dependent on signal speed, cable length and so on.

As you can see, there's a lot to take care of when coupling devices of different voltage domains. We can help you better the more specific your question and the more information (schematics, datasheets, pictures) you provide.

Ben
 
Thanks Paul, I do have some SPI and CAN module (with mcp2515 tja1050 on it) and it would be nice if the converter can also handle uart. I found some 8-channel TXS0108E and 74LVC8T245 modules, looks like the TXS0108E is better in terms of speed? I don't think current is a problem.
 
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