Getting 3.3V from 5V

[ilan1]

I'm building a circuit in which I am going to interface a bluetooth module to a 16f628a. The module runs on 3.3V and not on 5V and because it is a relatively expensive module, I don't want to burn it up or mess it up by applying 5V to it.

Can somebody clue me in on how to do this exactly? Am I supposed to use a diode of some kind? If somebody could tell me a part #, sample schematic and general theory, I would be most appreciative.

Thanks!

Ilan

 

[Nigel Goodwin]

I'm building a circuit in which I am going to interface a bluetooth module to a 16f628a. The module runs on 3.3V and not on 5V and because it is a relatively expensive module, I don't want to burn it up or mess it up by applying 5V to it.

Can somebody clue me in on how to do this exactly? Am I supposed to use a diode of some kind? If somebody could tell me a part #, sample schematic and general theory, I would be most appreciative.

The PIC will happily accept a 3.3V logic input, the other way a simple current limiting resistor may be all that's required?, depending if the module input has protection diodes like a PIC?. Failing that, use an open-collector buffer to feed the module, with the pullup resistor connected to the 3.3V rail (you can use RA4 from the PIC, it's an open-collector output).

You might have a look at my radio PIC tutorial, which does much the same thing!.

 

[hantto]

Or feed the PIC of the 3.3V rail.

 

[Oznog]

But the 5v output from a PIC running at 5v shouldn't be fed into the 3.3v module unless the module says this is ok.

PICs- at least the ones I have- can run off 3.3v. There are limitations when doing so, for one, the max frequency it can be run at may be reduced. Check your part's spec sheet.

 

[Someone Electro]

A PIC should run no problem off 3.3V.You can still run it at max freq. but the PIC is more likely to make an error.(the chanses are still vvveeeerrrryyyyy slim)

A guy ran an PIC16F at 32Mhz and it worked whithout an error in a 2 hour test.

 

[Matt(Pic progger)]

5 -> 3.3V

Hello, a qucik and dirty logic "converter" can be made using a Red LED the LED will drop approx 2V across it and give your logic level as 3.3V

You can also use the above technique to get a cheap/desperate 3.3V supply from a 5V source, just remember that you will only be able to pull about 20MA from this "solution" before the led will be destroyed.

With both of the above CHECK THE VOLTAGE FIRST BEFORE POWERING UP YOUR 3.3V device.

Oh, 1 more thing, if you use an LED as a level shifter the the micro (PIC) will not be able to read a logic high from the device, as an LED is a diode, but you can "send" data to a device in this manner.

Hope this helps, and don't call me if u nuke ur device!