3.3v signals to 5v signals

[InitialDriveGTR]

Hi, can I use pull-ups to allow the PIC to properly receive the 3.3v signals from a SPI Radio module? Thanks

[mat janssen]

No, you have to build a level converter to convert your signal from 3.3 to 5 volt.(possible with 1 transistor)

[mister_e]

3.3 v could be enough to be considered as a high level signal. Maybe you could just use it without anything in between. Depending your PIC, you could also use the built-in comparator and use it as a level converter as well.

[keithdoxey]

3.3 v could be enough to be considered as a high level signal. Maybe you could just use it without anything in between. Depending your PIC, you could also use the built-in comparator and use it as a level converter as well.

I have a USB Serial module that I use with my PIC projects.
http://www.dontronics-shop.com/produ...roductid=16141

That has 3.3V lines for TX and RX. I just use a 1k resistor between that and the PIC and it works fine

If you were only going from the 3.3v device to an input then direct connection would probably be OK but if you send any signals back from the PIC then without a limiting resistor it would probably damage the 3.3v device.

[InitialDriveGTR]

I tried your schematic, and all it does is cause my PIC to reset, and directly connecting just reads in jibberish

[Ron Marcus]

I use 5 volt PICs and 3 volt PICs or other devices together all the time. Never had an issue as long as a resistor was put between them. (1 to 10K).

[InitialDriveGTR]

That is true, but my problem is that the PIC is looking for 5v signals, and the radio module is only supplying 3.3v signals, so the PIC doesn't properly read the module's output.

[Ron Marcus]

Depending on the PIC and port pin, a "1" will be any voltage over 1.8 to 2 volts. 3.3 will look like a "1", not a "0". If the PIC is not seeing a "1", something else is wrong. Check the "Tris registers, and if you want to prove the trip point of the PIC yourself, hook a 10K potentiometer to B+ and ground.Next hook the wiper to the pin in question. Write a short program to turn on a LED when the pin goes positive(and off when a zero).Next, measure the voltage.If it's over 3 volts, I'll buy the coffee!

[dhouston]

At least on the PICs I use the hardware SPI pins have Schmidt Trigger buffers and need 0.7*Vcc (3.5V @ 5V) for a logic high.

[Luciano]

Hi,

Some links.

Best regards,

Luciano

Interfacing 3V and 5V applications:
http://www.semiconductors.philips.co...otes/AN240.pdf

Voltage Level Conversion:
http://focus.ti.com/lit/an/swra071/swra071.pdf

* * *
5V to 3.3V and back from 3.3V to 5V
(Works down to 1.5V)

74LVC4245A Octal dual supply translating transceiver; 3-state
http://www.semiconductors.philips.co...LVC4245A_5.pdf

MAX3370/MAX3371 logic level translators
http://pdfserv.maxim-ic.com/en/ds/MAX3370-MAX3371.pdf

More level translators from Maxim:
http://para.maxim-ic.com/cache/en/results/5043.html

* * *

5V to 3.3V
Inputs can be driven from either 3.3 or 5 V devices.
(The 74LVC125A and 74LVC244A will not replace the 74LVC4245A or the MAX3370/MAX337).

74LVC125A:
http://www.semiconductors.philips.co...4LVC125A_4.pdf

74LVC244A:
http://www.semiconductors.philips.co...LVCH244A_4.pdf

[InitialDriveGTR]

Ok, I successfully got it to receive data using a LVC chip. Now, I have a GPS (CW20 from Navsync - email them for free samples - you just need an antenna) and it has a very vague data sheet. My oscilloscope says it is operating it's serial output at 1.8v. How do i get the PIC to see that? I think a loop back with a max233 might work

[Luciano]

Hi,

Use that:

MAX3370/MAX3371 logic level translators
http://pdfserv.maxim-ic.com/en/ds/MAX3370-MAX3371.pdf

The devices accept VCC from +2.5V to +5.5V
and VL from +1.6V to +5.5V, allowing data transfer
between low-voltage ASICs andhigher voltage devices.

Best regards,

Luciano

[InitialDriveGTR]

Wow, thanks for your help all