simple 3V serial sensor <=> 5V Pic interface ?

• Mar 5, 2004

• #1

T

tgq

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serial 5v to 3v

hi
i want to connect a 3V serial device to a 5V Pic processor
how can i simply (opencol, opendrain ?) connect
* 3V sensor out to 5V pic in
* 5V pic out to 3V sensor in
Thanks

 

• Mar 5, 2004

• #2

pisoiu

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reduce 5v to 3v resistor

Hi,
* 3V sensor out to 5V pic in
-check if minimum voltage of "1" logic state of output is above minimum input voltage for "1" state of pic . if so, connect them directly. if not, you can use a low treshold voltage mosfet such as BSS138 to connect them. but be carefully, the phase of your signal will be shifted with 180 .
* 5V pic out to 3V sensor in
-if the speed is not high ( up to hundreds khz) you can use a rezistive voltage divider to adapt "1" logic level from 5v to 3v.

 

• Mar 5, 2004

• #3

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revolt

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connecting sensors to pic24

the best way is to use a level translator.
e.g. MAX3001E from maxim

 

• Mar 5, 2004

• #4

C

C-Man

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5v to 3v serial

hi tgq

check if your sensor can accept 5V input signals (most 3.3V logic can) if yes you can simply connect the 5V output to the 3.3V input.

Also simply connect your 3.3V output to the pic input without a level converter, this should work almost always ...

If not you need a simple level converter. I have posted a self built one a few days ago, simply check my posts.

best regards

 

• Mar 5, 2004

• #5

T

tgq

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3.3v 5v bs170

hi all
i 'cross-checked' before my question the different H/L voltages :
* the 3.3V serial sensor has not enough H level out for the pic input
* the sensor in cannot accept 5V
Cman thanks i found your picture, but i thought about just a simple BS170 + drain resistor to build the level converters

 

• Mar 5, 2004

• #6

C

cancel

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getting sensor inputs from 3v to 5v

i saw some app notes like this.
pull up 3v input to 3v vcc, connect it to 5v pic output via diode (kathode to pic)

 

• Mar 8, 2004

• #7

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Ajay

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bs170 5v to 3.3v

we have used 5 V 232/485 drivers to our 3 V systems using simple resistor dividers. As C-man said before, it should be no problem to connect the 3 V output to a 5 V input system since 3 V is considered as logic high. However, connecting a 5 V output to a 3 V input system can be bad news. There simple resistor dividers can do the trick.

Ajay

 

• Mar 8, 2004

• #8

T

tgq

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5v to 3v logic converter

Ajay said:

it should be no problem to connect the 3 V output to a 5 V input system since 3 V is considered as logic high
Ajay

Click to expand...

hi
thats not so simple, some 3V devices cannot supply more than 70% Vdd, this can be too low for some 5V inputs, eg in my case with PIC High minimum input level

 

• Mar 9, 2004

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dingding123

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5v input to 3v processor

5V to 3.3V 74LCXxxx(or 74LVXxxx)
low voltage with 5V tolerant input
3.3V to 5V usually you can connect it directly to
5V CMOS or TTL input pin

 

• Mar 10, 2004

• #10

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Ajay

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bss138 serial

tgq said:

Ajay said:

it should be no problem to connect the 3 V output to a 5 V input system since 3 V is considered as logic high
Ajay

Click to expand...

hi
thats not so simple, some 3V devices cannot supply more than 70% Vdd, this can be too low for some 5V inputs, eg in my case with PIC High minimum input level

Click to expand...

Are you saying that the pull up on your sensor is very weak? It puts out about 2.1 V as high and 0.6 as low. Well, I would worry about noise margins in that case. Why is the pull up so weak on the sensor?

Ajay

 

• Mar 11, 2004

• #11

T

tgq

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how to reduce 5v to 3v

ask the constructor :lol:
more seriously, i can increase the sensor voltage near its maximum, so i can get the guaranteed minimum output for the PIC minimum input
fortunately the device is not in a noisy environment

 

• Mar 14, 2004

• #12

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xxtigerxx

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5v to 3vzener

a cheap solution is

from 5 to 3 with a zener 3.2V and a resitor in series.

from 3 to 5 you can use a bjt trnastor in on-off condition driver by 5volts

 

• Mar 14, 2004

• #13

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raticus

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level converter bss138

The most cost-effective solution to reduce 5v to 3v logic is

5v---{4k7 and 47pf in parallel}---3v

It works perfectly.