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Re: [Paparazzi-devel] i2c voltage level

From: Refik Sever
Subject: Re: [Paparazzi-devel] i2c voltage level
Date: Tue, 20 Aug 2013 00:12:57 +0300

Hi Martin and Heinrich,

Thank you very much for your replies.

I understand that drotek i2c signals are using 3.3v, therefore no problem for 

I also want to add SRF08 ultrasonic sensor to the other I2C bus. SRF08 works 
with 5V, and I2C signals are also at 5V. On the same bus, I also connected 
TMP102 temp. sensor and ETS airspeed sensor. They all use 3.3V i2c signals, and 
they all get their supply from autopilot.

I understand from your emails that digital i/o pins of LPC2148/stm32 are 5V 
compatible, therefore no problem for the autopilot. Will there be a problem for 
tmp102 and ets airspeed sensors?

Best regards,

>From: address@hidden [mailto:address@hidden On Behalf Of Prof. Dr.-Ing. 
>Heinrich >Warmers
>Sent: Monday, August 19, 2013 6:00 PM
To: address@hidden
Subject: Re: [Paparazzi-devel] i2c voltage level

if you supply the imu with 3.3V it works with 3V i2c.
If you supply it with 5V it works with 5V i2c.
But you may destroy the 3V i2c components if you connect them with 5V i2c.
The lpc2148 is 5V compatible if it is supplied with 3.3V.
If you power on the i2c brush less controller (5V)  and the lpc2148 has no 
power you will destroy the LPC2148.
The stm32 pins are only 5V compatible if the processor is supplied.
The maximum level is 4V if there is no power on the processor.

-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of Martin Mueller
Sent: Monday, August 19, 2013 6:24 PM
To: address@hidden
Subject: Re: [Paparazzi-devel] i2c voltage level

Hi Refik,

> We have bought Drotek 10dof IMU, and the module works with 5V.  Do the 
> I2C pins of drotek also work with 5V?

the board is supplied with 5V but the sensors run on 3.3V and so do the I2C 
lines. An on-board linear 5V -> 3.3V regulator is used to have a clean 3.3V 
supply (see imu-10dof-mpu6050-hmc5883-ms5611.PDF).

> Are the I2C pins of LPC2148 and STM32 processors compatible with 5V?

The digital LPC2148/STM32 pins are claimed to be 5V tolerant (not the LPC ADC 
input pins) but it is good practice not to run them at 5V.

Never apply a voltage to any pin of a chip that is not powered through the 
supply voltage.


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