Re: [Paparazzi-devel] i2c voltage level

[Martin Mueller]

Hi Refik,

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

Yes. Add a 5V <-> 3.3V level shifter for the SRF08, see the TEMOD module 
for an example

http://paparazzi.enac.fr/wiki/Module/Hygrosens_TEMOD-I2C-R1

Martin

> Best regards,
> Refik
>
> > 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
>
> Hi,
> 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.
> Heinrich
>
> -----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.
>
> Martin
>
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