Barometer Pressure Module HOPE HP03

[dhouston]

Or, can the MCU run at, say 20MHz and the 32768Hz be provided to the device from another source?

The I²C clock is usually supplied from a pin on the MCU.

The ratings for the other pins are not given in the spec sheet. Are they '5 Volt tolerant' ?

Not likely. Always assume they are not unless explicitly stated in the datasheet.

[Bill Legge]

DHOUSTON

Thanks for you comments.

1. The normal I2C clock is the SCL pin - and I agree it is driven by the PIC MCU. The 32768 Hz is needed by the MCLK pin and does something for the A to D process.

2. The question of the 5 volt tolerance of the chip - after a day of digging round on the web - seems to agree with your view. Philips has a good application note on bi-directional level shifting for the I2C bus (AN97055). I'll give it a go using 2N7000 MOSFETs

Regards Bill Legge

[Acetronics2]

Hi, Bill

I'd recommend you to have a look to Intersema MS 5534 sensor ...

If the pinout is not the same, internal diagram, functionning principle and features are very-very-very close to the HP 03 ... ( no, i didn't say it ... lol )

Also you will find ANs and tricks on the Intersema site :
http://www.intersema.ch

Alain

[dhouston]

1. The normal I2C clock is the SCL pin - and I agree it is driven by the PIC MCU. The 32768 Hz is needed by the MCLK pin and does something for the A to D process.

In this case I'm sure you can use separate clock sources - there's no reason why the ADC clock would need to be synced with the MCU clock. You can probably use the 16F88's PWM to supply the ADC clock. It would simplify things to run the PIC at 3.3V.

How much does the sensor cost? Where can you buy them?

[Acetronics2]

Hi, Dave

I have a Barometer/Altimeter/Tempmeter/Clock with a 5534, running here ...

The Pic and the sensor are powered from a 3v regulator ( ICL 7663 )
32,7 Khz clock is derived from the PWM module of the PIC ( both 16F876 ( LCD 2x20 ) or 18F452 ( GLCD 122x32 ) projects ... )

The only thing to remember is to have a STRONG Decoupling of the sensor supply : 47µF + Tantalum is recommended for reliable work.

Alain

[Bill Legge]

Thanks for the infirmation.

It seems that the pins are NOT 5 Volt tolerant and I either:

1. Use the bi-directional level converting circuit given in the Philips application note, or
2. Run the MCU at 3 Volts.

Thanks for the idea of using the HPWM signal for the A/D clock.

The HP03 chip (mounted on a carrier with 0.1 inch pins) is available from Ocean Controls here in Australia for about $AUS 25 ($US 20): http://www.oceancontrols.com.au

Thanks Bill Legge

[Bill Legge]

Alain of Acertronics

Alain,

Thanks for your post. Any chance of seeing your program for the 5534. Particularly the I2C comms bit?

I've got mine running but the calibration coefficients are nothing like the published example. I'm wondering if:

1. My code is wrong, or
2. My level conversion is wrong?

Regards Bill Legge
In Australia

[Bill Legge]

Alain of Acertronics

Don't bother with the code - I've just got mine working.

Pull-up resistor on the SCL line was poorly connected.

The bi-directional level conversion described in the Philips application note works fine with a 2N7000 MOSFET.

Regards Bill Legge

[dhouston]

Thanks for the infirmation.

It seems that the pins are NOT 5 Volt tolerant and I either:

1. Use the bi-directional level converting circuit given in the Philips application note, or
2. Run the MCU at 3 Volts.

There are some simpler methods than those in the Philips app note. See Interfacing to Lower Voltage Devices on pp10-11 of http://www.zbasic.net/appNotes/AN213.pdf. The transistor (e.g. 2N3904) circuits of FIG 15 will work for nearly anything.

[BrianT]

I have used hundreds of intersema sensors for atmospheric pressure and 5 - 10 atmosphere applications over the last 5 years. I use a simple resistive divider for the 5>3v3 level conversion. In the 3v3>5 direction I just directly connect.

I run the PIC at 5 volts and the Intersems 5534 at 3v3 from an LDO 3 volt regulator. From PIC to 5534 I have 2k2 with 3k3 to ground at the 5534 end for signals to the 5534 DIn, SClk and MClk. DOut, from the 5534, I just hook directly to the PIC. Yes that means a 3v3 signal into a 5 volt PIC (RC.3). It works.

The HOPE is definitely a knock off of the Intersema product. Has anyone done any side by side accuracy tests? Pricing looks slightly in favour of the HOPE unit but I'm not going to make the change unless the accuracy is at least as good as the Swiss Intersema units.

Cheers
BrianT