@AWI - looking at parallel so I can process data faster ... I can't save to pc at a rate fast enough to keep up with sampling rate.

I have built a few projects using a few different 3 axis accelerometers, such as the LSM303DLHC. All of them used the i2c interface.

I'm wondering if anyone knows of a somewhat similar device that can be connected to a microcontroller via a parallel (eg: 8 bit) interface ?

I've now tried various algorithms.

In all of these I set the oversampling of both temperature and pressure to 1 (no oversampling).

1. Forced mode, with fixed 5mS delay between reads,

2. Forced mode, with fixed 4mS delay between reads,

3. Forced mode, with fixed 3mS delay between reads,

4. Forced mode, with fixed 1mS delay between reads,

5. Normal mode, set t_sb = 0.5 mS, waiting until status bit 3 = 0, read data, repeat

6. Normal mode, set t_sb = 0.5 mS, waiting until status bit 3 = 0, read data, wait until status bit 3 = 1, repeat

With each algorithm, I'd do 2000 reads.

As I went through the above scenarios, the minimum and maximum readings (for both values) got farther and farter apart - ie: the range of values got larger.

That was until #5, where it was slightly better then #1. The range with #6 was the least of all - in other words, algorithm 6 gave the most consistent readings (I should say the sensor is laying still throughout these tests).

In #5, it took 6 seconds to make 2000 readings - or an ODR of about 333 hz. In #6, it took 12 seconds to make 2000 readings - or an ODR of 166 hz. Just what the datasheet said would be the maximum ODR.

I have to assume with #5, about half the readings were done before the registers were updated. In other words, it was a waste of cpu time to make the reading.

I am using a BMP280 module. I am very confident my system setup and software are working fine. Readings of temperature and pressure I receive seem valid.

I wish to implement a design, based around an 8051 microcontroller, where the pressure reading is continually read from the device and sent out a serial port onto my PC where it is date stamped and saved to a log file.

I want to run this as fast as possible. I do not wish to use the IIR filer, as I actually want to see any spikes that might appear.

I'd be just reading the 3 or 6 bytes (either just pressure or pressure and temperature) and transmitting the raw values to my PC (converting later on). I've had my circuit reading 11 bytes from a different I2C sensor, and transmitting those values, at 800 hz without problems. So I know I can handle the fastest ODR the device claims to achieve.

I understand I can either run in "forced mode" or "normal mode".

It is not exactly clear to me which to use.

Also, regardless of the mode I use, how would I know when to read from the device ?

If I run in forced mode, can I simply write my code to run a tight loop of just reading from the device, transmitting the data to my PC, over and over ??? It would seem I would be trying to read at a rate that is much faster then the device can actually handle. Is there a problem with that ... as in ... would I risk reading invalid data ?

If I run in normal mode, there is some sort of standby time. Would I need to determine that time, and write my code to wait AT LEAST that amount of time before seeking another reading ?

Your help would be greatly appreciated.

I have a few HC-SR501 sensors and have not seen any of them function. I connect 5v and gnd to the 3 pin connector, and monitor the output via multiple means. I point the sensor in various directions, and never see it change. I vary the pots, the jumper. Nothing changes.

Please trust I have not been sitting at a bench with the sensor pointing at me all the time I am not using any other circuit at this point, just 5 Vdc, logic probe, scope, etc.

Can someone suggest how to initially set up the HC-SR501 ?