Computer Display?

[HenrikOlsson]

Hi Ed,
A link to the datasheet for the sensor in question, or at least a part number would be a good idea to post. Somehow Norm knew or assumed its output was RS232, something you didn't say in your first post, so my question is: Is it?

If the sensor is indeed outputting async serial it may be doing so at TTL levels and your PC may not like that (even though it usually works for short distances) so you may need a MAX232 driver or something.

A diagram showing how you have it connected would be nice as well.

But again, without even knowing what type of sensor you're talking about it's just guesses.

/Henrik.

[Ramius]

Hi Henrik!
The sensor is the infamous MS5541-CM and I believe the protocol is SPI. Basically the sensor to a 3v to 5v converter to the PIC then from the PIC to a MAX232-cpe to the computer. At short distances from the 3-5v converter the sensor readings are "normal", that is you will accurately read room temperature for example. As the cable from the 3-5v converter becomes longer the room temperature reading becomes abnormal such as -1434C. First cable was a shielded 6-wire, 22 gauge cable. Then I tried a ribbon cable with signals on every other wire with ground at one end only for the wires inbetween the signal wires to avoid cross talk and any ground loops.

Best, Ed

[HenrikOlsson]

Hi Ed,
OK, so the problem is not with the cable to the PC then....

More questions:
1) The sensor needs an external clock of 32.768kHz (typically), how are you feeding it that clock signal? Thru the same cable?
2) The maximum SPI clock frequency (not the same as above) is 500kHz, what frequency are you using and are you using the MSSP module in the PIC or SHIFTIN/SHIFTOUT?

Again, a diagram showing what you have and exactly how it's connected really does make it a lot easier when trying to help. What's that 3-5V converter for example?

/Henrik.

[Normnet]

Ramius

If it's the RS232 cable to the PC you are trying to lengthen try setting the RS232 baud rate slower.
As a rule reliability goes up when the baud rate is slower.

Norm

[rsocor01]

Ed,

Sometimes that 3v/5v converter for the communication lines are not needed. Are you converting the SPI lines to 3v going into the sensor? For a long cable there are already losses. Try your setup without the DC/ DC converter.

Robert

[Normnet]

Ed,

Sometimes that 3v/5v converter for the communication lines are not needed. Are you converting the SPI lines to 3v going into the sensor? For a long cable there are already losses. Try your setup without the DC/ DC converter.

Robert

A 5 volt pullup resistor also can help when not using a 3v/5v converter.

Norm

[Ramius]

Hi All!
Basically the sensor goes into a TXB0104 at 3v and from the TXB0104 at 5v into the PIC. I have been trying to extend the 5v side from the TXB0104 to/from the PIC with Shiftin and Shiftout. This has clearly been a problem for others after several hours of searching the internet and no one seems to have published a solution. From the PIC 18F1320 through a MAX232CPE into Com1 using the ICD in PicBasic Pro you can see all the readings. While very difficult to do I did manage to place a 47mfd tant. cap to the back of the sensor so it could not be any closer/shorter! Attached is the drawing. Ed