SHT15,MPX4115A and external pulse counter with PIC16F72

[PCM programmer]

You can just mention the CCS forum. A lot of people give help.

[stijn023]

Ok I will do.

[stijn023]

Does anyone know the lifetime of a reed relays?

thanks in advance.

[PCM programmer]

This is a Google question. Search for this:

[stijn023]

thanks for replying

[stijn023]

Hi,

i have a problem.
I built everything in but the SHT15 doesn't work anymore.
I connected it with a cable of 15 m and I get readings for temperature of -39.9°C and for humidity of -4.6%.
Is there a problem with the length of the cable or have I connected the SHT15 wrong?

Thanks for replying.

[Ttelmah]

#1, cable.
What is the capacitance of 15m of your cable?.

Best Wishes

[stijn023]

I don't have the equipment for measuring the capacitance of a cable.

Thanks for replying.

[stijn023]

Maybe I can use the P82715 I2C bus extender but will this work with a clock frequency of 4 MHz?

Thanks for replying

[Ttelmah]

You don't need equipment. Get the specifications of your cable....
Data is your friend.

Best Wishes

[stijn023]

I've got an UTP cable of 3 meters.

[temtronic]

I've got some 40 year old reed relays still working.they have hard gold plated contacts in them,I think,been quite awhile since I needed to service the device. Trick with reeds is to NEVER put excessive curent through them, even once !

As for your 3M UTP cable, that isn't saying much, spec-wise.
Who mae the cable, what are their specs?
What does the mfr of the SHT15 sensor require for cabling ?
What are the specs for the I2C section of the PIC.
What are you using for connections? Gold plated RJ-45 or tinned?
Is this a PCB, 'solderless breadboard',perfboard ?

Do a real test,keep cutting the cable shorter until it works though a little reading might save you some time,you'll remember what you found out !

[Ttelmah]

The big question on twisted pair, is how you are using the pairs?. The signals you are sending, are _not_ really designed for twisted pair transmission. Twisted pair cable, is designed to be driven with quite a low impedance driver, driving differential signals, into the wire pair (50R). Now the SHT15, in it's data sheet, gives a maximum recommended capacitance of 100pF. (I2C, at lower speeds allows up to 400pF). If you are driving the signal wires into one wire of a pair, with the other perhaps connected to ground, the typical capacitance of this cable, is 5500pF/100m, giving a maximum useable length, of about 2m!...
Change your cable. This signal is not designed for TP transmission. A shielded cable for each signal, with the shields grounded, should reliably give you 3m, and 10m is 'possible', but really long distances will require a transceiver.

Best Wishes

[stijn023]