sht75 code locked up

[microkam]

i recently complete making PCB board which read humidity and temperature from SHT75 sensor,the board contain DS1307,(PIC16f877@4MHz).
- SHT75 connecting directly to the board through cable sheild 3m long
- the environment is very noisy and the board locate in the panel which contain a power supply and contacter's , some contacter jop is to turn the heater (3-ph,6KW) on and off .

First problem :

i run the system for many hours all things is ok,then the ds1307 start to locking up i solve this problem by code so if the timing is not changed for some time then the cod make a reset for the pic .

Second problem :

all the program is locked up,i add a filter on the input supply 220vac , 100nF, no pin's floating , all things as i think is ok
in the last i found the problem is in the sht75 code , exactly in this code :-
'''''''''''''''''''''''''''''''''''
readsensor:
GoSub tstart
GoSub WaitSensor

ShiftOut dta,clk,1,[cmd\8] ' send command
Input dta ' wait acknowledge
Low clk
While dta=1
Wend
PulsOut clk,10 ' send ack
While dta=0
Wend
While dta=1 ' wait for conversion to complete
Wend
Low clk
ShiftIn dta,clk,0,[result.highbyte\8] ' get first byte
Low dta
PulsOut clk,10 ' send ack
ShiftIn dta,clk,0,[result.lowbyte\8] ' get second byte
Low dta
PulsOut clk,10 ' send ack
ShiftIn dta,clk,0,[chksum\8] ' get third byte (checksum)
High dta
PulsOut clk,10 ' send ack
Input dta ' End of Transmission
Input clk

Return
'''''''''''''''''''''''''''''''''''''''''''''
any one have the same problem .......

[microkam]

can i make a maximum time to wait the data in SHIFTIN,if the data is not received in this time jump to the error label .

[mister_e]

There's no TimeOut facility with Shiftin. I have some doubt on your hardware at first but, if you could use the same setup in a 'normal' environement (let's say on your own bench) and confirm that the problem is still the same, we can probably dig deeper in your stuff.

I see some strange stuff so far... seems to have some missing PAUSE or something, some pins a set Low/High twice, those While/Wend are obscure... If you coulld post your schematic, it could help. Datasheet link, for lazy user like me, could be handy.

[microkam]

thanx mister to try to solve my problem..
i run the board in my lap without heater load and it's run for three days and all things is ok , but the problem start when i connected the heater load , maybe the spark in contacter cause error in the command through sensor cabel sheild , that why the program locked up in the last code i attached .

[mister_e]

Possibles causes:
unsufficient ground plane on your PCB
unsufficient power supply filtering
usused input/output left floating
Ground loop/ground bouncing
unsufficient incoming data filtering/buffering ( can we say buffering ??? ;D )
...
...
...
Is your stuff share a power supply or it have it's own?

You can still additional hardware to Enable and Disable your Contactor on the Zero Crossing of the AC line. It could be done in software too. By using one or the other method, you'll have to adjust the timing to compensate the Contactor latency.

This should solve a part of your problem.

[microkam]

Possibles causes:
unsufficient ground plane on your PCB
unsufficient power supply filtering
usused input/output left floating
Ground loop/ground bouncing
.

the power supply is clean as can be , i put the filter ,the ground plane on my PCB i think is good.

unsufficient incoming data filtering/buffering ( can we say buffering ??? ;D )
.

how can i make filtering for the data incoming from sensor , or how can i solve this problem by code to reset the program if any locked up happend in the sht code.