Sensors

thanks fr ur suggestions amit.....

m using the same AT89S52 uC... abt HIH4000...i'll ask my H.O.D if they cud provide me any help...... m tyring fr another sensor in the market aswell....

n yes ... i checked rob faludi's soil moisture circuit.... the same ws used by u..i'll be trying it on monday...

i tested the temperature sensor ckt used in GREEN BEE project.. it had lm35 as temp sensor and lm324 to amplify the o/p.. the voltage dint rise if i increased the temp arnd the sensor...

then i used the temp smsr ckt given in mazidi. it .. gt the desired output.. this ckt is given fr adc0848... the adc m using is 0809....can i replace adc0848 with 0809 n use the sensor ckt given in mazidi??
dont knw abt 0848

n one more thing... m nt getting ny gud ADC tutorial... can ny one send me the link fr tht??

Could you tell me what th eissue is that you are facing with the circuit? Well, you can use the LM35 directly with the ADC just like its done in Mazidi, but you will have to deal with some practical issues. The basic reason why we used LM324 was to amplify the o/p of the LM35. Now you can use any op-amp (fir eg. uA741) for this but we had a terri8ble time blowing up circuits to generate + and -5 V and maintain a common ground! LM324 doesnt need a -5V referance. You could use any op amp that gives you this advantage.

You could entirely eliminate the amp, but you will notice that your calculations need to be very precise then cos the variations will become very small. Amplifying the signal does give you some ease and peace of mind.

Coming to th eerror to the circuit, just check if the pins are right with the datasheet. (i.e. th ei/p, o/p, ref. signal, etc.) Some small error may have crept in cos the documentation was done in a hurry and frankly I did not spend much time verifying what went into it and gave it a cursory glance.

You can use the ADC tutorial on thi sforum by Ajay, it is quite good and also try one by "Mahesh Wankhede" www.freewebs.com/maheshwankhede/ a very useful link...

hii amit..
yes... thr is an error in lm324 pin connection.. the vcc and grnd wr swapped...
i connected the ckt correctly... bt initially m getting .28v... (at room temp.. whc is appprox 28 c).. if i increase the temp.. the voltage does nt increase..
thts why i switched over to ckt in mazidi.. this ckt is givin exact outputs.. at every degree rise in temp.. thrs an increase of 10 mv..
at 28degree C- .28 V, at 29degree C- .29 V n so on....the reference voltage i gv ws 5V...

n regarding ADC tutorial... thanks a lot fr suggesting..

u used IC 4083 -a schmitt trigger nand gate for generating clock fr ADC.. nt getting this IC..
i think the IC is nt 4083.. it shud be MC14093BF : Quad 2-Input NAND Schmitt Trigger..thts wat i gt wen i googled fr it..if its nt taking much of ur time.. will u pls confirm this n tell me???
thanks once again!!!!! :-)

Read the mahesh wankhde turorial. I think he has explained why an amp is useful. You will be able to show better variations for starters. Also ease in making a lookup tabl and calculations. A gain of 5 is what I had used. 10 would be too high i think.

The IC is correct. I think it should be 4093 not 4083, could u pls confirm. I had taken it from the National Semiconductors book(mentioned in the bibliography) The IC was available here and the circuit was one of the sample circuits of that IC mentioned in that book. U can check out with that IC u mentioned if it aint too expensive. I remember a friend mentioning that he used the 74HS.. series instead of 74LC.. for the clocking. You can use any clock circuit. Basically u should be able to generate a clk freq in the desired range and it should not be very noisy and as sharp as possible, so go in for a HS (hihg speed) or schmitt trigg gate. We spent many days on getting the exact RC combo for that ckt and had to use DRBs and capacitance bokes and some other kit to give and exact RC combination. Try searching on the net or taking some one more experienced than me here. Ajay, Pdi, sashi or anyone should be able to solve this minor glitch.

Am sorry for the delayed reply and typos. Am a bit busy as I am in the process of applying for my MS. I am online daily but just dont get the time to respond immediately...

Good luck and do tell me how it goes. What happened about the HIH4000 and the moisture sensr?

moisture sensor is working perfectly !dance...getting the desired results... thanks fr ur valuable suggestions.. :-)
abt humidity.. hv dropped it.. nt using the parameter.. cllg is not supportive..:(

by the way all the best fr ur MS.. applying fr this fall??? whc university? no problem at all for delay..

monday will be the last working day fr the project... will continue it in next sem i.e frm feb.. i hv my end sems in nxt month...

Oh thats good and bad news! Are they happy with just 3 parameters then? Well in that case you could try modifying it and trying some more ad-ons to the set up!

Thanks a ton for your best wishes. Yes I am applying this fall for embedded systems and VLSI. Screwed up my GRE Verbal score but got good TOEFL so hoping I get some leeway. Still undecided on all univs am applying to. Everything is in a volatile state and all together its getting in my nerves :mad

Well, I see that you have an entire sem left to complete the project so you have enough time and could most certainly extend the project. I would love to see some improvemnts :-)

Good luck with the exams