ohm meter circuit with 8051

[desmond]

anyways......thx for yr help..^^

 

[karesz]

Hi Desmond,
I hope, these is what you can good adapt to your 8051& ADC0804...

 

[desmond]

Hi karesz,

Thx very much...................i will follow yr circuit tmr...............very thx.....i hope this can help me to read the value from 0V to around 5V ^^

 

[desmond]

Hi karesz,

i have a few of quesions.

1. my adc0804 Vin is 0V and ref/2 is around 3V at the beginning...does anything wrong ???

2. if i use 10k ohm for P1, is it ok ???

3. we no need to connect 5V to force sensor ???

4. what pin should i check for the voltage ???

i really have many problem about your design ......sorry for that

 

[desmond]

Hi karesz,

I have connected to yr circuit twice, but it seems cant work....
plx help

 

[karesz]

Hi,
sorry, I was outside today...
1, how is your Uref realized pls?
My idea was: you has either the LM 336 or ZD2.4 (to U3/4 you need R7, but dont need R5/6 & P3) or even the resistor-poti chain (for that option you need R6/7+P3, but dont need U3/4 + R7 & P2!!)...
2, You can use it, but w. 10K will be the unwished variance of Gain higher; datasheet propose max. 1/20 of R3(150K)...
3, I think; is better if you supply it from stabilized_if you didnt selected the "poormans version"_(buffered 2.5V Uref)...

4; Check pls first your Uref!
5, Take the R9 from Op and control the ADC with a DC voltage_per some potenciometer_ Check for ADC function....

6, You can (& I believe; you must do it!)check the Forcemeter as standalone circuit too!
7, apply the R1 to your Uref(+2.5 or ev. 5V for the tests) & do offset setting for (more or less) zero Uout with zero force on the sensor.
8, Apply some force(i.e. 1kg sugar onto,check for the Uout; it must be some at ~2V(sorry I dont have yet the datasheet of them). Better is to apply the desired full range in kg to the sensor_maybe you will measure up to 10 kg, than do a weight of 10kg on the sensor and check for full range Uot of i.e. 4.5V, you will need surly some justage on the gain resistor values; becouse the sensor has very big variances (up to +/-25%) & maybe you dont wish to use it in the full range_these is your deciding & knowlidge...
Of course: you can do/apply instead of the sensor i.e. a 20/50K Ohm _in force values calibrated/scaled_potentiometer (is excellent methode, than has a "zero value" of ca. 1%=300-500Ohm, as the sensor too) and check the Uout with different poti positions...
Good luck!
K.

 

[desmond]

Hi karesz

as u said...........i just

1. my Uref is around 1.7V at forceless........n no change when apply the force

2. i just connect U4, R7 without R5, R6, P3, P2 n U3......am i correct ???

thx a lot

Added after 10 minutes:

also...

1. when i connect U3, P2, R7 without R5, R6, P3, U4

the Vmax is 1.9V and Vmin is 0.7V

2. the same......the voltage is no change when apply force on it

help

Added after 43 minutes:

also

1. if i just connect R5, R6 & P3 without R7, U4, U3 & P2

the range is from 1.66V to 2.9V

2. the same......the voltage is no change when apply force on it

 

[karesz]

Hi,
Sorry, where are you measuring the Uref & the voltage that isnt changed pls?
K.

Added after 4 minutes:

Ohh!
I think Uref problem is my mistake_sorry!
Put the Uref buffer,U1B, pls between the Ref circuit & rest of circuit(practically under U2 on schema)...

 

[desmond]

Hi Karesz

I havetried yr updated version...
it seems still dun work.......

help again

Added after 3 minutes:

at forceless situation.......the Uref is close to 0........the voltage is still no change when apply force on it...

thx a lot

Added after 40 minutes:

sorry Karesz

after checking my connection.....
yr design is correct...........thx very much

1. U3,P2, R7
forceless: 146mV, 2.87k ohm

2. U4, R7
forceless: 185.3mV , 19.57k ohm

3. R5, R6, P3
forceless: 240mV, 26.4k ohm

is that right ???

thx a lot

 

[desmond]

Hi Karesz
Is me again,........the circuit is great......n now, i m doing a program display on LCD by connecting 8051.....my problem is that........the V+ is no much change whatever my force is adding on the sensor ...........therefore i cant get the value as same as the voltmeter

plx help