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ohm meter circuit with 8051

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desmond

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hi all....

I am doing a ohm meter.............does anyone has such a design circuit with 8051 and lcd display ???


thx a lot
 

pranam77

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desmond said:
hi all....I am doing a ohm meter...does anyone has such a design circuit with 8051 and lcd display ??? .....thx a lot
While dedicated chips like ICL7106 are available to make a LCD digital pannel meter, you'll just need some resistors to make a complete Ohm meter. For using 8051 you'll again need an ADC to convert the voltages from analogue to digital and write a code. Why take a long way?....Cheers
 

desmond

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thx a lot.......
i am doing a project with a force sensing resistor(sensor), 8051 and adc ........unfortunately the sensor is limited to current.........so i would like to built up a ohm meter in order to measure its value....

i have no idea with ICL7106, do u have any reference information... ???

thx a lot
 

karesz

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Hi,
You need a current source to that, in all caese, uninterested if is your ADC a 7106 Voltmeter Chip or some generell ADC...
K.
 

desmond

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hi karesz

my sensor is limited the current(sensor is from interlink force sensing resistor).........so......what can I do ???

so, alternately....i m going to built up a ohm meter to measure the ohm instead of measuring the voltage....
 

pranam77

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desmond said:
i have no idea with ICL7106, do u have any reference information... ??? thx a lot
You may refer the datasheet of the said component HERE
Cheers
 

karesz

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Hi desmond,
I dont know your sensor & interlink too, but if you send some datasheet/circuit?
I dont understand the problem if their signal is a voltage output_is it GND referenced or what is it pls?
If you have a force dependent current in sensors line: you can apply surly some smaller resistor in serie with them & in worst case sense hes voltage over an instr.-amp....
K.
 

desmond

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Hi karesz

I am using the circuit on page 23 fig 15. which is a current to voltage converter........but the voltage is saturated ........that is the problem i cant solve for a long time.....


thx a lot
 

karesz

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Hi desmond,
Tnx for datashet!
Is the output saturated with zero load, what are your Usupply, Uref & Rg values + desired force range pls?
K.

Added after 58 minutes:

If you have(force less) saturated output (I mean: practically at Vsupply); you must take smaller Uref or Rg, but the right way depends on your supplying too.
 

desmond

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Hi karesz

my Uref is 5V, Rg values is 4.7k..........i have tried different Rg values..............the results are the same which is saturated to 5V..........and now, i m going to measure the ohm instead of voltage

thx a lot
 

karesz

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Hali desmond,
you didnt answer thesituation: is 5V saturation the see if no force is applyed or only over some force applying_is your supply voltage than 5V?
If you have forceless 5V too?_your cricuit is wrong,to check it change the sensor first with some knowed, i.e. 2.2--3.3K, resistor... What is your OP Type pls?
I think you dont need a resistor cadaptor circuit to measure the sensed force.
Your sensor is relative unpreciuce/has much basis value band(+/-5--25%), for me; it need only simple electronic.
Maybe is your OP not a "rail-rail I/OP"t yp?
K.
 

desmond

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Hi karesz

sorry......

accodring to fig 15 from datasheet..........i use 4.7k ohm as RG, V+ connect to ground.........if at forceless situation, the voltage is 2.5V...........when i use a smaller value of resistor, the voltage decrease............and the voltage is saturated around 0.67V...........

my op-amp is lm358 which is recommended by the datasheet............

by the way......no matter i use different circuit provided by datasheet, the voltage wouldn't reach 5V no matter I applied force on it.....the voltage still saturated at some value ???


thx a lot
 

karesz

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Check pages 4 & 13 for In-Commonmode voltages pls...
If you supply it with only single voltage(+5V) you can have on the input max. ca. (+V)-1.5...-2V=~3.0...3.5V!
Datasheets fig. 15 refer in real case to +/- supply!
"With a positive reference voltage, the output of the op-amp must be able to swing below ground, from 0V to –VREF, therefore dual sided supplies are necessary."
Is your Ref-voltage negative pls?
K.
 

desmond

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Hi karesz

how can i connect with dual sided supplies with Ref-voltage negative.....i dun know at this point

thx a lot

Added after 24 minutes:

Hi karesz

thx for your help.....after consideration, i tihnk i may do a ohmmeter .....cos the max force of this circuit is 1lg, but in my applicaiton, the force is larger than this......so !!!

how can i show the resistor value by 8051 and adc0804 with simple circuit ???

thx a lot
 

karesz

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Hali,
Negative Uref means: your Gnd(or reference potential) of your Uref (is the +) on the cicuits GND to connect, you have than the "minus" to connect on the input...
What is your ref voltage source pls?
As simplest you can generate it from -supply per serial resistor & a Zener(or ref. voltage source IC), dont forget a bypass ~100nF...1uF:)...
K.

Added after 5 minutes:

If your force is larger as 1kg _sensor is OK up to ~10kg_ you need only a lower ref voltage as 5!, and corresponding dimensioning of Rg!!
Thes ccircuit is/can be OK up to 10 kg_but its (of course) your decision:)
K.
I believe, that thes is your simple circuit to connect some ADC_i.e. 0804 too...:)
 

desmond

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Hi karesz

i m very appricate your help.....but it is a bit difficult for me.....

can you give me some hint to make a ohmmeter by 8051 and adc0804...

thx a lot
 

karesz

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Your welcome, but i must make yet my job, on the evening; I will try it for you_ok?
K.
Pls tell me how is your Uref circuit maked?
 

desmond

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thx a lot .......

is that display the measured resistor value on lcd by 8051 and adc0804 ......

i think i give up to use current to voltage circuit ,,,,cos it only to use 1kg force that is not enough for my situation.....

thx a lot
 

desmond

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Hi karesz

can u teach me to display the resistor value on lcd by 8051 and adc0804...

thx a lot
 

karesz

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Hi,
Im sorry, but I didnt never write some programm, Im an "analog Type":)...
I assume, that you must storage in your uP some fix/standard comments as "Ohm" or "KOhm" or even direct the Forces :)...
If you send to display some newer value: you put it from two sources; 1, actual Force/voltage value & 2, after the character the Units from your "look up table", but how is it to coding_ sorry its not my profession...
K.
 

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