how to mesure the negative voltage with ADC0804?

[panther2005]

hi,
I have ADC0804 and i want to mesure the voltage from -5v to +5v but this circuit can't accept the negative voltage

 

[eramit123456]

use clapper circuit... it will increase ur dc level so -5 will be 0 and +5 will be +10...

 

[panther2005]

thanks for your answer,
with an OA in adder or resistors
a circuit please

but there is a problem of resolution
8 bits to 0-10v

 

[ark5230]

If the allowable voltage is +5V for the ADC then you may use a voltage divider to bring down the 0 - 10 V to a suitable level like 0 - 5 or 0 - 4.5V as per requirements. If 8 bit resolution is insufficient then you may go for a 10 bit or 12 bit ADC.

 

[panther2005]

here is my circuit to add 5v


it is functional to remove the negative voltage?

 

[ark5230]

I am not sure if the signal gets added as it will depend on source characteristics too.
Better approach could be to use both inverting and non inverting inputs for the offset.

See it this link helps
https://www.edaboard.com/threads/140800/

 

[panther2005]

my source is an electrode of potentiostat

 

[ark5230]

potentiostat with what output impedance, connecting external voltage is going to affect its performance ?

See if this link is useful

https://www.edaboard.com/threads/140800/

 

[panther2005]

300~500k
I think i need an impedance adapter with follower

 

[ark5230]

Again, I am not very sure but I feel the input is coming via R5 = 10K and connects to the output of U8 TL 431 which seems odd and the signal would die down as such sources have low output impedance.

 

[panther2005]

yes,
this is the circuit with simulation


input=-2v
offset (R6 10k)=2.5v

 

[ark5230]

Yes, now I got it. It should obviously work now provided the negative input does not go below -2.5 as you ADC can not handle -ve. U10 B output is 0.5 V, the ADC is 8 bit, will it make sense to increase the signal to a level suitable with the ADC. But you are done, once you are able to detect the signal, further refinement is no big deal.
Best luck
Raoof

 

[panther2005]

the best link for this problem:


MasteringElectronicsDesign.com : Design a Bipolar to Unipolar Converter to Drive an ADC

thanks Raoof

thanks for your replies

---------- Post added at 15:16 ---------- Previous post was at 15:04 ----------

the link for the impedance adaptator with electrode potentiostat:

**broken link removed**

 

[Tahmid]

Why don't you just use a differential amplifier with a gain of 1? And have a circuit that can detect if the input is positive and negative. That should be pretty simple.

Hope this helps.
Tahmid.

 

[panther2005]

Why don't you just use a differential amplifier with a gain of 1? And have a circuit that can detect if the input is positive and negative. That should be pretty simple.

Hope this helps.
Tahmid.

good idea , i will try it,

other solution:
i think the comparator is better, negative voltage---->low level, positive voltage---->high level (5v ttl)
but i must have a reserved pint in parallel port (all busy, 3 bits for mux4051 +8 bits for converted data+wr+int+++) and circuit to obtain the absolute value but the range is always 0-->5v