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ADC problem

Summary: 6 Replies, Latest post by Alqasir.M_2349726 on 20 May 2017 05:39 PM PDT
Verified Answers: 2
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Alqasir.M_2349726's picture
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6 posts

I am having a problem configuring my ADC in the way that is required. The range of my ADC is +/-6. We need to be configured that way; when the input voltage at -6V, then my ADC hex value should be 0x0000. When the voltage is 0V, then the LCD should display the half of my ADC value in hex, and my maximum ADC value which is 0xFFFF is equal to my maximum voltage which is +6V. 

Please check the attachment to observe my result. It's working, but the problem with it, the Voltage -0.001V is equal to 0xFFFF, but we need it to be the half of whatever the ADC value is, and my 0x0000 should be -6v. 

I am using the same kit as in the link below, which is PSoC 5LP.
http://www.cypress.com/documentation/development-kitsboards/cy8ckit-050-...

Thanks!

hli
user_78878863's picture
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2754 posts

You cannot handle negative voltages with the PSoC, they might even destroy it. (Except when using differential input, but even then the voltages cannot be below ground).

Apart from that: 0x000 corresponds to 0V, and negative voltages are represented as "two's complement" - a '-1' is then 0xFFFF. I think the ADC component data sheet explains that.

Alqasir.M_2349726's picture
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6 posts

I am using delsig ADC, and I am using the differential input mode. My range is +/-6.2. So, can you explain why I can't use a negative voltage? I thought this what the differential input mode for!

 

user_1377889's picture
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10711 posts

The PSoC (all of them) specify in absolute maximum ratings the lowest and highest voltage that may be applied to any pin. This is GND to Vdd,

No negative voltages (less than GND) are allowed.

 

Bob

Alqasir.M_2349726's picture
User
6 posts

That's so confusing to me. In the attached picture, I got the shot from the Delsig datasheet, it says the Delsig can take negative voltage. I am not talking about pins, I am talking about the ADC_Delsig.

Also, it allows me to setup the range at +/- voltage as it appears on the second shot. 

If the ADC_Delsig can't do negative, then what all these options in the second shot for?

 

Thanks!

hli
user_78878863's picture
User
2754 posts

Differential mode means that you have two input signals. Both are measured, at the same time, and the ADC returns the difference between them. This difference can be negative or positive, depending on which signal is larger. But the input signals itself cannot be negative voltages, with reference to ground. Doing so will destroy your PSoC.

Alqasir.M_2349726's picture
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6 posts

Okay, Thanks!

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