Discussion in 'Analog & Mixed-Signal Design' started by cRash1001, Mar 30, 2016.

1. ### cRash1001 Thread Starter New Member

Dec 22, 2015
15
0
I have two Analog Inputs of 5 VDC and 10-12 VDC. I need a 8 channel ADC that can accept this input voltage. Since 10 VDC exceeds the maximum input voltage of ADC Analog Input pin. I need a analog voltage Shifter that can convert my 5 VDC and 10-12VDC to required analog voltage and I want them to be configurable so I can configure any Analog Input for 5V or 10-12V. So what IC should I use?

*** I am still trying to understand what needs to be done so if you guys have any idea, plz suggest?

2. ### KeepItSimpleStupid Well-Known Member

Mar 4, 2014
1,260
222
Trying to understand what you wrote:

Is that 0-5V to 0-5V or virtually unchanged and
10-12 V to 0-5V?

or something else entirely. Sometimes 1-5 is better than 0 to 5 on a 5 V input.

3. ### cRash1001 Thread Starter New Member

Dec 22, 2015
15
0
I meant two analog inputs which have voltage values from 0-5V and 0-12V.

4. ### cmartinez AAC Fanatic!

Jan 17, 2007
3,698
2,756
What I'd do is use an ADC chip accepting 0 to 5V, and then condition the 0-12V signal by using a trimpot as a voltage divider, and then feed it to an op-amp configured as a voltage follower. This to make sure that the ADC chip receives a low impedance signal.

5. ### #12 Expert

Nov 30, 2010
16,665
7,313
I prefer fixed resistors.
The basic procedure is to use resistors to get your voltages down low enough for the ADC then amplify them afterwards.
You didn't say whether the ADC can work with 5 volts. If it can, something like 14k first, then 10k, and your 12 volts is down to 5 volts at the middle of the two resistors.
If you need better precision, that's why 1% resistors were invented...or the trimpot approach, but I would use 12k and a 5k trimpot, not a 25k trimpot. The less pot, the easier it is to hit the sweet spot.

Or, you could just use a 15k and a 10k, run 4.8 volts into your ADC and adjust for precision after the ADC.
There are several ways to adjust things just right, but they all start with a resistive voltage divider.

6. ### dannyf Well-Known Member

Sep 13, 2015
2,196
417
A resistive divider?

7. ### #12 Expert

Nov 30, 2010
16,665
7,313
Yeah, as in , "not inductive" and, "not capacitive".
Whatsamatta? You didn't learn your vocabulary in 1960?

8. ### cmartinez AAC Fanatic!

Jan 17, 2007
3,698
2,756
mmhhh... I don't know #12... I was under the impression that you meant something like "resistance is futile" until you clarified

#12 likes this.
9. ### cRash1001 Thread Starter New Member

Dec 22, 2015
15
0
What I am looking for an IC with 8 Analog Inputs Channels each of which are programmable for any one of the standard analog sensor input ranges(0 to 5V, 0 to 10V, ±5V, or ±10V, 0-20 mA, 4-20 mA). I want this to be of at least 16 bits or more. It would be better if all this comes with a ADC too. So guys any suggestions to where should I look into?

10. ### eetech00 Active Member

Jun 8, 2013
676
116
Microchip has them. They also have analog frontends..