[SOLVED] Can anyone suggest me a low cost microcontroller with 8 bit ADC and 1 OP AMP

[Yogeshwari]

I want a low cost micro controller which has only 8-bit ADC and 1 op amp. Can anyone help me to select the same?

 

[KlausST]

Hi,

what is "low cost"?
* no pwer supply requirement?
* no IO nor interface requirement?
* no pin count requirement?
* no speed requirement?
* no memory (SRAM, EEPROM, Flash) requirement?
* no microcontroller family requirement?

... very unusal...

* even unusual is the requirement for a microcontroller_inside_OPAMP. Without OPAMP specifications. What do you want to do with the OPAMP?
(there are microcontrollers with comparators inside, but I can´t remember an Opamp..)

Most of the cheap microcontrollers I know have 10 bit ADCs. This should be no problem.

*****
If you have more requirements than those of your first post, then please post them all at once.

Klaus

 

[Yogeshwari]

Hi,

what is "low cost"?
* no pwer supply requirement?
* no IO nor interface requirement?
* no pin count requirement?
* no speed requirement?
* no memory (SRAM, EEPROM, Flash) requirement?
* no microcontroller family requirement?

... very unusal...

* even unusual is the requirement for a microcontroller_inside_OPAMP. Without OPAMP specifications. What do you want to do with the OPAMP?
(there are microcontrollers with comparators inside, but I can´t remember an Opamp..)

Most of the cheap microcontrollers I know have 10 bit ADCs. This should be no problem.

*****
If you have more requirements than those of your first post, then please post them all at once.

Klaus

Thanks for the reply.
I have to develop a circuit to process the signal from pressure sensor and display the pressure value in 7 segment display.
Output of the sensor is 1mV to 3mV. I want to amplify this signal, convert into digital signal and display it. So i need a micro controller to perform "Amplification and ADC" task.

 

[ud23]

You can go for cypress ,msp430,renesas,microchip this have low cost controller. things matter is which controller programming you know.

 

[KlausST]

Hi,

Output of the sensor is 1mV to 3mV

often Opamps have higher offset voltage than your signal.. and the offset drift surely matters.
I assume you need high gain, then you additionally should look for low noise Opamps.
I assume pressure sensor signal frequency is very low....

Now I have even more doubt you will find a suitable Opamp within a microcontroller.

I recommend to look for an external Opamp. It may be a tiny SOT-23 (-5 or -6) package, but you are flexible to select one with a suitable performance.
****
Your 7 segment needs to be driven. By what interace?
If you don´t have a special driver IC, then you need to drive the whole display by the microcontroller. LCD or LED? How many digits? Multiplexed? How many IO lines, what current....

Klaus

 

[Yogeshwari]

I am planning to use LMR321 OP AMP. If I can get a micro controller which has inbuilt OP AMP would be better.
Excluding OP AMP, which controller is better which has ADC. I don need high accuracy and all. Can you please suggest some low cost controller for the application?
I am planning to use BCD to 7 segment display driver to drive the & segment LED display. I want to display 3 digits from 0 to 100.

 

[KlausST]

Hi,

still a lot of informations missing.

LMR321: .. max. +/-5mV input offset voltage ... and your input signal is 1....3mV --> so your signal is smaller than the "unknown offset". Good luck.
Yes, you can calibrate the offset. But it will still drift with time, with temperature and with supply voltage...
The drift is unknown somehow. So you need to calibrate the offset every time before you start a measurement. Or you hope the offset doesn´t change.

Klaus

 

[Yogeshwari]

Hi,

still a lot of informations missing.

LMR321: .. max. +/-5mV input offset voltage ... and your input signal is 1....3mV --> so your signal is smaller than the "unknown offset". Good luck.
Yes, you can calibrate the offset. But it will still drift with time, with temperature and with supply voltage...
The drift is unknown somehow. So you need to calibrate the offset every time before you start a measurement. Or you hope the offset doesn´t change.

Klaus

Any suggestion for OP AMP which has low offset voltage?

 

[KlausST]

Hi,

If I look for an Opamp I use the website of a distributor. (For high volume I use the websites of manufacturers)
Like farnell, digikey, RS, mouser....
They usually have interactive selection guides

You may select your parts on electrical specifications, case, as well as availability and price...

Klaus

 

[udhay_cit]

1. I can suggest you to use an OPAMP with very low input offset voltage (also known as Chopper or auto zero or zero drift. the name varies with manufacturer but the functions are same). Non of the OPAMP which is embedded into the microcontroller will suitable to interface your sensor (except Cypress PSoC controller wich is very much expensive compared to the external OPAMP design). I will never suggest you to use the internal OPAMP of a microcontroller.

2. As you mentioned, 8 bit ADC is not enough for your requirement (in current days microcontrollers are comes with 10 bit at the least), but 10 bit or 12 bit Embedded microcontroller ADC is good enough with a good OPAMP design.

3. Cost: if your are looking for low cost microcontroller with high volume production, I can suggest you many (specially ST microcontroller) and it is worth to learn and write a program for the specific controller. If the requirement is low (below 100), it is better you to stick with whichever controller you are familier with. Example Microchip PIC16 series.

For very low cost OPAMP you can consider OP07 and LMV358 (see the specification) or you can use the link below for zero drift OPAMPs
https://www.digikey.com/product-sea...=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25


Udhay

 

[Yogeshwari]

1. I can suggest you to use an OPAMP with very low input offset voltage (also known as Chopper or auto zero or zero drift. the name varies with manufacturer but the functions are same). Non of the OPAMP which is embedded into the microcontroller will suitable to interface your sensor (except Cypress PSoC controller wich is very much expensive compared to the external OPAMP design). I will never suggest you to use the internal OPAMP of a microcontroller.

2. As you mentioned, 8 bit ADC is not enough for your requirement (in current days microcontrollers are comes with 10 bit at the least), but 10 bit or 12 bit Embedded microcontroller ADC is good enough with a good OPAMP design.

3. Cost: if your are looking for low cost microcontroller with high volume production, I can suggest you many (specially ST microcontroller) and it is worth to learn and write a program for the specific controller. If the requirement is low (below 100), it is better you to stick with whichever controller you are familier with. Example Microchip PIC16 series.

For very low cost OPAMP you can consider OP07 and LMV358 (see the specification) or you can use the link below for zero drift OPAMPs
https://www.digikey.com/product-sea...=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25


Udhay

Thank you so much Udhay for the valuable reply.
Input offset voltage of LM358 is 9mV. Can i use this op amp to amplify 1mV input signal?

 

[betwixt]

Input offset voltage of LM358 is 9mV. Can i use this op amp to amplify 1mV input signal?

Nothing is stopping you but it would be a bad choice. The output voltage could be as much as maximum input offset multiplied by the gain. For example, with a gain of x10 you might get as much as 90mV out WITH NO INPUT and it might increase to 100mV with 1mV of input you provide. In other words you 'dilute' the voltage you want to measure by mixing it with an unknown much larger voltage.

If you want your display to go to 100 with 3mV input, assuming you want to use an 8-bit ADC with 5V reference, the amplifier gain has to be approximately 1,700 to get full scale reading and the resolution (smallest change in voltage to make the display change) will be approximately 11uV. Consider that 11uV is hidden by ~780 times more error in the op-amp!

Almost all MCU have at least 10-Bit ADCs on board so why restrict yourself? What you are trying to do is quite feasible and not difficult but your plans to build it need some re-thinking.

Brian.

 

[udhay_cit]

Thank you so much Udhay for the valuable reply.
Input offset voltage of LM358 is 9mV. Can i use this op amp to amplify 1mV input signal?

I can't suggest you LM358 but you can use LMV358. Please compare the datasheet. The LMV358 has much better input offset voltage compare to the LM358 and the LMV series are with Rail-Rail output swing which is very much important.

You can think of OP07 also, which is very much better then LMV358, but its not a Rail-Rail OPAMP. You may need to give slightly higher supply voltage to get the required output from this OPAMP

Both OPAMPs are available all over the world (specially in INDIA) & these are very much inexpensive.


Udhay

 

[Yogeshwari]

I can't suggest you LM358 but you can use LMV358. Please compare the datasheet. The LMV358 has much better input offset voltage compare to the LM358 and the LMV series are with Rail-Rail output swing which is very much important.

You can think of OP07 also, which is very much better then LMV358, but its not a Rail-Rail OPAMP. You may need to give slightly higher supply voltage to get the required output from this OPAMP

Both OPAMPs are available all over the world (specially in INDIA) & these are very much inexpensive.


Udhay

Thank you so much Uday. I used LMV358 as differential amplifier and its working.