Tweet
as per the diagram, do you think it is feasible to use all four inputs with a single source device, so as to have the four outputs connected directly to atmega328p / arduino? In practice I would like to write a kind of 12-bit ADC (4x1024) doing the average calculation of the four outputs of the op-amp
-
-
Yes, that can be done but not best practice.
I would place a resistor(100 to 1k) in series with each op-amp input. This ensures the input bias current and input Voltage offsets from each op-amp are some what isolated.
LM324's are ok op-amps (jelly beans).
What is a bigger concern is not blowing up the Atmega's ADC input pins with an Over Voltage.
I have done that on PIC controller ADC inputs.
Is there any input protection on the Atmega's ADC pins???
What Voltages are you going to power the LM324?
Can they get to the Atmega's ADC pins? -
I don't use LM324 but I thought to use LF347 or similar with the resistances necessary to lower the voltage for the atmega328p ADC input and also 4 1n4148 on the op amp inputs.
explain to me the reason why it is not a good practice? at least I can evaluate whether it is worth doing this job or notComment
-
Ok. But diodes on op-amp input does nothing to ensure the op-amp OUTPUT does not fry the ATmega's ADC inputs.Originally posted by useus View Post
If the Atmega is run from +5 Volt and Gnd then you must ensure the Atmega input pins are NEVER taken higher than +5V ot lower than ground.
"I would place a resistor(100 to 1k) in series with each op-amp input. This ensures the input bias current and input Voltage offsets from each op-amp are some what isolated."explain to me the reason why it is not a good practice? at least I can evaluate whether it is worth doing this job or not
It is very doable and worth trying. Just a few details need to be taken care of.
If you do a PCB then having 'extra' parts like input series resistor makes tweaking the design easier and if you find they are not needed then easy to replace with a short (zero Ohm).
On the other hand, if no option for adding a part then you need to Cut Traces and solder parts to those traces.
You showed an LM324 so took this as what you planed to use.
The LF347 is a very different op-amp and is good for low noise pre-amp.
Looked at data sheet to see what the minimum Voltage it requires and they spec for +/-5V.
The LF347's output drive is not high (2k Ohm) which means it is not gtreat to drive an ADC input unless you run a longer ADC Sample time before conversion. It ok if the ADC sampling rate is slowish. Check the Atmega's data sheet for ADC input drive requirements.
? what is that coil you show in the diagram?Comment
-
Originally posted by waltr View Post
I explained myself wrong, I would use the diodes to stabilize the inputs and not allow for overhangs.
for the rest, thanks for the clarification, I will study well which op-amp to use!Comment
Comment