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Questions regarding voltage divider for micro controller sensing?

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farukhkhanugi:
Hello Guys,

I am beginner trying to develop two voltage sensors for attiny85 microcontroller. I have two separate voltage levels that I want to sense using the attiny. One of the voltage supply is 0V-5.5V and is fluctuating very often within that range, and I want to detect the voltage every second or so through attiny85 analogread function and record it inside a log. I want to use the VS1 sense line from the schematic and connect it directly to any analog pin of the attiny85. And the SIN is directly connected to the supply voltage. On the other supply, I have linear 0V-2.7V which is connected directly to the CVP pin. And the VS2 is connected directly to another analog pin of the attiny85.

The attiny85 is being powered by a separate 3.3V supply. And the reference voltage I want to use is 1.35V inside the software. So, 0V-1.35V inside the attiny analogread to detect this 0V-5.5V fluctuating range and 0V-2.7V linear range.

Now, the questions:
1. Is my voltage divider circuits feasible and a good approach for these two types of voltage measurements?
2. Is it possible to improve the voltage sense circuitry, to get better accurate readings?
3. What high quality good brand SMD components I could use for these voltage sense circuits and their eagle library parts suggestions?


Any suggestions and tips would be highly appreciated. Thank You.

MosherIV:
Hi

I would not put the capacitors in, they would have to be charged/discharged by the voltage being measured. If you must have them, use nF not uF.

I do not think you need a voltage divider for a 1:1 No point.

You may want to think about input protection, after the voltage divider, on the lower resistor put a 3.3V zener to stop any accidental over volt to the micro input.

farukhkhanugi:
What if I use 3.3uF @ 50V caps? Or can you please suggest a capacitor type for this application. what nF and what voltage value caps I should use here. And should I use ceramic type non polar caps or electrolytic or cermamic polarized ones. I just want to keep the voltage reading consistent and detectable through the micro.

I did not understand what you meant by 1:1 no point.

the supply voltage I am using cannot possibly overshoot voltages more than 5.5V. Even though can you please show me an schematic example which will add the zener to the circuit? I am not sure how to implement a zener for this circuit. Wouldn't I need another resistor for the zener?

farukhkhanugi:
The supply voltage 1 in this case is couple of 5V rated solar panels in parallel and the supply voltage 2 is a supercapacitor bank. And the solarcaps are being charged through a buck from the solar. Is it really possible for these two supplies to generate voltage spikes?

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